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Theses and Dissertations

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Seismic Attribute Fracture Analysis and Thin and Thick-Skinned Seismic Attribute Fracture Analysis and Thin and Thick-Skinned

Structural Controls on the Evolution of a Foreland Basin - Structural Controls on the Evolution of a Foreland Basin -

Parrando and Guavio Anticlines, Eastern Cordillera Foothills, Parrando and Guavio Anticlines, Eastern Cordillera Foothills,

Colombia Colombia

Ibraheem Khalil Hafiz

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Recommended Citation Recommended Citation Hafiz, I. K.(2020). Seismic Attribute Fracture Analysis and Thin and Thick-Skinned Structural Controls on the Evolution of a Foreland Basin - Parrando and Guavio Anticlines, Eastern Cordillera Foothills, Colombia. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5962

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SEISMIC ATTRIBUTE FRACTURE ANALYSIS AND THIN AND THICK-SKINNED

STRUCTURAL CONTROLS ON THE EVOLUTION OF A FORELAND BASIN -

PARRANDO AND GUAVIO ANTICLINES, EASTERN CORDILLERA FOOTHILLS,

COLOMBIA

by

Ibraheem Khalil Hafiz

Bachelor of Science

King Abdulaziz University, 2006

Master of Science

King Saud University, 2012

Submitted in Partial Fulfillment of the Requirements

For the Degree of Doctor of Philosophy in

Geological Sciences

College of Arts and Sciences

University of South Carolina

2020

Accepted by:

James Kellogg, Major Professor

Scott White, Committee Member

Alicia Wilson, Committee Member

Obi Egbue, Committee Member

Cheryl L. Addy, Vice Provost and Dean of the Graduate School

ii

© Copyright by Ibraheem Khalil Hafiz, 2020

All Rights Reserved.

iii

DEDICATION

At the end of my Ph.D. journey, I would like to dedicate these achievements to my

parents, who encouraged me to continue my education and supported me all these years,

and to my wife, Rabab Albaba, who stood beside me and helped me in even the most

difficult times, caring for our family and always there when I need help.

iv

ACKNOWLEDGMENTS

First of all, I would like to give the most profound appreciation to my doctoral

advisor Dr. James Kellogg for his support, guidance, and mentorship throughout my Ph.D.

journey. I would like to thank my committee members, Dr. Obi Egbue, Dr. Scott White,

and Dr. Alicia Wilson, for insightful discussions and recommendations that improved the

quality of my thesis dissertation.

Thanks to Frontera Energy (formerly Pacific Energy) for generously making 2D

and 3D seismic and well data available for this research. Also thanks to the Colombian

Geological Survey for providing surface geology maps, and to Petroleum Experts for

providing Move structural software, and to Schlumberger for generously donating Petrel

2015 and PetroMod 2017 software.

I would like to thank my sponsor King Abdulaziz City for Science and Technology

(KACST) in Saudi Arabia, for my full scholarship for doctoral studies, as well as the

School of the Earth, Ocean, and Environment in the College of Arts and Sciences at the

University of South Carolina for its support.

v

ABSTRACT

The Parrando and Guavio anticlines are located in the Llanos foothills on the

eastern flank of the Eastern Cordillera of Colombia. This study presents new 3D horizon

maps, seismic and stratigraphic interpretations, and 1D burial models based on a 3D

seismic volume, 2D seismic lines, and well logs. The Guavio anticline was formed by

overlapping Miocene-Pliocene fault-bend folds and inversion of the Guaicaramo normal

fault. Unlike previous models, the basement fold is interpreted as formed by a ramp from

pre-Cretaceous basement to a double wedge fault probably preceded by a thin-skinned

bedding plane thrust fault. A new 1D burial model predicts that source rocks began to expel

oil at 18 Ma, 10 Myr before trap formation. The Parrando anticline is a thin-skinned fault-

bend fold southeast of the Guavio anticline with a forelimb break through fault.

Previous studies of fractures in the Foothills relied on surface geologic studies or

downhole imager logs. In this study, attribute analysis and ant-tracking algorithms on a 3D

seismic volume were used to produce curvature and fracture network maps for the Parrando

anticline. Two prominent fracture systems were observed, NE-SW and NW-SE. The major

fracture strike azimuth is NE-SW, parallel to the structural trend of the Foothills,

concentrated in folded rocks of the Parrando anticline. Several NE-SW fractures show

extensional displacement consistent with folding or an elastic plate subjected to pure

bending. NE-SW fractures in the Late Cretaceous source rocks may have been inherited

from Early Cretaceous rifting, while those in the Oligocene Carbonera Fm may have been

vi

early folding or bending of the lithosphere before the advancing mountain front. The

secondary fracture strike azimuth is NW-SE perpendicular to the structural trend of the

Foothills. NW-SE fractures are found in strata from 21 to 6 Ma and are most intense in

mid-Miocene (14 Ma). These may be inherited from earlier initial folding and thrusting

on the Guaicaramo fault. This method permits the mapping of fracture systems in rock

volumes between wells, and in areas where no well borehole imagery logs are available.

vii

TABLE OF CONTENTS

DEDICATION ................................................................................................................... iii

ACKNOWLEDGEMENTS ............................................................................................... iv

ABSTRACT .........................................................................................................................v

LIST OF FIGURES ........................................................................................................... ix

CHAPTER I TECTONIC SETTING OF THE NORTH ANDES, COLOMBIA,

SOUTH AMERICA ......................................................................................................1

1.1 INTRODUCTION ...................................................................................................1

1.2 TECTONIC EVOLUTION OF NORTH ANDES ..................................................2

1.3 DATA SET AND METHODOLOGY .....................................................................8

CHAPTER II THIN-SKINNED AND THICK-SKINNED STRUCTURAL

CONTROL ON THE EVOLUTION OF A FORELAND BASIN

PETROLEUM SYSTEM-PARRANDO AND GUAVIO ANTICLINES,

EASTERN CORDILLERA LLANOS FOOTHILLS, COLOMBIA ............................9

2.1 OVERVIEW ............................................................................................................9

2.2 INTRODUCTION .................................................................................................10

2.3 GEOLOGIC SETTING .........................................................................................13

2.4 DATA AND METHODOLOGY ...........................................................................20

2.5 RESULTS ..............................................................................................................22

2.6 DISCUSSION ........................................................................................................39

2.7 CONCLUSIONS....................................................................................................44

CHAPTER III 3D SEISMIC ATTRIBUTES ANALYSIS OF SUBSURFACE

FAULT AND FRACTURE SYSTEMS FOR PARRANDO ANTICLINE

LLANOS FOOTHILLS COLOMBIA .........................................................................46

viii

3.1 OVERVIEW ..........................................................................................................46

3.2 INTRODUCTION .................................................................................................47

3.3 GEOLOGIC SETTING .........................................................................................49

3.4 DATA AND WORKFLOW ..................................................................................59

3.5 PARRANDO AND CHAPARRAL FAULT SYSTEMS ......................................67

3.6 DISCUSSION ........................................................................................................79

3.7 CONCLUSION ......................................................................................................80

CHAPTER IV POTENTIAL APPLICATIONS FOR 3D SEISMIC

ATTRIBUTE FRACTURE ANALYSIS .....................................................................82

4.1 EVOLUTION OF REGIONAL STRESS FIELDS ..............................................83

4.2 RESERVOIR STIMULATION, GEOTHERMAL, CO2 SEQUESTRATION,

PASSIVE SEISMIC ..............................................................................................84

4.3 HYDROLOGY ......................................................................................................86

4.4 MINERAL EXPLORATION ...............................................................................87

4.5 FUTURE WORK ...................................................................................................89

REFERENCES ..................................................................................................................91

APPENDIX A: PERMISSION TO REPRINT ...............................................................104

ix

LIST OF FIGURES

Figure 1.1 Tectonic map of the north Andes. ......................................................................7

Figure 2.1 A. Tectonic map of the north Andes. B. Eastern Cordillera regional map.

C. Geologic location map of the study area. .................................................................12

Figure 2.2 Stratigraphic column for Llanos foothills. ........................................................19

Figure 2.3 Velocity model and well tie for Medina-1. ......................................................26

Figure 2.4 Time-depth relationship and well tie for Parrando-1. ......................................27

Figure 2.5 Uninterpreted and interpreted seismic profiles of the Guavio anticline and

Guaicaramo thrust. ......................................................................................................29

Figure 2.6 Uninterpreted and interpreted seismic profile parallel to structural strike of

the Guavio anticline. ...................................................................................................30

Figure 2.7 Extended profile for Fig. 2.5 to the northwest showing the Tesalia fault and

Nazareth syncline. ........................................................................................................32

Figure 2.8 Retro-deformed cross section for Guavio anticline. .........................................37

Figure 2.9 Uninterpreted and interpreted seismic profiles of Parrando anticline. .............38

Figure 2.10 Burial histories for source rocks (Gacheta/Chipaque Formation). .................40

Figure 2.11 Petroleum system evolution for Medina basin and adjacent Parrando

anticline ........................................................................................................................41

Figure 3.1 Location map of the study area. .......................................................................49

Figure 3.2 Stratigraphic column for Llanos foothills Fm. .................................................53

Figure 3.3 Uninterpreted and interpreted seismic profiles of the Cusiana structure. ........56

x

Figure 3.4 Uninterpreted and interpreted seismic profile of Rio-Chitamena structure. ....57

Figure 3.5 Uninterpreted and interpreted seismic profiles of Parrando anticline ..............58

Figure 3.6 3D seismic data, a) Show raw data before filtering and cropping. b) show the

unwanted cropping data ..................................................................................................60

Figure 3.7 Fracture analysis workflow. .............................................................................61

Figure 3.8 Pre-condition process. a) the raw data Inline 147 before applied any filter.

b) Inline 147, after using the structural smoothing attribute. ...............................................64

Figure 3.9 Pre-condition process for time slice -2549ms. a) Chaos, and b) Variance attributes. .64

Figure 3.10 Ant tracking result in time slice -2891ms. ...........................................................66

Figure 3.11 Fault and fracture extraction from the ant tracks volume. .....................................66

Figure 3.12 Fault modeling for Parrando anticline. ...........................................................68

Figure 3.13 Parrando thrust fault. ......................................................................................70

Figure 3.14. Ant tracking fracture rose diagrams and histogram dipping over 75 degrees. ...76

Figure 3.15. Horizon ant-tracking fracture networks .........................................................77

Figure 3.16. Ant-tracking time slices and seismic profiles ................................................78

1

CHAPTER I

TECTONIC SETTING OF THE NORTH ANDES, COLOMBIA, SOUTH

AMERICA

1.1. INTRODUCTION

The Medina Basin and Llanos foothills are located in the eastern foreland of the

Eastern Cordillera of Colombia and are separated by the Guaicaramo fault (Fig. 2.1).

Northwest of the Guaicaramo fault is the Guavio anticline, a large anticline with 4-way

closure and seal but no commercial hydrocarbons. Southeast of the Guaicaramo fault is the

Parrando anticline, located south of the giant Cusiana oil field (more than 1.25 billion

barrels of oil). The chapters of this dissertation are cover the structural evolution of the

petroleum systems and the subsurface fracture systems of the foreland basins. Chapter 2

presentsnew 3D horizon maps, seismic and stratigraphic interpretations, and 1D basin

models. Interpretations of the Guavio and Parrando anticlines are based on 2D and 3D

seismic reflection profiles assuming conservation of volume (Suppe, 1983). The Guavio

anticline was retrodeformed to test my interpretation and to relate the timing of

hydrocarbon expulsion (Medina-1 1D model) to the timing of Guavio trap formation. The

results offer a possible explanation for the lack of commercial hydrocarbons in the Medina-

1 well. The new interpretations in this chapter show that the Guacaramo thrust fault

involved “thin-skinned” and “thick-skinned” deformation, fault-bend folding, and for the

first time wedge faulting. This study also presented the first structural interpretation of the

2

Parrando anticline, a gentle fault-bend fold and breakthrough fault. Finally, I created

schematic maps to illustrate the evolution of the eastern foothills petroleum system. In

chapter 3, I used attribute analysis and ant-tracking algorithms on a 3D seismic volume

(246 km² 5000 msec) to produce a new 3D fault model, seismic attribute analysis,

curvature, and fracture network maps for the Parrando anticline. This method allows

mapping of fracture-set orientations throughout an entire sedimentary section, as well as

the differential stresses that were active during their propagation through time (Engelder

and Geiser, 1980). By comparing fractures in folded rock units to those in non-folded rocks,

fold models for fracture initiation can be evaluated (e.g., Stearns, 1968).

1.2. TECTONIC EVOLUTION OF NORTH ANDES

The Cenozoic evolution of the northern Andes involved slip partitioning at an

obliquely convergent plate boundary, mountain building rates and styles correlated with

convergent boundary processes, and active arc-continent collision and accretion. Buoyant

Caribbean crust has been amagmatically subducting under the North Andes for 75 Myr

(Kellogg et al., 2019). Convergent boundary forces have inverted and shortened a basin up

to 150 km forming the Eastern Cordillera mountain range. Six “US Rocky Mountain

Laramide-style” (basement block) mountain ranges have been rapidly uplifted 7–12 km in

the last 10 Myr, and several island arcs have collided with the North Andean margin. GPS

results show that the Panama arc is actively colliding with the North Andean Block (NAB),

having recently formed a land bridge between the Americas, separating the Atlantic and

Pacific Oceans (e.g., Freymueller et al., 1993; Mora-Páez et al., 2019). Part of the Panama-

Choco arc has recently accreted to the North Andean Block (Kellogg and Mora-Páez,

3

2016), and the entire block has begun to slide parallel to the continental margin toward the

Caribbean (e.g., Ego et al., 1996; Audemard et al., 1999; Tibaldi et al., 2007; Egbue and

Kellogg, 2010).

The buoyant Caribbean lithosphere is subducting under the northern Andes at a low

angle. Flat slab subduction is often characterized by a lack of a volcanic arc because there

is no asthenospheric wedge in the overriding plate, with resultant low heat flow, and rigid

thick-skinned “Laramide” style basement tectonics (e.g., Smithson et al., 1978; DeCelles,

2004; Fan and Carrapa, 2014). The basement block, “germanotype,” or “thick-skinned”

tectonic style of the Laramide orogeny in the central and southern Rocky Mountains of the

United States was characterized by broad zones of uniform strike and dip separated by

narrow zones of steeper dips or high-angle faults. Examples of “thick-skinned” basement

tectonics are found throughout the Laramide US Rocky Mountains (e.g., Smithson et al.,

1978; Miller and Mitra, 2011) and the Sierras Pampeanas in Argentina (Jordan and

Allmendinger, 1986; Ramos et al., 2002; Fan and Carrapa, 2014), as well as in the northern

Andes (e.g., Kellogg and Bonini, 1982; De Toni and Kellogg, 1993). Prior to the basement

Laramide orogeny in the US Rocky Mountains, the region was the site of a Cordilleran

foreland basin associated with thin-skinned deformation and flexural loading of a fold and-

thrust belt. Subsequent thick-skinned deformation (Laramide orogeny) partitioned the

regional foreland basin and caused >4 km of localized exhumation of crystalline basement

blocks, accompanied by localized subsidence of intermontane basins. It is generally

accepted that the switch of deformation style from thin skinned to thick skinned was caused

by the change from normal high-angle subduction to low-angle subduction of buoyant

4

Farallon oceanic lithosphere beneath western North America (e.g., Liu et al., 2008; Fan

and Carrapa, 2014).

