tom wilson department of geology and geography west virginia university morgantown, wv

TOM WILSONDEPARTMENT OF GEOLOGY AND

GEOGRAPHYWEST VIRGINIA UNIVERSITY

MORGANTOWN, WV

Developing a strategy for CO2 EOR in an unconventional reservoir using 3D seismic attribute

workflows and fracture image logs

Tom Wilson, Department of Geology and Geography

ACTIVITY & ELEMENT 2.651.070.001.511

FAULT AND FRACTURE ZONE DETECTION AND REDUCED ORDER FRACTURE MODEL

DEVELOPMENT FOR RISK ASSESSMENT

Overview


1) Reservoir characterization is developed using analysis of 3D seismic and fracture image logs and seismic attribute workflows for fracture driver development to distribute fracture intensity throughout the reservoir.

2) Analysis of fracture image logs reveals that the dominant open fracture trend within the reservoir is coincident with present-day SHmax.

3) Outcrop analogs and satellite observations are used to develop model distributions of fracture length, height and spacing

4) Fracture intensity driver is developed using a combination of seismic discontinuities and directional curvature (orthogonal to SHmax).

5) Reservoir compartmentalization is interpreted.

6) A strategy for CO2 EOR is proposed that incorporates placement of injection and production laterals along compartment boundaries and roughly orthogonal to SHmax.

Location of study area and reservoir structure


Dip line views of structure


Basement

MadisonTensleep

Goose Egg

AlcovaMorrison

Wall Creeks


Fracture characterization using image logs. Open fractures in seal, reservoir and in total

SHmax

Open fracture trends in the reservoir by well and for all wells


SHmax

280’Fracture ZoneFracture Zone

Field analogs of seismic discontinuities

Defining fracture parameters-Fracture height distribution


Length (m)

1 10 100

Num

ber

1

10

100

Fracture Height (m) High Intensity Zone (right)

power = -1.62

R2=0.96

Heights >2m

Length (m)1 10

Num

ber

1

10

100

Fracture Height (m) High Intensity Zone (left)

power = -1.61

R2=0.96

Heights >2m

Length (m)

1 10

Num

ber

1

10

100

Fracture Height (m) Middle Low Intensity Zone

power = -2.18

R2=0.86

Heights >2m

Higher power implies lower probability of higher fractures


-1.61 -2.18 -1.62

Spacing distributions estimated in Freemont Canyon


Spacing (meters)10

Num

ber

1

10

100HI Fracture Zone 3

power = -1.28

R2=0.98

power = -2.8

R2=0.97

power = -0.47

R2=0.95

Spacings (meters)10 100

Num

ber

1

10

100

1000Entire Exposure

power = -0.43

R2=0.95

power = -1.55

R2=0.99

Variations of fracture intensity in the reservoir


Zone

FZ1 IntZ FZ2 IntZ

Inte

nsit

y

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07Fracture intensity by vertical zone

Selected layers (top-to-bottom)

L1 L2 L3 L4 L5 L6 L7 L8 L9 L10

Inte

nsit

y

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08Variations of fracture intensity through the Tensleep

average = 0.042with 95% confidence limits from 0.031 to 0.054

Fracture length distributions from World view ½ meter resolution imagery


Outcrop viewed from opposite side of canyon

Local fractures mapped using WorldView imagery


Fracture length distributions(from WorldView imagery)


Length(m)

10

Num

ber

1

10

100

1000Fracture Length Distribution (L>4m)

power = -1.85

R2=0.98

Seismic discontinuity length distribution


Length (meters)100 1000

Num

ber

1

10

100

1000Discontinuity Lengths

Length (meters)100 1000

Num

ber

10

100

Discontinuity Lengths

power = -2.29

250 < length <650

Aperture distributions – log normal with some power law behavior for apertures above ~0.05 mm


log10 Electrical Aperture-4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

Freq

uenc

y

0

5

10

15

20

25

30

log10 Hydraulic Aperture-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

Freq

uenc

y

0

5

10

15

20

25

30

35

A B

log10 hydraulic aperture-3.0 -2.5 -2.0 -1.5 -1.0 -0.5

log

cum

ulat

ive

num

ber

0.0

0.5

1.0

1.5

2.0

2.5

log10 electrical aperture-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5

log

cum

ulat

ive

num

ber

0.0

0.5

1.0

1.5

2.0

2.5

Slope = -1.72

R2=0.98

-1.3

Slope = -1.73

R2=0.97

-1.25

A. B.

Seismic discontinuity detection workflow


A variety of post-stack processing workflows have been developed as part of this research. Multiple workflows are usually tested and compared. Some example discontinuity detection workflows are shown at left.