The Cenozoic orogenic evolution of the northern Andes included numerous Laramide-

style basement uplifts, correlating with Caribbean flat slab subduction. Across the northern

Andes, basement blocks were rapidly uplifted 7–12 km in the last 10 m.y., including the

Venezuelan Andes (De Toni and Kellogg, 1993), Sierra de Perija (Shagam, 1980; Kellogg

and Bonini, 1982), Santander Massif (Amaya et al., 2017), Eastern Cordillera; Gregory-

Wodzicki, 2000; Mora et al., 2010b; Anderson et al., 2016), Garzon Massif (Saeid et al.,

2017), and the Santa Marta Massif (Villagómez et al., 2011) (For location of uplifts see

Fig. 1). The spatial distribution of these numerous Laramide-style basement block uplifts

correlates with buoyant Caribbean low-angle to flat slab subduction and resultant low heat

flow. The timing (last 10 Myr), spatial distribution and orientation, and high rates of

shortening (5–15 mm/yr) and uplift (0.5–1.0 mm/yr) also suggest that the uplifts were

accelerated by the Panama-Choco—North Andes arc-continent collision and accretion,

especially the Eastern Cordillera of Colombia (e.g., Kellogg and Vega, 1995; Egbue et al.,

2014).

About 12–15 Ma the Eastern Cordillera of Colombia became a major sediment source

(Gregory-Wodzicki, 2000; Mora et al., 2014), although some sediments were being

supplied to the Eastern Foothills area as early as the Oligocene (Mora et al., 2010a; Saylor

et al., 2012). Paleobotanical data (Fig. 6a; Wijninga, 1996; Gregory-Wodzicki, 2000) and

apatite fission-track ages (Mora et al., 2008; Mora et al., 2010b) indicate that most of the

uplift in the central and eastern flank of the Eastern Cordillera occurred in the last 12 Ma.

5

Paleo-precipitation data from the Upper Magdalena Valley indicate that a substantial

orographic barrier was not fully established until 6–3 Ma, when>1 km/m.y. of material was

exhumed (Anderson et al., 2016). Based on minimum exhumational ages provided by new

apatite FTA data, as well as thermal history modeling, Anderson et al. (2016) suggest that

thrust induced rapid exhumation of the southern Eastern Cordillera was focused between

6.4 Ma and 3 Ma.

By the early Pleistocene, in addition to the compressional stress regime, a NE-SW

strike-slip component was introduced as the northern Andes began to “escape”. Egbue and

Kellogg (2010) compiled field geologic estimates of northeastward displacement rates for

the North Andes with a mean estimated geologic slip rate for the last 86,000 years of 7.6

mm/yr. The earliest measurements date back to the opening of the Gulf of Guayaquil at 1.8

Ma, and the northeastward displacement of the North Andes has been interpreted as

tectonic escape from the Carnegie Ridge subducting at the Ecuador trench (Egbue and

Kellogg, 2010; Nocquet et al., 2014; Chlieh et al., 2014). Presently, in the Eastern

Cordillera the escape rate (8.1 mm/yr) is greater than the rate of range normal shortening

(4.3 mm/yr) (Mora-Paez et al., 2019).

During the Mesozoic era, the area of the modern Eastern Cordillera was an extensional

basin. Northwestern South America was affected by rifting related to the break up of

Pangea and the eventual separation of North and South America (Pindell and Dewey, 1982;

Ross and Scotese, 1988; Cediel et al., 2003). Late Cretaceous post-rift thermal subsidence

provided accommodation space for the deposition of hydrocarbon source and reservoir

rocks. Eocene eastward subduction of the Caribbean beneath the North Andes led to uplift

6

in the Central Cordillera and the development of a foredeep and more reservoir rocks. The

Miocene to Present Panama arc-North Andes collision inverted Mesozoic basins, and

produced rapid uplift of the Eastern Cordillera and hydrocarbon structural traps in the

Llanos Foothills. The collision related stress field also resulted in fracture sets parallel to

the maximum compressive stress direction and fold-related fractures normal to the

maximum stress, providing possible migration pathways and increased fracture porosity

and permeability.

7

Figure. 1.1. Tectonic map of the North Andes (Kellogg et al., 2019). Abbreviations: CB,

Choco block; CC, Central Cordillera; COR, Cocos Ridge; CR, Carnegie Ridge; EAFS, East

Andean fault system; EC, Eastern Cordillera; G, Gorgona Island; GM, Garzon massif; MA,

Merida (Venezuelan) Andes; NAB, North Andean block; P: Sierra de Perija; PB, Panama

block; SCDB, South Caribbean deformed belt; SM, Santander Massif; SN, Sierra Nevada

de Santa Marta; WC, Western Cordillera.

8

1.3. DATA SET AND METHODOLOGY

Data for this dissertation has been provided by Frontera Energy. Geophysical data

(Fig. 2.1) include 3D seismic volume-(Block: LLA 31): Number of inlines = 631, Number

of crosslines = 630, Inline length = 18.9 km, Inline interval = 30 m, Crossline length = 18.9

km, Crossline interval = 30 m, Sample interval = 2 ms, Record length = 5000 ms. In

addition, 194 2D seismic lines: 77 2D seismic lines inside Block LLA 31, total length =

176 km, sample interval = 2 ms, record length = 5000 ms. Well logs:18 drilled wells: 6

wells inside the Block LLA 31, plus 12 wells around the block, provided with caliper,

gamma-ray, sonic, density and checkshot surveys. In addition, the Colombian National

Hydrocarbon Agency (ANH) provided surface geology maps including plate 229 with a

scale of 1:100000 with booklet (2013).

This dissertation research integrates geophysical and geological interpretations to

present the tectonostratigraphic evolution and petroleum system of the Eastern Cordillera

Foothills and adjacent basins. The methodology includes seismic interpretation, seismic

attribute analyses, structural modeling, stratigraphic interpretation, 1D basin modeling, and

petroleum system analyses. The seismic interpretation workflow uses Petrel 2015 to pick

horizons with well control, regional seismic stratigraphy, structural maps in time, and

seismic attribute fracture analysis.). Move software with seismic, well, and surface geology

control was used to create volume-balanced retrodeformed geologic cross sections.

Petroleum systems analysis utilized PetroMod 2013.1 to generate 1D basin models

including burial history curves and source rock maturity.

9

CHAPTER II

THIN-SKINNED AND THICK-SKINNED STRUCTURAL CONTROL

ON THE EVOLUTION OF A FORELAND BASIN PETROLEUM

SYSTEM - PARRANDO AND GUAVIO ANTICLINES, EASTERN

CORDILLERA LLANOS FOOTHILLS, COLOMBIA (1)

2.1 OVERVIEW

The Parrando anticline is located in the Llanos foothills on the eastern flank of the

Eastern Cordillera of Colombia. To the northwest of the Parrando anticline area is the

Guavio anticline, a large fault-bend fold, a structure that appears to be an unbreached trap

with four-way closure and seal, but test wells show no commercial amounts of petroleum.

Just 65km to the northeast along strike is the giant Cusiana oil field. This study presents

new 3D horizon maps, seismic and stratigraphic interpretations, and 1D basin models based

on a 3D seismic volume (246km2 5000 msec), 70 2D seismic lines (176km), 18 wells with

well log data and final well reports. A small fault-bend fold in the footwall of the Parrando

thrust appears to have 4-way closure for a Mirador Formation trap. 1D models suggest

hydrocarbon generation from 8 to 5Ma, similar to the Cusiana system, but high-angle

normal and transpressive faults may have permitted hydrocarbon escape. Just to the

(1) Hafiz, I., J. Kellogg, E. Saeid, Z. Albesher, 2019, Journal of South American Earth

Sciences, Volume 96, December 2019, Doi.org/10.1016/j.jsames.2019.102373

Reprinted here with permission of publisher. Appendix A

10

northwest across the Guaicaramo fault, the Guavio structure was formed by overlapping

fault-bend folds (total relief 3.5km) during late Miocene-Pliocene age (6-3Ma) shortening

(minimum 20km) and inversion of the Guaicaramo normal fault. Unlike previous models

we interpret the basement fold as formed by a ramp from pre Cretaceous basement to a

double wedge fault, folding the Guaicaramo thrust footwall rocks. A thin-skinned bedding

plane thrust fault ramping to the surface along the Guaicaramo fault may have preceded

the formation of the Guavio anticline. Our 1D basin model for the Medina-1 well predicts

that the Gacheta Formation source rocks began to expel oil at 18Ma, at least 10 Myr before

trap formation. The timing of thick-skinned and thin-skinned deformation, and trap

formation were critical factors in the evolution of the Guavio, Parrando, and Cusiana

petroleum systems. Most of the Guavio deformation results from repeated inversion of the

Mesozoic Guaicaramo basin-bounding normal fault.

KEY WORDS: Guavio structure, Guavio anticline, Parrando anticline, Eastern

Cordillera, Petroleum system, Guaicaramo fault

2.2 INTRODUCTION

The Guavio anticline (Fig. 2.1) is a large fault-bend fold located 11 km northwest of

the Guaicaramo fault, a structure that appears to be an unbreached trap with four-way

closure and seal, but test wells show no commercial amounts of petroleum. But only 65 km

east across the Guaicaramo fault is the giant Cusiana oil field. Is the different petroleum

potential related to timing and structural control on the evolution of the petroleum systems?

The petroleum system at Cusiana has been well described (e.g., Cooper et al., 1995; Cazier

et al., 1995), but the lack of economic hydrocarbons at Guavio has not been explained. In

11

this paper we examine the timing and structural evolution of the Guavio anticline northwest

of the Guaicaramo fault and the Parrando anticline southeast of the fault.

The Eastern Cordillera was formed by the inversion and shortening of Jurassic-Early

Cretaceous back arc basins. The timing of the initial uplift of the Eastern Cordillera remains

poorly constrained, with estimates ranging from 60 to 25 Ma (e.g., Horton et al., 2010a;

Mora et al., 2010a). Maximum tectonic inversion and shortening in the Eastern Cordillera

occurred in the middle Miocene to Pliocene (Van der Hammen, 1958; Dengo and Covey,

1993; Cooper et al., 1995) and has been attributed to the collision of the Baudó-Panama

arc with the western active margin of South America (Duque-Caro, 1990; Kellogg et al.,

2019). Estimates of shortening range from 70km (Cooper et al., 1995; Tesón et al., 2013;

Mora et al., 2013) to 150km or more (Dengo and Covey, 1993; Roeder and Chamberlain,

1995). Conflicting views remain as to the nature of thrusting, whether dominantly thin- or

thickskinned, and to the magnitude of the associated thrust displacements.

Dengo and Covey (1993) proposed that the Eastern Cordillera is essentially an east-

verging structure formed during two main tectonic phases. The first tectonic phase induced

a thin-skinned basement detached style that created large, east-verging thrust faults with

the greatest shortening in the middle Miocene to Pliocene (Cortés et al., 2006). During the

Pliocene, deformation changed to basement involved as Jurassic and Early Cretaceous

normal faults were inverted (Dengo and Covey, 1993). Other reconstructions of the Eastern

Cordillera attribute most of the deformation to inversion of mid-crustal normal faults or

thick-skinned deformation with minimal thin-skinned thrusting (e.g., Cooper et al., 1995;

Mora et al., 2015). This study was based on a rich dataset provided by Frontera Energy

Colombia, including a 3D seismic volume (246km2, inlines: 631, crosslines: 630), 77 2D

12

seismic lines (176km), 18 wells with caliper, gamma-ray, sonic, density logs, check-shot

surveys, and reports. We produced new 3D horizon maps, seismic and stratigraphic

interpretations, and 1D basin models.

Figure 2.1. A. Tectonic map of the north Andes, showing block and plate boundaries after

Cediel et al. (2003), Taboada et al. (2000), Symithe et al. (2015), and Kellogg et al. (2019).

Abbreviations: CB, Choco block; CC, Central Cordillera; COR, EC, Eastern Cordillera;

GM, Garzón Massif; MA, Merida (Venezuelan) Andes; NAB, North Andean block; P:

Sierra de Perija; PB, Panama block; SM, Santander Massif; SN, Sierra Nevada de Santa

Marta; WC, Western Cordillera. B.Eastern Cordillera regional map. C. Geologic location

map of the study area- Parrando anticline and Guavio anticline after Alcárcel et al. (2017).

Blue dots: apatite fission track age sample locations (Mora et al., 2010b). (For

interpretation of the references to color in this figure legend, the reader is referred to the

Web version of this article.).

13

We interpreted the Guavio and Parrando anticlines from 2D and 3D seismic reflection

profiles using volume balancing methods (Suppe, 1983). We then retrodeformed the

Guavio anticline to relate the timing of hydrocarbon expulsion (Medina-1 1D model) to

the timing of Guavio trap formation, offering a possible explanation for the lack of

commercial hydrocarbons in the Medina-1 well. We show that the Guacaramo thrust fault

involved “thin-skinned” and “thick-skinned” deformation, fault-bend folding, and for the

first time wedge faulting. We present the first structural interpretation of the Parrando

anticline, a gentle fault-bend fold and breakthrough fault. Finally, we create schematic

maps to illustrate the evolution of the eastern foothills petroleum system.

2.3 GEOLOGIC SETTING

2.3.1 REGIONAL TECTONICS

Precambrian-early Paleozoic metamorphic rocks underlie the Central and Eastern

Cordilleras (Cooper et al., 1995). During the Jurassic and Early Cretaceous, two rift basins

developed in the Eastern Cordillera, either related to the separation of North America and

South America (Jaillard et al., 1990) or extension in a backarc setting (Maze, 1984).

Tectonic subsidence from extension and crustal thinning was followed by Cretaceous

thermal subsidence as the lithosphere thermally equilibrated (Ojeda and Thesis, 1996). The

thickness of Cretaceous basin fill is estimated to be from 5km (Restrepo-Pace, 1989) to

8km (Cardozo Puentes, 1988). At ~75Ma, the Caribbean Large Igneous Province (CLIP)

collided with South America, resulting in the accretion of the oceanic terrane of the

Western Cordillera (Spikings et al., 2015). Subsequently buoyant Caribbean crust began a

magmatically subducting under the North Andes, resulting in flat slab subduction and

basement block uplifts in the overriding plate (Kellogg et al., 2019). 50 million years ago,

14

the Caribbean plate ran into the Bahamas Bank on the North American plate and its motion

relative to the American plates changed dramatically (Boschman et al., 2014). In the past

50 million years the Caribbean has moved 1000km eastward relative to the North and South

American plates. The resulting up lift of the Central Cordillera during the middle Eocene

to middle Miocene times induced flexural subsidence and deposition in a foreland basin to

the east, the future Magdalena Valley and Eastern Cordillera (Gómez et al., 2005; Horton

et al., 2010b). The Miocene collision of the Panama-Choco arc (PB and CB in Fig. 1A)

with the North Andes (Duque-Caro, 1990) produced the principal phase of tectonic

inversion and shortening in the Eastern Cordillera (Van der Hammen, 1958; Cooper et al.,

1995) and separated the Llanos basin from the middle Magdalena Valley, which became

an intermontane basin (Moreno et al., 2011; Horton et al., 2015). The appearance of post–

middle Miocene alluvial sediments in the Llanos Basin has been linked to the onset of

uplift and exhumation in the Eastern Cordillera (Van der Hammen, 1958; Dengo and

Covey, 1993; Cooper et al., 1995).

2.3.2 STRATIGRAPHY

The stratigraphic units of the area can be divided into three stages, pre-Cretaceous,

Cretaceous to Paleocene, and Eocene to present day. West of the Tesalia fault,

unmetamorphosed Devonian shallow marine sedimentary rocks unconformably underly

Mesozoic synrift sediments (Fig. 2.1). During an early stage of rifting, Triassic to Jurassic

redbeds accumulated in the hanging walls of normal faults (Colletta et al., 1990). As rifting

continued, up to 5km of Early Cretaceous limestones, dolostones, shales, siltstones, and

evaporites accumulated during major marine transgressions (Branquet et al., 2002). In the

Late Cretaceous, rifting ended and broad thermal subsidence resulted in the deposition of

15

up to 3km of platform deposits. This postrift sedimentation began with the deposition of

Une Formation quartz sandstones (Fig. 2.2) in fluvial channels, bays and estuaries

(Sarmiento-Rojas et al., 2006; Petrobras, 2008). The continuous uniformly thick (~500m)

Une Formation units were overlain by the main hydrocarbon source rock, the

Gachetá/Chipaque Formation, shallow marine shales and sandstones formed in a

transitional environment during the Coniacian-Santonian (Villamil, 1999). The Gachetá

Formation includes organic-rich, occasionally phosphatic, black marine mudstones. The

Gachetá (and other time-equivalent lithostratigraphic units, including the La Luna

Formation in western Venezuela) have generated the majority of the hydrocarbons

produced in northwestern South America (Macellari and DeVries, 1987). During the early

Maastrichtian, quartz, shales and massive sandstones of the Guadalupe Group were

deposited, forming hydrocarbon reservoir rocks (Petrobras, 2008). Following a major Late

Cretaceous-Early Paleocene hiatus, fluvial-deltaic sediments were deposited, forming the

sandy Barco Formation and the more clayey Los Cuervos Formation. The Barco Formation

is an important reservoir in the Llanos basin (Cazier et al., 1995). After fluvial erosion in

the early middle Eocene, quartz sandstones and mudstones of the Mirador Formation were

deposited, the most important reservoir rock in the Llanos eastern foothills (Sánchez et al.,

2015). The top of the Mirador Formation is the boundary between the late Eocene and the

Oligocene (Sánchez et al., 2015) overlain by up to 3km of estuarine and locally marine

deposits of the Carbonera Formation (Cazier et al., 1995, 1997; Cooper et al., 1995; Bayona

et al., 2008; Parra et al., 2009a). The Carbonera Formation consists of eight informal units

(C1 to C8) of interlayered sandstone and mudstone-dominated deposits (e.g., Bogota Ruiz,

1988; Cooper et al., 1995; Parra et al., 2009b). During the middle Miocene, the Leon

16

Formation was deposited on a regional flooding surface in a continental to coastal plain

environment. Finally, during the late Miocene-Pliocene, at least 3km of fluvial gravels

interbedded with variegated floodplain units of the Guayabo Formation were deposited

during the period of most rapid uplift in the Eastern Cordillera (Cooper et al., 1995; Mora

et al., 2008).

2.3.3 STRUCTURAL GEOLOGY PREVIOUS WORK

The geologic structure of the Medina Basin and eastern foothills of the Eastern

Cordillera has been the subject of numerous regional studies (e.g., Rowan and Linares,

2000; Branquet et al., 2002; Mora et al., 2006, 2010a; Parra et al., 2009a, 2010; Jimenez et

al., 2013). In this paper we present a revised interpretation of the Guavio anticline structure

and the first geologic model for the Parrando anticline.

2.3.3.1 GUAVIO ANTICLINE

Structurally the Medina Basin contains the broad Guavio-Nazareth anticline–syncline

pair between the Tesalia thrust to the west and the Guaicaramo fault to the east (Fig. 2.1).

Rowan and Linares (2000) used 2D seismic profiles, axial surface analysis, and fold-

evolution matrices to produce a 3-dimensional model for the Guavio anticline. They

interpreted the Guavio anticline as a fault-bend fold with lateral variations in ramp height,

ramp dip, and intermediate flat length. Branquet et al. (2002) interpreted the Guavio

anticline as a basement pop-up related to dextral strike-slip faulting. Mora et al. (2006) and

Parra et al. (2009a) interpreted the Guavio anticline as a broad fault-bend fold related to

the Guaicaramo thrust that splays at depth from the Tesalia fault. The Guavio anticline

appears to be a fault-bend fold with 4-way closure and seal, but there is little or no

17

commercial hydrocarbon. To the west of the Guavio anticline, the Nazareth syncline is a

highly asymmetric, east-verging fold that formed as a result of fault-propagation folding

along the Servita/Tesalia fault system according to Parra et al. (2009a).

2.3.3.2 PARRANDO ANTICLINE

In this paper we present the first seismic images and structural interpretation for the

Parrando anticline (Fig. 2.1). According to Parra et al. (2009a), deformation in the area is

minor and results from the southward propagation of the Cusiana fault and the associated

hanging-wall La Florida anticline within en-echelon segments of the fold-thrust belt. Mora

(2007) and Parra et al. (2010) interpreted folding in the footwall of the Guaicaramo thrust

near Chaparral 1 well (Fig. 2.1) as fault-propagation folding related to movement on the

Guaicaramo thrust. Based on the absence of growth strata in seismic lines of Miocene-

Pliocene sediments in the footwall of the Guaicaramo thrust fault, Mora (2007) and Parra

et al. (2010) predicted a maximum age of 5Ma for initial thrusting along the Guaicaramo

fault.

2.3.4 PETROLEUM GEOLOGY PREVIOUS WORK

2.3.4.1 GUAVIO

Sánchez et al. (2015) used 1-D simulations to predict that oil generation from the

Chipaque Formation (Gacheta equivalent) began at the end of the Paleocene (ca. 58 Ma)

southeast of the present Eastern Cordillera (west of the Tesalia fault in Fig. 2.1) and

progressed northward. The Sánchez et al. (2015) 1D model assumed exponentially

decreasing heat flow ranging from ~63 to 33mW∕m2 associated with postrift lithospheric

thermal contraction, with an increase in the basal heat flux up to nearly 80mW∕m2 during

18

and after the Oligocene when intense mountain building (Parra et al., 2009b; Mora et al.,

2010a, 2010b) presumably caused isotherm advection and higher basal heat flux (Mora et

al., 2015). At a regional level, oil generation west of the Tesalia fault ceased abruptly

between approximately 25 and 20Ma as a result of the onset of exhumation of the Eastern

Cordillera (Parra et al., 2009b; Moraetal.,2010a). According to Sánchez et al. (2015)

locations east of the main inversion faults (Servitá, Tesalia, Pajarito), generated very little

to no oil. Between 50 and 25Ma the generation area expanded to encompass its largest

geographical extent, excluding only the easternmost locations in the present-day eastern

foothills and active foredeep depozone. During this period, the greatest volume of oil was

generated as most of the organic facies in the Chipaque Formation reached peak generation

and expulsion (Sánchez et al., 2015). 1D analysis of sediment accumulation in the Medina

Basin (Parra et al., 2010) re flects a three-stage history characterised by an Eoceneearly

Oligocene episode of slow sediment accumulation with rates of 30–70m/Myr that separates

two periods of faster accumulation during Late Cretaceous-Paleocene (100m/Myr) and late

Oligocene-Pliocene time (220m/Myr), respectively. By the early Miocene (20Ma) in

Guavio, the Chipaque organic facies was 49%–100% converted (Sánchez et al., 2015).

2.3.4.2 PARRANDO

According to the Sánchez et al. (2015) 1D models, at present there is only one local

kitchen in the eastern foothills east of the Guaicaramo fault near the Cusiana oil field (near

Rio Chitamena E−1 wellinFig.1). A 1D model by Cazier et al. (1995) showed rapid burial

of the Cusiana area under Guayabo Formation sediments. Near Cusiana, the Gachetá

Formation began to expel oil, before thrusting began, at 120°C at 8Ma (Cazieretal.,1995).

19

Figure 2.2. Stratigraphic column for Llanos foothills. The Medina-1 gamma ray log is shown on the left. The stratigraphic column is

modified from Ramon and Fajardo (2006).

20

Gas with some oil began to be expelled at 150°Cat 6Ma, immediately before thrusting

began, and continues to present day. The presence of hydrocarbons in Parrando-1 (Fig. 2.1)

confirms the presence of an active petroleum system near Parrando.

2.4 DATA AND METHODOLOGY

2.4.1 SEISMIC INTERPRETATION

Data for this study included a 3D seismic volume, (246km2 5000 msec), 70 2D seismic

lines (176km), 18 wells with caliper, gamma-ray, sonic, density logs, and checkshot

surveys. The 2D survey parameters (such as Automatic Gain Control - AGC) and datum

were adjusted to merge with the 3D survey. The surface geology maps (Fig. 2.1) were

obtained from the Colombian Geological Survey for Block 229 (Montoya et al., 2013) and

the geologic map of Colombia (Alcárcel et al, 2017). This study is based on integration of

geophysical and geological interpretation. Seismic reflection profiles provided the main

structural control for the subsurface geological interpretation constrained with available

exploration wells. The research included seismic interpretation, structural modelling, 1D

basin modeling, and data analyses. Seismic interpretation was carried out using Petrel

software, including regional seismic stratigraphy, structural maps, surface attributes and

time-depth conversion. PetroMod software was used to generate 1D basin models,

including burial history curves and source rock maturity. The Medina-1 well log was used

to identify seismic units in the Guavio anticline (Fig. 2.1). The velocity model for Medina-

1 well (Fig. 2.3a) was from a check shot survey after Parra (2008). A synthetic seismogram

(Fig. 2.3b) was generated from the well density log using 25Hz Ricker wavelets.

Identification of horizons in the 3D seismic volume southeast of the Guaicaramo fault was

based on a well tie to the Parrando-1 well (Fig. 2.1). A time depth chart for Parrando-1 was

21

based on a well check shot survey (Fig. 2.4a, after Petrobras, 2008). The sonic log was then

edited and used to produce a synthetic seismogram (Fig. 2.4b). Fig. 4b shows the Parrando-

1 Gamma ray log with formation tops after Petrobras (2008) and the good fit between the

synthetic and the 3D seismic in the lower part of the section.

2.4.2 STRUCTURAL PROFILES AND RESTORATION

Structural models were created with Move software and were constrained by seismic

and well data and surface geology. Digital elevation models (DEMs) were uploaded with

the geologic maps to construct cross sections using volume-balancing techniques (Suppe,

1983). Surface geology, topography, and well data were displayed on the seismic sections

as close to 1:1 vertical exaggeration as possible. Regions of homogeneous dip (dip

domains) and major discontinuities were identified. Spectral analysis was used to identify

fundamental step-up angles (Suppe, 1983). Stratigraphic thicknesses were determined from

surface geology, seismic, and well data, and depths to basal detachments were estimated

from the seismic profiles. The Guavio profile was then retro deformed to test the

interpretation and predict the timing of potential migration pathways and trap formation.

Eight 2D seismic profiles and the Medina-1 well were used to constrain the geologic

interpretation for the Guavio anticline. The interpretation of the Parrando anticline east of

the Guaicaramo fault presented in this paper was based on 3D seismic data and two drilled

wells (Parrando and Chaparral). Petroleum systems analysis utilized PetroMod software to

generate 1D basin models including burial history curves and source rock maturity.

22

2.5 RESULTS

2.5.1 GUAVIO

Fig. 2.5 shows an uninterpreted and interpreted seismic profile through the Guavio

anticline. The NW side of the profile is 2D line ME1981-09-MII. This line was chosen

because the seismic quality was better than the 2D dip line seismic profile passing through

Medina-1 well. The SE end of the profile is from the 3D seismic volume. The hanging wall

horizon picks are constrained by the Medina-1 well (Fig. 2.3, projected 4.2km along a

profile parallel to structural strike, Fig. 2.6). Previous formation top picks in the lower part

of the well are consistent from the Gacheta Formation to the top of Carbonera Formation.

We note however, that picks for the top of the Leon Formation vary considerably. The

footwall formation top picks are tied to the Parrando-1 well (Fig. 2.4) through the 3D

seismic volume. Apparent surface dips are from Branquet et al. (2002) and Montoya et al.

(2013). Displacement on the Cusiana fault (Fig. 2.1) dies out before intersecting this profile

(Fig. 2.5). Displacement on the Parrando fault (Fig. 2.1) also decreases to the south and is

negligible on this profile (Fig. 2.5). Fig. 2.7 extends the structural interpretation to the

northwest to the Tesalia fault showing the interpretation of Parra et al. (2009a) and the

location of the Nazareth pseudo well (this paper). The surface geology (Montoya et al.,

2013) and seismic profile clearly show that locally the Guaicaramo thrust is a bedding plane

thrust at the base of the Guadalupe Formation. Seismic reflectors dip unbroken to the north

west on the flank of the Guavio anticline showing no basement pop-up fault as proposed

by Branquet et al. (2002). Instead, we interpret the Guavio anticline as formed by

overlapping ramp anticlines. The upper fold was formed by a ramp thrust from a base Une

Formation detachment near the Lower-Cretaceous, Upper-Cretaceous unconformity to a

base Guadalupe Formation bedding plane thrust. The fault location was determined from

23

dip domain boundaries visible in the seismic profile. Beneath the upper Guavio fault-bend

fold is a basement ramp anticline leading to a bedding plane flat at the Upper Cretaceous

basement unconformity east of the Guaicaramo thrust. We interpret the basement fault as

a blind thrust or wedge fault because a minimum 5km of shortening was required to form

the basement ramp anticline with a foreland dipping limb in the footwall of the Guaicaramo

thrust. This amount of shortening is not observed in the foreland southeast of the

Guaicaramo thrust along the profile trend. Total shortening in the near by Parrando

anticline east of the Guaicaramo thrust was only about 1km. We interpret the southeast-

dipping reflectors observed in the footwall of the Guaicaramo thrust as the southeast flank

of the basement fault-bend fold. The basement ramp anticline produced 2km of relief with

5km of shortening. The upper ramp anticline produced 1.5km of relief with 14km of

shortening. Our overlapping ramp anticline interpretation for the Guavio anticline is similar

to that of Parra et al. (2009a) and Mora et al. (2010b) for a profile 14km to the south.

However, unlike the Parra et al. (2009a) and Mora et al. (2010b) profiles, we interpret the

basement fault-bend fold as formed by a ramp in pre-Cretaceous basement to a double

wedge fault that forms the southeast-dipping forelimb in the Guaicaramo thrust footwall.

The Guaicaramo footwall structure was termed the Cabuyarito anticline by Mora et al.

(2010b) and interpreted as a fault-propagation fold.

2.5.1.1 RETRODEFORMED GUAVIO CROSS SECTION

The Guavio profile was retrodeformed to late Miocene (9Ma) by flattening on the top

of the Leon Formation (Fig. 2.8A). There are no major unconformities or growth structures

in the Leon Formation or in the lower Guayabo Formation, suggesting that the first order

present structures were formed after deposition of the Leon and lower Guayabo formations

24

(late Miocene-Pliocene or younger than 7Ma). The only possible exception is thin-skinned

thrusting on the Guaicaramo thrust (Fig. 2.8D) where earlier ramp erosion would have been

subsequently removed by later uplift (see discussion of thin-skinned vs thick-skinned

deformation in section 5.1). In fact, a seismic reflection based volume balanced cross

section for the northern termination of the Guavio anticline, just 11km northeast of Medina-

1 well, clearly shows that thin-skinned thrusting preceded thick-skinned basement involved

deformation (Albesher et al., 2019). To the northwest, fault-propagation folding probably

began to occur by the middle Miocene (Parra et al., 2009a) on the Lengupa and Tesalia

faults (Fig. 2.7). Apatite and zircon fission track ages by Mora et al. (2008); Parra et al.

(2009b); Mora et al. (2010a); Mora et al. (2010b); Ramirez-Arias et al. (2012); and Mora

et al. (2013) suggest that uplift on the Tesalia fault system may have begun by early

Miocene. Conformable tight folding of Leon Formation sediments in the Nazareth syncline

forelimb of the Tesalia basement fault propagation fold (Fig. 2.7) demonstrates a maximum

late Miocene age (<9Ma) for the greatest Tesalia basement folding and uplift. The Early

and Late Cretaceous stratigraphic section thickens abruptly northwest of the Guaicaramo

fault (Fig. 2.8A) filling accommodation space produced by Early Cretaceous normal fault

extension and Late Cretaceous thermal subsidence on the Guaicaramo fault. We identify

at least three deformation events in the Neogene/ Quaternary evolution of the Guavio

structure. The first was the compressive inversion of the Guaicaramo normal fault with

800m reverse slip (Fig. 2.8B). The second event was formation of a basement ramp

anticline with 2km of relief (Fig. 2.8C). The southeast limb of this fold is observed in the

footwall block of the Guaicaramo thrust. This fold was formed by a blind double wedge

fault with over 5km of slip. We interpret this as a wedge fault, because minimal slip is

25

observed to the southeast of the wedge tip. The upper bedding plane ramp crops out as a

thin-skinned thrust at the surface. Additional bedding plane thrusting on the base

Guadalupe Formation detachment may have accommodated more than the minimum 5km

observed (Fig. 2.8D), since angular unconformities evidencing earlier thrusting would have

been eroded during subsequent basement uplift. We estimate the thickness of Early

Cretaceous units involved in the hanging wall of this basement fold as 1–3km based on the

3km thick overturned section cropping out westoftheTesalia fault (Fig. 2.7,Parraetal.,

2009a).The final eventwas the formation of the Guavio fault-bend fold with 1.5km of relief

produced by 14km of slip on the Guaicaramo ramp thrust (Fig. 2.8D). We estimate at least

20km of total Neogene/Quaternary shortening on the Guavio fold thrust system. Since

lower and middle Guayabo Formation horizons are conformably folded on both flanks of

the Guavio anticline, we conclude that the basement fault-be fold and the Guavio faultbend

fold occurred in the last 6 million years, probably 6 -3Ma during the late Miocene-Pliocene

uplift phase (e.g., Anderson et al., 2016).

2.5.2 PARRANDO

Fig. 2.9 shows an uninterpreted and interpreted seismic profile of the Parrando

anticline. The profile is merged 2D line 43BR-VN05-06 and 3D seismic inline 136. The

profile is depth corrected based on a check shot survey for Parrando-1 well (Fig. 2.4a) and

horizons were identified from the well tie at Parrando-1 (Fig. 2.4b). For location see Fig.

2.1. The geometry of the Parrando ramp anticline requires a deeper hanging wall flat and a

shallower footwall flat to form the forelimb of the fold. The listric breakthrough reverse

fault alone cannot produce the anticline. A flat-ramp-flat geometry is required. In this case,

the breakthrough reverse fault has only 200m of slip. The ramp anticline was formed by an

26

earlier 1km of slip. The position of the hanging wall flat near the base of the Carbonera is

determined by the footwall cutoffs against the fault ramp observed in the seismic profile.

In this image (Fig. 2.9) forelimb cutoffs for the ramp anticline are not

Figure. 2.3. Velocity model and well tie for Medina-1. a. Time (1WTT)-depth graph for

Medina-1 well from check-shot survey (Parra, 2008). b. Medina-1 well tie, using a

synthetic seismogram and 2D seismic profile MVI-1997-1870-MII. For location see Fig.

2.1

27

Figure. 2.4. Time-depth relationship and well tie for Parrando-1. a. Time (TWT)-depth

graph for Parrando-1 from a well check shot survey (Petrobras, 2008). b. Parrando-1 well

tie with 3D seismic (inline 139) showing the good fit in the lower part of the section.

Gamma ray log with formation tops is shown on the left (after Petrobras, 2008). Amplitude,

power spectrum, and phase spectrum are shown for the zero-wave wavelet used to create

the synthetic seismogram. Gamma ray log (for color explanation see Fig. 2.2). (For

interpretation of the references to color in this figure legend, the reader is referred to the

Web version of this article.)

28

clearly observed in the footwall, but the position of the footwall flat in the middle

Carbonera Formation is indicated by the intersection of the fault ramp and the hinge axis

for the gentle forelimb dip domain observed in the hanging wall. We interpret the apparent

discrepancy between the hanging wall versus the footwall thickness of the Carbonera

Formation as stratigraphic, predating the Parrando anticline, and perhaps serving to initiate

the ramp location. The Parrando anticline is a gentle faultbend fold (200m relief) with a

small break through fault in the forelimb. The structure was produced by 1.2km of total

shortening. Conformable folding of the Guayabo Formation produced by 1.2km of total

shortening. Conformable folding of the Guayabo Formation above the Leon Formation

indicates that the Parrando anticline is very young, and probably formed in the last 3 Myr.

A separate smaller fault-bend fold also deformed the Mirador reservoir rocks in the

footwall. Several vertical faults in the footwall show normal offsets that may be produced

by lithospheric loading or minor out-of-plane dextral shear. Spectral decomposition

(Continuous Wavelet Transformation) and seismic multi-attribute analysis were used to

detect fluvial systems in the Parrando footwall (Saeid et al., 2018). The results suggest new

potential stratigraphic plays in meandering channels and over bank deposits. In addition, a

distinct change in river drainage directions during the deposition of Carbonera (C5) may

reflect early Miocene (~20Ma) uplift of the nearby mountain front possibly related to

thinskinned thrusting on the Guaicaramo fault (Saeid et al., 2018).

29

Figure. 2.5. Uninterpreted and interpreted seismic profiles of the Guavio anticline and Guaicaramo thrust. Horizontal and vertical

scales are approximately equal. See Fig. 2.1 for profile location.

30

Figure. 2.6. Uninterpreted and interpreted seismic profile parallel to structural strike of the Guavio anticline. Horizontal and vertical

scales are approximately equal. See Fig. 2.1 for profile location.

31

2.5.3 HYDROCARBON MATURATION AND MIGRATION

Burial and thermal histories were constructed for Medina-1, Parrando, and a Nazareth

pseudo-well using PetroMod thermal modeling software. The present-day heat flow was

estimated from boreholecorrected downhole temperatures and from regional paleo heat-

flow estimates (INGEOMINAS-ANH, 2008). The heat flow used for the foreland burial

history was 35–46mW/m2, typical for foreland basins worldwide. From these histories,

timing of hydrocarbon charge may be inferred.

2.5.3.1 NAZARETH PSEUDO-WELL AND MEDINA-1

We located a Nazareth pseudo-well in the deepest Gacheta/ Chipaque formation

source rock in the Nazareth syncline 17km southwest of Medina-1 well (Figs. 2.1 and 2.7)

in order to estimate the maximum local potential source rock maturity in the Medina basin

to the present. Burial rates increased about 35Ma with the deposition of the Carbonera

Formation accumulating 3.6km of sediment in 20Myrat an average rate of 0.18mm/yr. At

23Ma the deposition rate increased to 0.38mm/yr (Parra et al., 2009a). 1-D modelling based

solely on the Medina-1 well underestimates the source rock burial depths by 1km thinning

of the Carbonera Formation eastward (Silva et al., 2013) plus the thickness of the Guayabo

Formation rocks eroded during the folding of the Guavio anticline. A total maximum pre-

erosion thickness of Guayabo Formation of 1900 m was used for the reconstruction. We

assumed thrusting was initiated at 3Ma. Erosion began immediately after thrusting and

continues to present day. Theheat flowsassumedfor the burial history were 35–46mW/m2

(35mW/m2 shown in Fig. 2.10) typical values for foreland basins. Similar heat flows were

reported for the Llanos basin by Bachu et al. (1995) and used by Cazier et al. (1995) for

their Cusiana 1-D model. The Sánchez et al. (2015) 1D model assumed exponentially

32

Figure. 2.7. Extended profile for Fig. 2.5 to the northwest showing the Tesalia fault and Nazareth syncline (after Parra et al., 2009a)

and the location of the Nazareth pseudo well (this paper). Note the 11km offset between the profiles. See Fig. 2.1 for profile locations.

33

decreasing heat flow ranging from ~ 63 to 33mW∕m2 associated with postrift lithospheric

thermal contraction, but a veraging 46mW∕m2 for the last 60 Myr west of the Tesalia fault.

In the Medina basin, our 1D burial model for the Nazareth syncline pseudo-well predicts

that the Gachetá Formation began to expel oil at a depth of 4.4km and temperature of 120°C

at 24-18Ma (Fig. 2.10b), depending on the heat flow, but 12–18 Myr before the Guavio

trap formed. The Medina-1 1-D model predicts that the Gachetá Formation began to expel

oil at 4.3km depth and 120°C at 21-12Ma (Fig. 2.10a) but underestimates the source rock

burial depths by the eastward thinning Carbonera Formation plus the thickness of the rocks

eroded during Guavio anticlinal folding and uplift.

2.5.3.2 NAZARETH PSEUDO-WELL AND MEDINA-1

We located a Nazareth pseudo-well in the deepest Gacheta/ Chipaque formation

source rock in the Nazareth syncline 17km southwest of Medina-1 well (Figs. 2.1 and 2.7)

in order to estimate the maximum local potential source rock maturity in the Medina basin

to the present. Burial rates increased about 35Ma with the deposition of the Carbonera

Formation accumulating 3.6km of sediment in 20Myrat an average rate of 0.18mm/yr. At

23Ma the deposition rate increased to 0.38mm/yr (Parra et al., 2009a). 1-D modelling based

solely on the Medina-1 well underestimates the source rock burial depths by 1km thinning

of the Carbonera Formation eastward (Silva et al., 2013) plus the thickness of the Guayabo

Formation rocks eroded during the folding of the Guavio anticline. A total maximum pre-

erosion thickness of Guayabo Formation of 1900 m was used for the reconstruction. We

assumed thrusting was initiated at 3Ma. Erosion began immediately after thrusting and

continues to present day. Theheat flowsassumedfor the burial history were 35–46mW/m2

(35mW/m2 shown in Fig. 2.10) typical values for foreland basins. Similar heat flows were

34

reported for the Llanos basin by Bachu et al. (1995) and used by Cazier et al. (1995) for

their Cusiana 1-D model. The Sánchez et al. (2015) 1D model assumed exponentially

decreasing heat flow ranging from ~ 63 to 33mW∕m2 associated with postrift lithospheric

thermal contraction, but a veraging 46mW∕m2 for the last 60 Myr west of the Tesalia fault.

In the Medina basin, our 1D burial model for the Nazareth syncline pseudo-well predicts

that the Gachetá Formation began to expel oil at a depth of 4.4km and temperature of 120°C

at 24-18Ma (Fig. 2.10b), depending on the heat flow, but 12–18 Myr before the Guavio

trap formed. The Medina-1 1-D model predicts that the Gachetá Formation began to expel

oil at 4.3km depth and 120°C at 21-12Ma (Fig. 2.10a) but underestimates the source rock

burial depths by the eastward thinning Carbonera Formation plus the thickness of the rocks

eroded during Guavio anticlinal folding and uplift.

2.5.3.3 PARRANDO 1D MODEL

Southeast of the Guaicaramo fault at Parrando-1 well, we estimated the burial

history with a 1-D model (Fig. 2.10c), assuming a total maximum pre-erosion thickness of

Guayabo and Leon formations of 3600m. The heat flow assumed for the Parrando 1-D

burial history was 35mW/m2, a typical value for a foreland basin, and within the range of

values used by Cazier et al. (1995) for their Cusiana 1-D model. In Parrando, the model

predicts that the Gachetá Formation began to expel oil at 120°C at 7Ma (Fig. 2.10c), just

prior to Andean trap formation. Near Cusiana, Cazier et al. (1995)Cazier et al. (1995)

obtained very similar results predicting that the Gachetá Formation began to expel oil at

8Ma and 120°C, which was just before folding and thrusting began. Our burial model

predictions are also similar to 1-D models by Albesher et al. (2019) for Bromelia-1 and

Rio Chitamena E−1 wells to the northeast along the La Florida anticline structural strike

35

(Fig. 2.1). The presence of hydrocarbons in C5 in Parrando-1 confirms the presence of an

active hydrocarbon migration system and suggests the potential for Carbonera oil

accumulations (Petrominerales, 2009). Four sandstone intervals at the base of C5

encountered oil shows. In general, the porosity and permeability are relatively low, the

maximum porosity is about 10–12% and the permeability ranges from 15 to 60 md.

2.5.3.4 PETROLEUM SYSTEM EVOLUTION, SOURCE PODS, EXPULSION,

AND TRAP FORMATION

The three schematic maps in Fig. 2.11 show the evolution of the petroleum systems in

the Medina basin and Parrando foreland basin over the last 18 Myr. We use published

isopachs (Silva et al., 2013), our new 1-D burial models, and new backstripped isopachs

from the Parrando 3-D seismic volume to predict source pod locations, migration

pathways, and trap locations. Depths to Gacheta Formation source rocks are estimated from

1-D models for the Nazareth pseudo-well, Medina-1, and Parrando-1 wells (this paper),

and for Bromelia-1 and Rio Chitamena E−1 wells (Albesher et al., 2019). Parrando area

maps show contour trends for depth to Gacheta Formation after stripping off sediment

layers at 18Ma (Fig. 2.11a), 7Ma (Fig. 2.10b), and Present (Fig. 2.10c). At 18Ma (Fig. 11a)

the Nazareth source pod began expulsion southeastward toward the Llanos. However, the

Guavio anticlinal trap had not formed, so hydrocarbons continued updip toward the Llanos.

The timing of initial compressive inversion of the Guaicaramo Lower Cretaceous age

normal fault is uncertain. Saeid et al. (2018) interpret an abrupt change in stream flow

directions in C-5 to indicate the rise of incipient foothills in the area of the Guaicaramo

thrust at about 22Ma. In a seismic reflection profile from the Medina basin 27 km south

west of Medina-1, Teixell et al. (2015) noted an angular unconformity in the lower

36

Carbonera Formation truncating deep thrust-related folds in the core of the Guavio

anticline. A compilation of radiometric age data for the Medina -foothills area (Albesher

et al., 2019) suggests initial uplift on the Tesalia fault at 25Ma, and uplift on the

Guaicaramo at 12-8Ma and 4Ma to present.

Based on the absence of growth strata in Miocene Pliocene sediments in the footwall

of the Guaicaramo thrust fault, Mora (2007) and Parra et al. (2010) predicted a maximum

age of 5Ma for initial thrusting along the Guaicaramo fault. In any case, at 18Ma

hydrocarbons either migrated updip to the Llanos or escaped to the surface on an early thin-

skinned Guaicaramo thrust ramp. At 7Ma (Fig. 2.11b) the Guavio structural trap began to

form, but most of the Nazareth-Medina hydrocarbon was already expelled.

Hydrocarbon generation began in the eastern foothills southeast of the Guaicaramo

fault at about 8–7Ma as source rocks were rapidly buried by Guayabo Formation

sediments. At present (Fig. 2.11c) eastward and southeastward hydrocarbon generation

continues from the Cusiana source pod southeast of the Guaicaramo fault. The Guaicaramo

fault effectively seals the Medina basin from the active hydrocarbon sources in the eastern

foothill.

37

Figure. 2.8. Retro-deformed cross section for Guavio anticline (Fig.2.5). For location, see

Fig. 1. No vertical exaggeration. A: late Miocene (before 9Ma), B: inversion of

Guaicaramo normal fault, C: Pliocene (post 6Ma) blind fault-bend-fold double wedge fault,

D: 2nd fault-bend fold, present day, E: alternative model with bedding plane thrusting

preceding formation of the basement ramp anticline.

38

Figure. 2.9. Uninterpreted and interpreted seismic profiles of Parrando anticline, left: 2D

line 43BR-VN05-06, right: 3D seismic inline 136. Tops of formations are indicated. The

profile is depth corrected from Parrando-1 check shot survey, no vertical exaggeration.

For location see Fig. 2.1.

39

2.6 DISCUSSION

2.6.1 THIN-SKINNED VERSUS THICK-SKINNED DEFORMATION

While this study does not confirm that thin-skinned thrusting preceded thick-

skinned basement deformation, it does not rule it out as stratigraphic evidence for an

unconformity related to thin-skinned ramp thrusting on the Guaicaramo thrust would have

been removed by erosion during Pliocene basement uplift (Fig. 2.8c and e). Dengo and

Covey (1993) proposed that the Eastern Cordillera is essentially an east-verging structure

formed during two main tectonic phases. The first tectonic phase induced a thin-skinned

style that created large, east-verging thrust faults, detached into Lower and Upper

Cretaceous and Paleogene sequences, with the greatest shortening in the middle-Miocene

to Pliocene. During the Pliocene, deformation changed from basement-detached to

basement involved as Jurassic and Early Cretaceous normal faults were inverted (Dengo

and Covey, 1993). There are various estimated ages for the initiation of thin-skinned

thrusting in the Eastern Cordillera. Corredor (2003) estimated over 50km of Oligocene

ENE-WSW shortening in the northern Eastern Cordillera. The Oligocene age deformation

is defined in the present eastern foothills area by the base of Carbonera (C6) unconformity,

marking an important stage of Cenozoic crustal shortening in the pre-Eastern Cordillera

foreland basin (Corredor, 2003; Martinez, 2006; Egbue and Kellogg, 2012). In a seismic

reflection profile from the Medina basin 27km southwest of Medina-1, Teixell et al. (2015)

also noted an angular unconformity in the lower Carbonera Formation truncating deep

thrust-related folds in the core of the Guavio anticline. The lower Carbonera Formation

angular unconformity is also visible in our seismic profile parallel to strike of the Guavio

anticline (Fig. 2.6). Saeid et al. (2018) interpret an abrupt change in stream flow directions

in Carbonera (C-5) to indicate the rise of incipient foothills in the area of the Guaicaram

40

Figure. 2.10. Burial histories for source rocks (Gacheta/Chipaque Formation) assuming

constant heat flow of 35mW/m2, (A) Medina-1, (B) Nazareth PW (C) Parrando-1.

41

Figure. 2.11. Petroleum system evolution for Medina basin and adjacent Parrando anticline

showing estimated depths for source rocks (Gacheta/Chipaque formations) and migration

pathways. 1D models for Medina, Parrando, and Nazareth pseudo well (this study). 1D

models for Bromelia and Rio Chitamena wells (Albesher et al., 2019). A: 18Ma– Nazareth

source pod begins expulsion southeast toward Llanos. B:7Ma –Guavio trap begins to form,

but much of HC has already been expelled. C: Present – expulsion continues southeast of

the Guaicaramo fault.

42

thrust at about 22Ma. Structural reconstructions by Jimenez et al. (2013) and Mora et al

(2010a, 2010b) show short wavelength late Oligocene to middle Miocene folding that

suggests thinskinned deformation. Sediment provenance data also show a late Oligocene-

early Miocene timing of exhumation of these structures (Horton et al.,2010b;Bande etal.,

2012).A compilation ofradiometric age data for the Guavio-foothills area (Albesher et al.,

2019) suggests initial uplift on the Tesalia fault at 25Ma, and uplift on the Guaicaramo at

128Ma and 4Ma to present. To the south in the Garzón Massif, early to middle Miocene

thinskinned imbricate thrusting over basement rocks resulted in approximately 43km of

shortening (Saeid et al., 2017; Wolaver et al., 2015) contemporaneous with the uplift of the

southern Central Cordillera (~16-9Ma) (Villagómez and Spikings, 2013). The thin-skinned

thrusting was followed by an out-of-sequence late Miocene (6Ma to present) Laramide-

style thick-skinned basement-uplift of the range which produced much of the structural

relief of the Eastern Cordillera (Dengo and Covey, 1993; Garcia, 2008; Mora et al., 2010a;

Egbue and Kellogg, 2012) and the Garzón Massif (Saeid et al., 2017). The authors note

that there are geometric and kinematic linkages between some ramp-flat structures and

basement-involved structures in the Eastern Cordillera that show that they may have a

shared or hybrid heritage. Prior to the basement Laramide orogeny in the U.S. Rocky

Mountains, the region was the site of a Cordilleran foreland basin associated with thin-

skinned deformation and flexural loading of a foldand-thrust belt. Subsequent thick-

skinned deformation (Laramide orogeny) partitioned the regional foreland basin and

caused more than 4km of localized exhumation of crystalline basement blocks,

accompanied by localized subsidence of intermontane basins. It is generally accepted that

the switch of deformation style from thin-skinned to thick-skinned was caused by the

43

change from normal high-angle subduction to low-angle subduction of buoyant Farallon

oceanic lithosphere beneath western North America (e.g., Saleeby, 2003; DeCelles, 2004;

Liu et al., 2008; Fan and Carrapa, 2014). Early-to-middle Miocene thin-skinned imbricate

thrusting over the Garzón Massif basement rocks (Saeid et al., 2017; Wolaver et al., 2015)

as well as in the Eastern Cordillera was roughly contemporaneous with the uplift of the

southern Central Cordillera (~16-9Ma) (Villagómez and Spikings, 2013) as well as the

northward advance of arc volcanism and “normal” high angle Nazca subduction (Kellogg

et al., 2019). A spike in volcanic arc activity in the Choco terrane and just east of the terrane

from 15 to 5Ma (Gómez-Tapias et al., 2013) brackets the initial Panama-Choco-North

Andes (PB and CB and NAB in Fig. 1A) collision. Five million years ago, volcanic activity

abruptly ended again north of 5.5°N as the subducting Nazca lithosphere underthrust the

shallow dipping retreating Caribbean slab (Taboada et al., 2000). Across the northern

Andes, basement blocks were rapidly uplifted 7–12km in the last 10 Myr, including the

Venezuelan Andes, Sierra de Perija, Santander Massif, Eastern Cordillera, Garzon Massif,

and the Santa Marta Massif (Fig.1A; see Kellogg et al., 2019 for references). The spatial

distribution of these numerous Laramide-style basement block uplifts correlates with

buoyant Caribbean low-angle to flat slab subduction and resultant low heat flow. The

timing (last 10 Myr), spatial distribution and orientation, and high rates of shortening (5–

15mm/yr) and uplift (0.5–1.0mm/yr) also suggest that the uplifts were accelerated by the

Panama-Choco—North Andes arc-continent collision and accretion, especially the Eastern

Cordillera of Colombia (e.g., Egbue et al., 2014)

44

2.7 CONCLUSIONS

To the northwest of Medina basin, fault-propagation folding probably began to

occur by the middle Miocene on the Lengupa and Tesalia faults. Radiometric age data for

the Guavio-foothills area by Mora et al. (2008); Parra et al. (2009b); Mora et al. (2010a);

Mora et al. (2010b); Ramirez-Arias et al. (2012); and Mora et al. (2013) suggest initial

uplift on the Tesalia fault at 25Ma, and uplift on the Guaicaramo at 12-8Ma and 4Ma to

present. Most of the Guavio deformation results from repeated inversion of the Mesozoic

Guaicaramo basin-bounding normal fault. The Guavio structure was formed by

overlapping fault-bend folds during late Miocene-Pliocene age (6-3Ma) shortening. A thin-

skinned bedding plane thrust fault may have preceded the Guavio anticline ramping to the

surface along the Guaicaramo fault. A seismically constrained volume-balanced cross

section for the northern termination of the Guavio anticline, northeast of Medina-1 well,

shows that thin-skinned thrusting pre ceded thick-skinned basement involved deformation

(Albesher et al., 2019). Unlike previous interpretations, we interpret the basement fault

bend fold as formed by a ramp in pre-Cretaceous basement that transfers slip to the

Guaicaramo thrust by a wedge fault forming a south east dipping forelimb in the footwall.

We interpret the basement fault as a blind thrust or wedge fault because of minimal

shortening observed southeast of the Guaicaramo fault. We estimate at least 20km of total

Neogene/Quaternary shortening and 2.5km of structural relief on the Guavio fold thrust

system. Our 1D basin model for the Medina-1 well suggests that the Gacheta Formation

source rocks began to expel oil at 18Ma, at least 11 Myr before trap formation at 7Ma.

Thus, hydrocarbons either migrated updip to the Llanos or escaped to the surface along the

thin-skinned Guaicaramo thrust ramp prior to Guavio trap formation. The Parrando

anticline is a gentle fault-bend fold southeast of the Guaicaramo fault with a small break

45

through fault in the forelimb. The fold began as a ramp anticline within the Carbonera

Formation with about 1km of slip. Subsequently the ramp broke through the forelimb to

the surface with 200m of displacement. Conformable folding of the Guayabo Formation

above the Leon Formation indicates that the Parrando anticline is very young, and probably

formed in the last 3 Myr. A separate smaller fault-bend fold also deformed the Mirador

reservoir rocks in the footwall. Several vertical faults in the footwall show normal offsets

that may be produced by lithospheric loading or minor out-of-plane dextral shear. The

small fault-bend fold in the footwall of the Parrando thrust appears to have 4-way closure

forming a Mirador Formation trap, and 1D models suggest hydrocarbon generation in a

source pod southeast of the Guaicaramo fault from 8 to 5Ma, similar to the Cusiana system.

However, high-angle normal and transpressive faults may have permitted hydrocarbon

escape. At present, the Guaicaramo fault effectively seals the Medina basin from the active

hydrocarbon sources in the eastern foothills. The timing of thick-skinned and thin-skinned

deformation, and trap formation were thus critical factors in the evolution of the Medina

and Cusiana petroleum systems. Hydrocarbon expulsion preceded formation of the Guavio

anticlinal trap by 11–15 Myr, while the critical moment and trap formation were

synchronous for the Cusiana system. Generation and trap timing were favorable for the

small Parrando footwall structure, but abundant fractures formed escape pathways. The

presence of hydrocarbons in C5 in Parrando-1 confirms the presence of an active

hydrocarbon system and suggests the potential for Carbonera Formation oil accumulations.

46

CHAPTER III

3D SEISMIC ATTRIBUTES ANALYSIS OF SUBSURFACE FAULT

AND FRACTURE SYSTEMS FOR PARRANDO ANTICLINE, LLANOS

FOOTHILLS COLOMBIA

3.1. OVERVIEW

Previous studies of fractures in the Foothills of the Eastern Cordillera Colombia have

relied on surface geologic studies or downhole imager logs. In this study we used attribute

analysis and ant-tracking algorithms on a 3D seismic volume (246 km² 5000 msec) to

produce a new 3D fault model, seismic attribute analysis, curvature, and fracture network

maps for the Parrando anticline. We then use the fracture patterns to predict relative ages

and directions of regional stresses. We found two prominent fracture systems, NE-SW and

NW-SE. The major fracture strike azimuth is NE-SW (040 ± 15°) parallel to the structural

trend of the Foothills and is especially concentrated in the folded rocks of the Parrando

anticline. Several NE-SW fractures show extensional displacement consistent with folding

in the hanging wall or an elastic plate subjected to pure bending in the footwall. NE-SW

fractures in the Gatcheta Fm source rocks may have been inherited from Early Cretaceous

rifting, while those in the Oligocene Carbonera Fm may have been early folding or bending

of the lithosphere before the advancing mountain front. The secondary fracture strike

azimuth is NW-SE (135 ± 10°) perpendicular to the structural trend of the Foothills. The

NW-SE fractures results from a vertical intermediate stress and maximum compressive

47

stress parallel to the dip direction of bedding. NW-SE fractures are found in strata from

Miocene (21 Ma) to Pliocene (6 Ma) and are most intense in mid-Miocene strata (14 Ma).

The NW-SE fracture set may be inherited from the earlier initial folding and thrusting in

the nearby Guavio anticline and Guaicaramo thrust fault. This method permits the mapping

of fracture systems in rock volumes between wells, and in areas where no well borehole

imagery logs are available.

KEYWORDS: Parrando anticline, Fracture system, orientation, Ant tracking, 3D attribute

analysis. Time slice.

3.2. INTRODUCTION

The Parrando anticline is a low relief fault-bend fold located southeast of the Guaicaramo

fault in the Eastern Cordillera foothills (Fig. 3.1; Hafiz et al., 2019). The eastern foothills

of contain important oil fields in a complex foreland fold and thrust belt (e.g., Cazier et al.,

1995; Cooper et al., 1995). The main reservoirs of the giant Cusiana oilfield to the

northeast, the Mirador, Barco, and Guadalupe formations have low porosity but are highly

fractured in the fold traps (Cazier et al., 1995; Tamara et al., 2015). Fracture systems are

critically important, creating fracture porosity as well as pathways for hydrocarbon

migration and production (Cazier et al., 1995; Ortiz et al., 2008a; Engelder and Uzcategui,

2009; Tamara et al., 2015). Previous studies of fracture systems in the Eastern Cordillera

Foothills related their distribution to fold types and geometries based on field mapping and

subsurface borehole imager logs.

In this study we used attribute analysis (Chopra and Marfurt, 2007) and ant-tracking

algorithms (Randen et al., 2001) on a 3D seismic volume (246 km² 5000 msec) to produce

48

a new 3D fault model, seismic attribute analysis, curvature, and fracture network maps for

the Parrando anticline. Because this method allows us to map fracture-set orientations in

an entire sedimentary section, we can infer the differential stresses that were active during

their propagation through time (Engelder and Geiser, 1980). We can also sample fractures

in folded rock units as well as non-folded ones and thereby test fold models for fracture

initiation (e.g., Stearns, 1968). The attribute analysis method opens up the possibilities to

map fracture systems in rock volumes between wells, and in areas where no well borehole

imagery logs are available.

49

Figure. 3.1. Location map of the study area, on a small map. A large structure map shows

a 3D survey used for this research. Moreover, Important well in the area and three

seismic profile location.

3.3. GEOLOGIC SETTING

3.3.1. STRATIGRAPHY

During Triassic to Early Cretaceous time, the present area of the Eastern Cordillera was

an extensional basin system (Colletta et al., 1990; Jaillard et al., 1990; Cooper et al., 1995

Mora et al., 2006; Sarmiento-Rojas et al., 2006). Triassic to Jurassic redbeds accumulated

in the hanging walls of normal faults (Colletta et al., 1990) followed by up to 5 km of Early

Cretaceous limestones, dolostones, shales, siltstones, and evaporites (Branquet et al.,

2002). In the Late Cretaceous, rifting ended and broad thermal subsidence resulted in the

deposition of up to 3 km of platform deposits. This postrift sedimentation began with the

50

deposition of Une Formation quartz sandstones (Fig. 3.2) in fluvial channels, bays and

estuaries (Saeid et al., 2018).

During the Coniacian-Santonian global sea-level rise (Haq et al., 1987; Villamil, 1999)

the foremost hydrocarbon source rocks in the Foothills, shallow organic rich marine shales

and sandstones of the Gachetá Formation were deposited. This period generated the

majority of the hydrocarbons produced in northwestern South America (Macellari and

DeVries, 1987). Regression of the sea level during the early Maastrichtian led to

accumulation of quartz, shales, and massive sandstones of the Guadalupe Group

hydrocarbon reservoir rocks (Linares et al., 2009; Petrobras, 2008). Following a major Late

Cretaceous-Early Paleocene hiatus, fluvial-deltaic sediments were deposited, forming the

sandy Barco Formation and the more clayey Los Cuervos Formation. The Barco Formation

is an important reservoir in the Llanos basin (Cazier et al., 1995). After fluvial erosion in

the early middle Eocene, quartz sandstones and mudstones of the Mirador Formation were

deposited, the most important reservoir rock in the Llanos eastern foothills (Sánchez et al.,

2015). The Mirador Formation accumulated in two phases interrupted by a regional

unconformity (Martinez, 2006) with thickness decreasing eastward toward the Llanos

Basin (Cooper et al. 1995). The top of the Mirador Formation is the boundary between the

late Eocene and the Oligocene (Sánchez et al., 2015) overlain by up to 3 km of estuarine

and locally marine deposits of the Carbonera Formation (Cazier et al., 1995, 1997; Cooper

et al., 1995; Bayona et al., 2008; Parra et al., 2009a). The Carbonera Formation consists of

eight members (C1 to C8) of interlayered sandstones and mudstone-dominated deposits

described as maximum flooding surfaces (Bogota-Ruiz, 1988; Cooper et al., 1995; Parra

et al. 2009b). The odd numbers are sandstones and even numbers are mudstones (Bogota-

51

Ruiz, 1988; Jaramillo et al., 2009; Parra et al. (2009b). During the middle Miocene, the

Leon Formation was deposited on a regional flooding surface in a continental to coastal

plain environment. Finally, during the late Miocene-Pliocene, at least 3 km of fluvial

gravels interbedded with variegated floodplain units of the Guayabo Formation were

deposited during the period of most rapid uplift in the Eastern Cordillera (Cooper et al.,

1995; Mora et al., 2008).

3.3.2. STRUCTURAL GEOLOGY PARRANDO ANTICLINE

The structural geology of the eastern foothills has been described by Cazier et al.

(1995), Branquet et al. (2002), Toro et al. (2004), Parra et al. (2009a), Mora et al. (2010b),

Jimenez et al. (2013), Mora et al. (2013), Egbue et al. (2014), Teixell et al. (2015), and

Carrillo et al. (2016). Parrando anticline (Fig. 3.1) is located on the trend of anticlinal traps

associated with the Yopal-Cusiana fault system, including La Florida and Rio Chitamena

40 km to the northeast and the giant Cusiana oilfield 55 km to the northeast (Cazier et al.,

1995).Cooper et al. (1995) and Cazier et al. (1995) interpreted the Cusiana fault as a listric

reverse fault involving Early Cretaceous and older basement. Figure 3.3 shows

uninterpreted and interpreted Cusiana seismic line CU-92-03 (Cazier et al., 1995). Note

that the solution does not explain the Cusiana anticline. Mora et al. (2010) interpreted La

Florida anticline as produced by slip on the Cusiana fault, also a listric high angle reverse

fault. Albesher et al. (2019) reinterpreted the thrusting on the Cusiana fault and La Florida

anticline as thin-skinned and presented a retrodeformed model for La Florida anticline,

proposing a previously unrecognized late Miocene-Pliocene fault-bend fold formed by a

thin-skinned thrust ramping up from a mid-Cretaceous detachment (Fig. 3.4). This was

52

followed by displacement on the Cusiana reverse fault, a forelimb breakthrough fault

ramping up from two bedding plane faults. Total late Miocene-Pliocene shortening on the

La Florida anticline was about 5.7 km (Albesher et al., 2019).

According to Parra et al., (2009a), deformation in the area of the Parrando anticline

(Fig. 3.1) is minor and results from the southward propagation of the Cusiana fault and the

associated hanging-wall La Florida anticline within en-echelon segments of the fold-thrust

belt. Mora (2007) and Parra et al. (2010) interpreted folding in the footwall of the

Guaicaramo thrust near Chaparral-1 well (Fig. 3.1) as fault-propagation folding related to

movement on the Guaicaramo thrust. Hafiz et al. (2019) published the first geologic cross-

section of the Parrando anticline and interpreted it as a low relief fault-bend fold with a

small break through fault in the forelimb (Fig. 3.5). The fold began as a ramp anticline (fault-

bend fold) within the Carbonera Formation with about 1 km of slip. Subsequently the ramp broke

through the forelimb to the surface with 200 m of displacement. Conformable folding of the

Guayabo Formation above the Leon Formation indicates that the Parrando anticline is very young,

and probably formed in the last 3 Myr (Hafiz et al., 2019). The Parrando structure was produced

by 1.2 km of total shortening.

3.3.3. FRACTURE ANALYSIS – FOOTHILLS.

Fracture systems are critically important, creating fracture porosity as well as pathways

for hydrocarbon migration and production (Cazier et al., 1995; Ortiz et al., 2008a; Engelder

and Uzcategui, 2009; Tamara et al., 2015). Most of the tight, well-cemented reservoirs,

like those in the flanks of the Eastern Cordillera, have natural fractures which are important

features that control fluid-reservoir dynamics (Egbue et al., 2014). Natural fractures are

53

Figure. 3.2. Stratigraphic column for the Llanos foothill Fm using Parrando 1-st-1 well.

Showing biozones, Gamma-ray, Depth, and sequence stratigraphy (Saeid, E. 2018). See

(Fig 3.1) for location.

54

2014). Natural fractures are typically present in all rocks to varying degrees. In fold and

thrust belt regions, the rocks are even more intensely fractured. These fractures are

developed and/or modified during deformation in well consolidated rocks.

Subsequent stress regimes can strongly affect the permeability of ancient fractures that

formed in a different, older stress regime. The propagation paths for fractures in a geologic

setting are strongly influenced by the state of stress and are only weakly dependent on the

rock fabric (Olson and Pollard, 1989). Vertical fractures propagate normal to the least

principal stress, thus, they follow the path of the stress field present at the time of their

propagation (Engelder and Geiser, 1980). By examining a map of fracture-set orientation,

we can infer the differential stress that was active during their propagation. In the Cupiagua

hydrocarbon field on the eastern flank of the Eastern Cordillera north of Cusiana, cores and

image logs (Ultrasonic Borehole Imager-UBI and Fullbore Formation MicroImager-FMI)

show that natural fractures are present at different stratigraphic intervals including the main

reservoirs (Egbue et al., 2014). The mean fracture density varies within the reservoir units,

and ranges between 0.11 and 0.62 fractures per foot (Adams et al., 1999). A fracture dip

vs depth plot from UBI for the wells (Fig. 3.6) shows that most of the natural fractures

present in the reservoir between 12,000 and 16,000 ft are steeply dipping to subvertical

(40-90º) suggesting that the maximum principal stress directions are subhorizontal. In

Cupiagua, a NW-SE trending fracture set is widespread throughout the field and is

dominant in the southern portion of the field.

Tamara et al. (2015) studied the fracture systems in the foothills based on field mapping

of outcrops to determine the relative timing of fracture sets, as well as using subsurface

55

borehole imager logs for the Cusiana, Cupiagua, and Piedemonte oil fields. Using

subsurface well data. they divided the Cusiana anticline into three segments, documented

four fracture systems (NE-SW, NW-SE, E-W, and N-S) and related their distribution and

intensity to fold geometry and folding mechanism. They noted that the NE-SW fracture set

was present everywhere in the Cusiana reservoir rocks with high intensities in the hinge

region of the anticline. They also correlate the general fracture distribution with changes

in structural style in the Cusiana anticline along strike. In this study we used attribute

analysis and ant-tracking algorithms on a 3D seismic volume. This method allows us to

map fracture-set orientations in an entire sedimentary section sampled by 3D seismic. We

can map fracture systems in rock volumes between wells and in areas where no well

borehole imagery logs are available.

56

Figure. 3.3. Uninterpreted and interpreted seismic profiles of the Cusiana structure. Throw

the Cusiana 4 and Cusiana 2A wells. See Fig. 1 for profile location. (Cazier 1995).

57

Figure. 3.4. Uninterpreted and interpreted seismic profile of Rio-Chitamena structure.

Show less deformed section than the Cusiana profile. Horizontal and vertical scales are

approximately equal. See Fig. 3.1 for the profile location. (Albesher et al., 2018).

58

Figure. 3.5. Uninterpreted and interpreted seismic profiles of Parrando anticline, left: 2D

line 43BR-VN05-06, right: 3D seismic inline 136. Tops of formations are indicated. The

profile is depth corrected from Parrando-1 check shot survey, with no vertical

exaggeration. For the location, see Fig. 3.1

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3.4. DATA AND WORKFLOW

3.4.1. 3D SEISMIC VOLUME

This study used a 3D seismic survey (246 km² 5000 msec), 70 2D seismic lines (176

km), and 18 wells with caliper, gamma-ray, sonic, density logs, and checkshot surveys.

The 2D survey parameters (such as Automatic Gain Control - AGC) and datum were

adjusted to merge with the 3D volume. Surface geology maps were obtained from the

Colombian Geological Survey for Block 229 (Montoya et al., 2013) and the geologic map

of Colombia (Alcárcel and Gómez, 2017). In this paper, we focused on the Parrando

anticline in the Llanos foothills, where we used 3D seismic attribute analysis to visualize

subsurface faults and fractures. Petrel software was used to view data, analyze, and

interpret fractures. We cropped the 3D seismic volume above 1100 msec (Guayabo Fm)

and below 3400 msec (Une Fm) to eliminate artifacts introduced from basement and

surficial weathering layers (Fig. 3.6). We were particularly interested in fractures in

Mirador Fm reservoir rocks, and Carbonera Group, and Leon and Guayabo formations.

We also divided the seismic volume into folded hanging wall rocks to the northwest and

non-folded footwall rocks to the southeast (Fig. 3.6b) to distinguish fractures produced by

regional stresses and those related to folding.

Our fracture analysis workflow for the 3D volume (Fig. 3.7) began with applying the

structural smoothing attribute followed by the variance attribute to pre-condition the ant

tracking input. For edge detection (fracture detection), we use the ant tracking algorithm to

map fractures dipping over 75° for the whole 3D volume, for the hanging wall volume, and

for the footwall volume.

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Figure. 3.6. 3D seismic data, a) Show raw data before filtering and cropping. The cross-

section is inline 147 beside the Parrando-1st.1 well, and the location appears as a yellow

line in time slice on the right side of the section. b) show the unwanted cropping data,

separated the 3D volume into the hanging wall, and footwall from Xline 388.

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Figure. 3.7. Fracture analysis workflow. The 3D volume is Input data for Structural smooth

attribute and the output volume is input for next attribute until we get the Ant tracking

attributes volume.

3.4.2. SEISMIC ATTRIBUTE

Seismic attributes consist of physical attributes and geometric attributes. The geometric

attributes represent the characteristics or shape of seismic reflectors such as dip and

azimuth. Physical attributes relate to the lithologic characteristics of the subsurface such as

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amplitude and frequency (Babangida et al., 2013). Research by Hakami et al. (2004),

Chopra and Marfurt (2007), and Backé et al. (2011) has demonstrated that the 3D attribute

is the most useful geophysical technique to characterize faults and fractures. We tested a

number of seismic attributes, including structural smoothing, chaos, variance, and ant-

tracking for fault and fracture detection. For this seismic volume, we found ant-tracking

the most successful attribute for fracture mapping.

3.4.2.1. STRUCTURAL SMOOTHING ATTRIBUTE

In Petrel software, structural smoothing is a tool applied to reduce background noise

and sharpen discontinuities in the seismic horizon and enhance edges (faults) during the

smoothing operation. This attribute helps to remove background noise and increase the

signal to noise ratio for structural interpretation. Figure 8 shows a profile of the raw data

volume before and after generating a new structural smoothing seismic volume.

3.4.2.2. VARIANCE ATTRIBUTE

The variance attribute is an edge-method used to highlight discontinuities in seismic

data, such as faulting and stratigraphic unconformities. Variance measures the similarity in

seismic sample intervals or adjacent traces in vertical or horizontal seismic profiles (Pigott

et al., 2013). Higher variance values represent discontinuity surfaces related to faulting,

channels, unconformities, or sequence boundaries (Pereira, 2009; Pigott et al., 2013). We

test both chaos and variance attributes to see which detects faults and fractures best (Fig.

3.9). Since the variance attributes appear to delineate faults and fractures better than the

chaos attributes, we used variance to pre-condition the seismic volume for ant-tracking.

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3.4.2.3. ANT TRACKING ATTRIBUTE

Ant tracking is a patent-protected Petrel method that uses edge enhancements to look

for sharp discontinuities. Recently, several studies have used ant methodologies to detect

fractures networks. The idea of this method is to follow the analogy of ant behavior using

pheromones for communication to choose the shortest path between nest and food (Randen

et al., 2001; Fehmers and Hocker, 2003; Skov et al., 2003; Pereira, 2009). Variance

attributes were used as input data for the ant tracking. Then we varied the parameters to

get the best fracture image for the Parrando seismic volume. The ant tracking parameters

that we adjusted were: Ant mode: passive, initial ant boundary: 7, ant track deviation: 2,

ant step size: 3, illegal steps allowed: 1, legal steps required: 3, and stop criteria (%): 5.

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Figure. 3.8. Pre-condition process. a) the raw data Inline 147 before applied any filter. b)

Inline 147, after using the structural smoothing attribute.

Figure. 3.9. Pre-condition process for time slice -2549ms. a) Chaos, and b) Variance

attributes to test which one gives us a better image to use it as input for ant tracking. The

Variance shows a good and clear vision for fault and fractures better than Chaos attribute.

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3.4.3. FRACTURE EXTRACTION

The final step is to extract surface segments and fault patches from the ant track

attribute volume (Abul Khair, 2012). Fracture ant tracking was applied to the seismic

volume with the fracture strike azimuths open for all directions (360º) and the fractures

limited to those with dip angles over 75º. Then we applied the second derivative (second

run) from the first ant tracking volume to enhance the fractures. Figure 3.11 shows fault

and fracture patch extraction from the resulting ant track volume with a time slice at 2891

msec. The fracture time slice (Fig. 3.10a) shows that the NE-SW fracture trend azimuth is

dominant. Fig. 3.10b shows the same fracture ant tracking time slice, but with the primary

northeast-southwest fracture trend filtered to highlight secondary fracture orientations. The

fracture extraction process provides significant information about fracture orientation, dip

angle, dip azimuth, intensity, and percentage which can be displayed in stereonets and

histograms.

We then repeated the fault patch extraction on the separate folded hanging wall and

non-folded footwall volumes. To visualize fracture formation and changing stress fields

through time, we extracted time slices at 400 msec intervals from 3351 msec (Late

Cretaceous Une/Gatcheta Formation) to 1351 msec (Pliocene Guayabo Formation).

Finally, we used interactive interpretation "surface extraction" of larger fault patches from

the ant track volume for deterministic fault modeling.

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Figure. 3.10. Ant tracking result in time slice -2891ms. a) show all fracture orientation in

360. b) omitting the primary trend NE-SW. The step is important to present other

orientations clearly when did the fracture interpretation.

Figure. 3.11. Fault and fracture extraction from the ant tracks volume in the right. The

left side presented the ant tracking time slice -2891ms and displayed the fracture set.

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3.5. PARRANDO AND CHAPARRAL FAULT SYSTEMS

3.5.1. FAULT SYSTEM

Figure 3.12 shows a 3D view of the main faults and fractures that we mapped in the

Parrando study area. The faults all have NE-SW trends parallel to the main structural trend

of the Foothills. The Parrando anticline (Fig. 3.5) is a gentle fault-bend fold (200m relief)

with a small break through fault in the forelimb (Hafiz et al., 2019). The structure was

produced by 1.2 km of total shortening. Conformable folding of the Guayabo Formation

above the Leon Formation indicates that the Parrando anticline is very young, and probably

formed in the last 3 Myr (Hafiz et al., 2019). A separate smaller fault-bend fold also

deformed the Mirador reservoir rocks in the footwall. A seismic profile and ant tracking

time slice (Fig. 3.13a) shows Parrando thrust fault hanging wall fractures and breakthrough

fault. The Chaparral fault to the south (Fig. 3.1, 3.13b, d) is also a gentle fault-bend fold

with a small breakthrough fault in the forelimb. Several high angle normal or transtensional

faults are located in the footwall beneath the Chaparral fault (Fig. 3.13b). Faults numbers

3, 2, and 9 also show high angle normal or transtensional faults located in the footwall of

the Parrando thrust fault (Fig 3.13 c). The normal and strike slip displacements appear to

be very young (late Miocene-Pliocene).

3.5.2. PARRANDO FRACTURE SYSTEMS

Figure 3.14 shows the ant-tracking results for fractures dipping over 75 degrees

showing fracture rose diagrams, dip azimuth histograms; and ant-tracking time slices for

a) the whole 3D volume, b) the Parrando thrust fault hanging wall and c) the Parrando

footwall. We found two prominent fracture systems, NE-SW and NW-SE. The major

fracture strike azimuth for the whole seismic volume (Fig. 3.14a) is northeast-southwest

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Figure. 3.12. Faults modeling for Parrando anticline.

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Figure. 3.13. Parrando thrust fault. a. seismic inline 194 and 2177 msec ant tracking time

slice shows NE- SW Parrando thrust hanging wall fractures and breakthrough fault. b.

Seismic inline 404 and 2855 msec time slice show the NE-SW Chaparral lower fault and

footwall fractures. c. Inline 210 and 3291 msec time slice show NE-SW and N-S fracture

sets in the Parrando footwall. d. Inline 439 and 2233 msec time slice show NE-SW fracture

sets in the Chaparral hanging wall. Small ant-tracking maps show the profile locations.

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(040 ± 15°) parallel to the structural trend of the Foothills. The corresponding dip azimuths

are 130 ± 10° and 310 ± 10°, making up about 28% of the total fracture dip azimuths. We

can see in the ant-tracking time slices that the NE-SW trend is prominent at all depths in

the post-rift sediments from 1350 to 3350 msec, and it is especially concentrated in the

folded rocks of the Parrando and Chaparral anticlines (Fig. 3.14a).

The secondary fracture strike azimuth (Fig. 3.14b) is northwest-southeast (135 ± 10°)

perpendicular to the structural trend of the Foothills. The corresponding dip azimuths 050

± 10° and 230 ± 10° make up about 18% of the total dip azimuths. The NW-SE fracture

trend is particularly strong in the non-folded footwall rocks. It is found at all depths in the

post-rift section, but it is especially pronounced at 2100-2600 msec (Fig. 3.14c) in the upper

Miocene age footwall rocks of the Carbonera Group.

3.5.3. FOLDED HANGING WALL FRACTURE SYSTEMS

We divided the seismic volume into a northwestern folded segment on the Parrando

and Chaparral thrust fault hanging wall blocks and a non-folded volume in the footwall

block to the southeast. In this way, we hoped to distinguish fold related fractures from those

produced by other regional stresses. In the folded hanging wall (Fig. 3.14b) ant tracking

rose diagrams for fractures dipping over 75 degrees show a dominant NE-SW (040 ± 15º)

fracture strike azimuth trend parallel to the primary structural trend in the Foothills. The

corresponding dip azimuths (130 ± 10º; 310 ± 10º) are 38% of the total dip azimuths (Fig.

3.14b). The northeast-southwest set is observed in all stratigraphic units from Une to

Guayabo formations. A much less prominent fracture set in the folded hanging wall is

oriented NW-SE (135 ± 10º) perpendicular to the regional structural strike (Fig. 3.14b).

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The dip azimuths for the NW-SE fracture set (050 ± 10º; 230 ± 10º) make up only 10% of

the total hanging wall fractures (Fig. 3.14b) and are only observed in the youngest Miocene

age Leon and Guayabo formations. Ant-tracking time slices and seismic profiles (Figs.

3.13 a and d) show NE-SW fractures and faults in the folded hanging wall with small

reverse displacements.

3.5.4. NON-FOLDED FOOTWALL FRACTURE SYSTEMS

In the non-folded footwall (Fig. 3.14c) ant-tracking rose diagram for fractures dipping

over 75 degrees shows more diverse orientations than the hanging wall, including NE-SW

and NW-SE azimuths. Like the folded hanging wall, the dominant fracture trend in the

footwall is NE-SW (040 ± 15º) parallel to the structural trend of the Foothills. However,

the NE-SW trend is not as pronounced in the footwall as in the folded units above the

Parrando thrust. The corresponding fracture dip azimuths (130 ± 10º; 310 ± 10º) only make

up about 21% of the total fractures in the footwall (Fig. 3.14c). Ant-tracking time slices

and seismic profiles in Figs. 3.13b, 3.13c, and 3.16d show high angle NE-SW fracture sets

with minor transtensional down to the SE displacement in the footwall. The NW-SE trend

(140 ± 10º) is more prominent in the footwall than in the folded hanging wall, and the

associated fracture dip azimuths (050 ± 10º; 230 ± 10º) for the NW-SE trend make up 17%

of the total dip azimuths in the footwall. Thus, the fractures in the footwall are more

bimodal than in the folded hanging wall. As noted above, the NW-SE fracture trend is

found at all depths in the post-rift section, but it is especially pronounced at 2100-2600

msec (Fig. 3.14c) in the upper Miocene age footwall rocks of the Carbonera Group. An

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ant-tracking time slice and seismic profile (Fig. 3.16b) also shows an uncommon north-

south fracture trend in the non-folded footwall.

By examining the ant-tracking footwall volume throughout the post-rift sedimentary

section in time slices (Fig. 3.14c) and in horizon slices (Fig. 3.15) we can see changes in

the fracture set orientations through time and indirectly clues to changing regional stress

fields from the Late Cretaceous to Present. For example, in the 3351 msec time slice (Upper

Cretaceous 100-85 Ma Gatcheta Fm) we observe NE-SW and N-S oriented fracture sets

(Figs. 3.14c and 3.15f). In the 2951 msec time slice and Fig. 3.15d (Oligocene Carbonera

Fm 36-28 Ma C8-C7), we observe very prominent NE-SW fracture sets. In the 2551 msec

time slice (Miocene Carbonera Fm 21-18 Ma C3- C2) NW-SE and N-S fracture set

orientations can be seen. Up section in the 2151 msec time slice (Miocene early Leon Fm

3.14 Ma) the NW-SE fracture set has become very prominent. Higher in the seismic

volume in the 1751 msec time slice and Fig. 3.15a (Miocene late Leon Fm 9 Ma) the NW-

SE azimuth fracture sets continue to be predominant (Fig. 3.14c). Finally, up section in the

1351 msec time slice (Pliocene Guayabo Fm 6 Ma) we observe both NW-SE and NE-SW

oriented fracture sets.

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Figure .3.14. Ant-tracking fracture rose diagrams for fractures and histogram dipping over

75 degrees, showing strike azimuths (rose petals), dip azimuths (points); dip azimuth

histograms; and ant-tracking time slices for: a) whole 3D volume b) Parrando hanging wall

and c) Parrando footwall.

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Figure. 3.15. Horizon ant-tracking fracture networks: a) Leon Fm, b) Carbonera C1 Fm, c)

Carbonera C5 Fm, d) Carbonera C7 Fm, e) Mirador Fm, f) Gacheta Fm.

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Figure. 3.16. Ant-tracking time slices and seismic profiles show a) E-W fracture in the

footwall. b) N-S fractures in the hanging wall, c) NW-SE fracture sets in the footwall, and

d) NE-SW fracture sets in the footwall.

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3.6. DISCUSSION

Previous studies of fractures in the Foothills of the Eastern Cordillera have

generally relied on surface geologic studies or downhole imager logs (e.g., Egbue et al.,

2014; Tamara et al., 2015). Albesher et al. (2020) used multi-attribute analysis of a 3D

seismic volume in the Foothills (La Florida anticline) using coherency and ant-tracking

techniques for fault and fracture detection. Cazier et al. (1995) found the Eocene Mirador

Fm (the main reservoir) has low porosity but good permeability in the giant Cusiana oilfield

northeast of Parrando anticline. Well tests indicated that the type of permeability was

primarily matrix related (Cazier et al., 1995), however, fluid flow was likely also

influenced by augmented fracture permeability (Matthäi and Belayneh, 2004).

Using borehole breakouts and seismic focal mechanisms Egbue et al. (2014) found

two present-day principal stress directions in the Eastern Cordillera; WNW-ESE to NW-

SE, aligned with the GPS measured Panama-North Andes collision, and E-W to WSW-

ENE, aligned with the northeastward “escape” of the North Andes. The dominant NW-SE

fracture systems observed in the Cupiagua fold structures on the eastern flank of the

Eastern Cordillera are produced by range-normal compression and range parallel extension

(Egbue et al., 2014). Less well developed asymmetrical shear fractures oriented E-W to

WSW-ENE and NNW-SSE may be related to prefolding stresses in the foreland basin of

the Central Cordillera (future Eastern Cordillera) or to present-day shear associated with

the northeastward “escape” of the north Andean block (Egbue et al., 2014). Tamara et al.

(2015) found four fracture sets in the Foothills folded reservoir rocks from surface mapping

and well data: NE-SW, NW-SE, E-W, and N-S, and related their distribution to fold

geometry and folding mechanism.

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3.7. CONCLUSION

In this study we used attribute analysis and ant-tracking algorithms on a 3D seismic

volume to map subsurface fracture system orientations and intensities. We then use the

fracture patterns to predict relative ages and directions of regional stresses. We found two

prominent fracture systems, NE-SW and NW-SE. The major fracture strike azimuth for the

whole seismic volume is northeast-southwest (040 ± 15°) parallel to the structural trend of

the Foothills. The corresponding dip azimuths are 28% of the total fracture dip azimuths.

The NE-SW trend is especially concentrated in the folded rocks of the Parrando and

Chaparral anticlines. Several NE-SW fractures show minor extensional displacement

consistent with folding in the hanging wall or an elastic plate subjected to pure bending in

the footwall.

The secondary fracture strike azimuth is northwest-southeast (135 ± 10°)

perpendicular to the structural trend of the Foothills. The corresponding dip azimuths make

up 18% of the total dip azimuths. The NW-SE fractures are Type 1 fracture sets resulting

from a vertical intermediate stress and maximum compressive stress parallel to the dip

direction of bedding. Set 1 fractures form early during folding with the regional maximum

compressive stress normal to the advancing mountain front. In the tightly folded Cupiagua

field, a NW-SE trending fracture set is also widespread. The NW-SE fracture trend is

particularly strong in the mid Miocene age Parrando footwall rocks of the Carbonera

Group.

By examining the ant-tracking footwall volume throughout the post-rift

sedimentary section we can see changes in the fracture set orientations through time and

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infer changing regional stress fields from the Late Cretaceous to Present. NE-SW fractures

in the Late Cretaceous Gatcheta Fm (100-85 Ma) source rocks may have been inherited

from rift related normal faulting. NE-SW fractures in the Oligocene (36-28 Ma) Carbonera

Fm C8-C7 may have been early folding or bending of the lithosphere before the advancing

mountain front.

NW-SE fractures are found from the Miocene (21 Ma) Carbonera Fm C3-C2, and

Leon Fm, to the Pliocene Guayabo Fm (6 Ma). The NW-SE fracture trend is most

prominent in the mid-Miocene at about 14 Ma. Since these strata pre-date the 6-3 Ma

Andean folding of the Parrando anticline, the NW-SE fracture set may be inherited from

the earlier initial folding and thrusting in the nearby Guavio anticline and Guaicaramo

thrust fault.

This study demonstrated the utility of attribute analysis and ant-tracking technology

for detecting fractures and faults in 3D seismic volumes where subsurface borehole

imagery is not available. Application of this coherence and ant-tracking methodology in

foreland structures, such as Cusiana, would help to validate the method and visualize

fracture patterns between wells and potentially improve predictions of reservoir fracture

porosity, permeability, and fluid pathway.

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CHAPTER IV

POTENTIAL APPLICATIONS FOR 3D SEISMIC ATTRIBUTE

FRACTURE ANALYSIS

The previous chapter demonstrated the utility of attribute analysis and ant-tracking

technology for detecting fractures and faults in 3D seismic volumes where subsurface

borehole imagery is not available. Fractures are discontinuities in a rock that can either

contribute to fluid flow or act as barriers. This makes understanding the fracture network

within a fractured reservoir essential for the enhancement of hydrocarbon production as

well as any study that requires knowledge of fluid flow, permeability, and porosity. The

application of coherence and ant-tracking techniques for fracture analysis is not novel,

although publications presenting case studies are limited (e.g., Fehmers and Hocker, 2003;

Pereira, 2009; Khair et al., 2012; Schneider et al., 2016). The last chapter presented,

together with Albesher et al. (2020) the first applications of these methods in the Eastern

Cordillera of Colombia and one of the first case studies in an actively deforming foreland

basin. This chapter briefly discusses other potential applications of attribute analysis for

fracture modeling, including predicting the evolution of regional stresses with time,

reservoir stimulation, CO2 sequestration, hydrogeology, and mineral exploration.

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4.1. EVOLUTION OF REGIONAL STRESS FIELDS

As discussed in the preceding chapter, stress regimes can strongly affect the

permeability of ancient fractures that formed in a different, older stress regime. The

propagation paths for fractures in a geologic setting are strongly influenced by the state of

stress and are only weakly dependent on the rock fabric (Olson and Pollard, 1989). Vertical

fractures propagate normal to the least principal stress, thus, they follow the path of the

stress field present at the time of their propagation (Engelder and Geiser, 1980). By

examining a map of fracture-set orientation, we can infer the differential stress that was

active during their propagation.

By examining the ant-tracking volume throughout the sedimentary section in the

Foothills of the Eastern Cordillera of Colombia (Hafiz et al., 2020, chapter 3), changes in

the fracture set orientations were apparent with time, revealing changing regional stress

fields from the Late Cretaceous to Present. NE-SW fractures in the Late Cretaceous (100-

85 Ma) rocks may have been inherited from rift related normal faulting. NE-SW fractures

in the Oligocene (36-28 Ma) may have been early folding or bending of the lithosphere

before the advancing mountain front. NW-SE fractures were found from the Miocene (21

Ma) to the Pliocene (6 Ma), and were most prominent in the mid-Miocene at about 14 Ma.

The orientation may have indicated the initiation of thrusting in the Foothills with a NW-

SE oriented maximum compressive stress direction (Stearns, 1968). The Panama arc-North

Andes collision also began about 15-12 myrs ago (Egbue et al., 2014; Kellogg et al., 2019).

Egbue et al. (2014) also observed these dominant NW-SE fracture systems northeast in the

Foothills and assigned them to range-normal compression and range parallel extension.

Thus, where high quality 3D seismic data is available and deformation is moderate, the

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coherence attribute and ant-tracking method can be a powerful tool for measuring changes

in fracture orientation and intensity throughout the 3D volume and hence indirectly

revealing changes in regional stress fields with time.

4.2. RESERVOIR STIMULATION, GEOTHERMAL, CO2 SEQUESTRATION,

PASSIVE SEISMIC

Until now, the principal applications of coherence attribute analysis for fracture

mapping have been directed at reservoir fluid flow analysis and permeability modeling for

hydrocarbon production. For example, Schneider et al. (2016) developed a discrete fracture

network modeling technique based on poststack seismic attribute calculations to

characterize the fracture network of the Tensleep Formation at Teapot Dome in Wyoming,

USA. The used poststack seismic attributes were coherence, curvature, coherence on

spectral decomposed seismic cubes, and textural attributes based on the gray-level co-

occurrence matrix (GLCM). In the south dome of the Abqaiq field in Saudi Arabia, seismic

attributes are being used to characterize small‐scale faults and reduce reservoir drilling risk

(Lawrence, 1998). Khair et al. (2012) noted that the future success of both enhanced

(engineered) geothermal systems and shale gas production will rely significantly on the

development of reservoir stimulation strategies that suit the local stress and mechanical

conditions of the prospects. The orientation and nature of the in-situ stress field and pre-

existing natural fracture networks in the reservoir are amongst the critical parameters

controlling the success of any stimulation program.

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Seismic attribute “ant tracking” is also being use to reduce the risk of drilling for

suitable reservoirs for CO₂ sequestration. For example, in Algeria’s In Salah carbon dioxide

storage project, many post-stack seismic attributes were calculated from the 3D seismic

data, including positive and negative curvatures as well as ant tracking. The maximum

positive curvature attributes and ant tracking found the clearest linear features, with two

parallel trends, which agreed well with the ant-track volume and the InSAR observations

of a depression zone (Zhang, 2015).

Fracture seismic is another seismic method for mapping fractures in the subsurface

by recording and analyzing passive seismic data (Sicking and Malin, 2019). Fracture

seismic is able to map the fractures because of two types of mechanical actions in the

fractures. First, in cohesive rock, fractures can emit short duration energy pulses when

growing at their tips through opening and shearing. The industrial practice of recording

and analyzing these short duration events is commonly called micro-seismic. Second,

coupled rock–fracture–fluid interactions take place during earth deformations and this

generates signals unique to the fracture’s physical characteristics. This signal appears as

harmonic resonance of the entire, fluid-filled fracture. These signals can be initiated by

both external and internal changes in local pressure, e.g., a passing seismic wave, tectonic

deformations, and injection during a hydraulic well treatment (Sicking and Malin, 2019).

Fracture seismic is used to map the location, spatial extent, and physical characteristics of

fractures. The strongest fracture seismic signals come from connected fluid-pathways.

Fracture seismic observations recorded before, during, and after hydraulic stimulations

show that such treatments primarily open pre-existing fractures and weak zones in the

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rocks. Time-lapse fracture seismic methods map the flow of fluids in the rocks and reveal

how the reservoir connectivity changes over time.

4.3. HYDROLOGY

Lei et al. (2017) stressed the importance of the presence of natural fractures, which

can result in heterogeneous stress fields and channelized fluid flow pathways, However,

direct observation of the detailed 3D structure of fracture networks deep in the crust is

impossible. Field data are usually collected from limited exposures, e.g., one-dimensional

(1D) borehole logging and two-dimensional (2D) outcrop mapping. Seismological surveys

may be able to locate 3D large-scale structures, but the current technology can hardly detect

widely-spreading medium and small fractures due to the resolution limit (Lei et al., 2017).

It is challenging to visualize water underground. Groundwater fully saturates in pores or

cracks in soils and rocks. Hustoft et al. (2009) integrated 3-D seismic observations with

two- dimensional (2-D) sedimentation measurements to model fluid flow and quantify the

effects of sediment loading and erosion on overpressure generation and fluid expulsion.

The models simulate the temporal evolution of compaction-driven overpressure and fluid

expulsion based on sedimentation rates estimated from seismic data and hydrologic and

sediment properties obtained from laboratory experiments and petrophysical data. Lei et

al. (2017) used discrete fracture networks (DFN) to model coupled geomechanical and

hydrological behavior for subsurface rocks with data from 3D seismic, borehole logging,

and 2D surface mapping.

Mallants et al. (2018) developed methods to improve risk assessments associated with

deep groundwater extraction and depressurisation from energy resource development (coal

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seam gas extraction in Australia). The goal was to improve the predictive capability of

regional groundwater flow models with respect to the representation of faults and aquitards.

In a case study evidence for near-surface expressions of geological faults (i.e. in the top 50

to 100 m) was derived from a shallow Time domain Electromagnetic (TEM) survey.

Inference of fault traces from the combination of near-surface geophysics and deeper

seismic analysis, together with evidence from tracer analysis indicated the presence of both

slow moving groundwater (i.e. diffusion-driven mass transport) and faster moving

groundwater (i.e. advection-driven mass transport). The former was inferred from one

dimensional modelling of methane and helium profiles, while evidence of the latter was

found in tracer hotspots.

However, while hydrologists recognize the importance of understanding the detailed

3D structure of fracture networks for predicting fluid flow pathways and creating

groundwater flow models, no publication was found documenting use of the latest spectral

decomposition and ant tracking techniques to study fractures in aquifers. A promising

opportunity therefore exists to apply coherence attribute fracture analysis of 3D seismic

data to water and pollutant flow models.

4.4. MINERAL EXPLORATION

Geophysical methods are commonly used in the early stages of mineral exploration,

including gravity, magnetic, radiometric, electrical current, resistivity, induced polarity,

electromagnetic, and radioactivity methods. Seismic reflection and refraction methods

have become more common for mineral exploration in recent years. In South Africa,

Duweke et al. (2002) used high resolution seismic data to map three dimensional geological

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structures and assess the size, geometry and distribution of mineable blocks, information

that was incorporated throughout the mine development and production phases. Mining

environments are often characterized by intensely fractured, faulted, and folded geology

that can result in steeply dipping laterally discontinuous and heterogeneous host rock units.

Naghizadeh et al. (2019) in the Metal Earth project-Canada, used seismic methods and

seismic attributes at the crust-mantle scale to identify key geological-geochemical-

geophysical attributes of metal sources, transport pathways, and economic concentrations

at the crust–mantle scale. Cichostępski et al. (2019) used prestack seismic data to evaluate

the sulfur content within a carbonate reservoir. They imaged the sulfur bearing strata with

a simultaneous inversion procedure to recover porosity changes and sulfur content, and

demonstrated that the sulfur content was dependent on the carbonate reservoir’s porosity.

Bellefleur and Adam (2019) used 3D seismic datasets for mineral exploration and

demonstrated improved imaging of mineralized bodies in three mining areas using

processing flows tailored to enhance the seismic data. Now 3D seismic surveying is used

for routine mine planning and development purposes. First, the seismic survey can

illuminate major structural features, such as faults or folds that control mineral location.

Then 3D seismic data may reveal rock elastic seismic responses related to petrophysical

properties associated with mineral ore deposits.

However, as in hydrology, despite the common use of 3D seismic data for mine

planning and development and the importance of fractures in mineral ore deposits, no

published applications of modern coherence attribute and ant-tracking fracture analysis

89

could be found. This may then be another opportunity to apply seismic attribute analysis

to a new field, mining exploration.

4.5. FUTURE WORK

Exploration in the Eastern Cordillera Foothills of Colombia has focused on Eocene

Mirador Formation reservoir rocks. However, the presence of hydrocarbons in C5 in

Parrando-1 well confirms the presence of an active hydrocarbon system and suggests the

potential for Oligocene Carbonera Formation oil accumulations in Parrando and elsewhere

in the Foothills.

The study in chapter 3 demonstrated the utility of attribute analysis and ant-tracking

technology for detecting fractures and faults in 3D seismic volumes where subsurface

borehole imagery is not available. Application of this coherence and ant-tracking

methodology in a foreland structure, such as the giant Cusiana anticline oil field in the

Foothills of the Eastern Cordillera of Colombia, where abundant downhole data is

available, would serve two purposes. First, it could validate the method by comparing the

predicted fracture intensity and orientation patterns from seismic attribute analysis with

direct downhole observations of fractures. Second, it would enable visualizion of fracture

patterns in three dimenstions between wells, including fracture porosity, permeability, and

fluid pathways and improve production modeling. Fracture orientations and permeability

in Cusiana have been well documented by Cazier et al. (1995) and Tamara et al. (2015) for

comprehensive downhole well datasets.

Potential applications of attribute analysis for fracture modeling include predicting the

evolution of regional stresses with time, reservoir stimulation, CO2 sequestration,

90

hydrogeology, and mineral exploration. A promising opportunity exists to apply coherence

attribute fracture analysis of 3D seismic data to water and pollutant flow models.

Considering the common use of 3D seismic data for mine planning and development and

the importance of fractures in mineral ore deposits, modern coherence attribute and ant-

tracking fracture analysis may have application in mineral exploration.

91

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