Often, discontinuities can be significantly enhanced simply by taking the absolute value of the seismic trace or taking a trace derivative followed by taking it’s absolute value.

Low pass filtering is sometimes required to reduce high-frequency noise.

Discontinuity detection workflow components

Comparison of amplitude and enhanced seismic data


In general, data prep is an iterative process

The derivative enhances high frequency content and introduces a 90o phase shift


Frequency

0 20 40 60 80 100

Am

plitu

de

0.000

0.004

0.008

0.012

0.016

Signal Spectrum

Frequency

0 20 40 60 80 100

Am

plit

ude

0

500

1000

1500

Spectrum of the Derivative

Absolute value doubles apparent spectral content


Frequency

0 50 100 150 200 250

Am

plitu

de0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007Spectrum of Absolute Value of the Derivative

Frequency

0 50 100 150 200 250

Am

plitu

de

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025Spectrum of Absolute value of Signal Amplitude

Extracted discontinuities


NE oriented discontinuities are interpreted to arise from right lateral transpressional shear


S1 Fault

Incorporating possible influence of curvature on dominant fracture aperture


Maximum directional curvature orthogonal to the dominant open fracture set & SHmax.

SHmax

Potential compartmentalization within the reservoir suggested by production distribution


Log 10 yr cumulative production5 yr cumulative production

(Smith, 2008)

Volume probe through combined discontinuity and directional curvature volume


Composite driver development


• Discontinuities and directional curvature were extracted from 3D seismic.

• Conditional statements were used to zero-out high-scoring discontinuities and isolate positive curvature.

• Only regions with positive curvature were incorporated in the intensity driver.

• Discontinuity and curvature parameters were upscaled into a model grid and combined to produce an intensity driver that could be used to control the distribution of fractures in the reservoir.

Intensity distribution


Drilling strategy


CO2 injection

lateral

Production lateral

SHmax

SHmax

Dominant open

fracture trend

injector

producer

Workflow integration


Determine Orientation of Shmax

from Drilling Induced fractures

or Breakouts

Analyze Distributions of Dominant Open Fracture Trends

Examine directional Curvature at Scale

of Seismic Discontinuities

Derived 3D Discontinuity

Volume

Identify potential for compartmentalization

Manipulate Attribute Values to Highlight Low and High Permeability regions in Reservoir

Upscale and Combine to Provide Fracture Intensity

Driver

Incorporate Analysis of Field Data to Help

Constrain Length, Height and Spacing

Distributions

Estimate Aperture Distribution

Develop DFN

Field analogImage log3D seismic

Continued from Discontinuity

Detection Workflow

Novel aspects of the approach


1) The new driver addresses the possibility that NE oriented higher-score discontinuities may represent low permeability zones that could compartmentalize the reservoir; and,

2) use of maximum directional curvature orthogonal to the more prevalent N76oW hinge-oblique open fracture set in the reservoir focuses on that curvature component that could enhance apertures of the dominant fractures set. Curvature in this direction acts in tandem with the orientation of SHmax inferred from induced fractures observed in the fracture image logs to enhance permeability in the N76W trend.

Recent paper and meeting preparations


Developing a strategy for CO2 EOR in an unconventional reservoir using 3D seismic attribute workflows and fracture image logs: Paper submitted for presentation at the Annual SEG meeting, Sept., 2013, Thomas H. Wilson, National Energy Technology Laboratory and West Virginia University; Valerie Smith, Schlumberger Carbon Services, and Alan Brown, Schlumberger NExT, 5p.

Characterization of Tensleep reservoir fracture systems using outcrop analog, fracture image logs and 3D seismic: Abstract submitted for presentation at the Annual AAPG Rocky Mountain Section meeting, Thomas H. Wilson, National Energy Technology Laboratory and West Virginia University; Valerie Smith, Schlumberger Carbon Services, and Alan Brown, Schlumberger NExT

Future work1. carry through to simulation, or


Develop DFN in FRACGEN

Field analog

Image log analysis

Seismic analysis

Devise methods for incorporating results from

seismic analysis into FRACGEN model

Bring in production data

Bring in reservoir parameters (Smith, 2008)

Incorporate in ROM

Simulation and history matching

Reservoir Engineering

Bring in additional field observations: Alcova and Granite Mountain Anticlines

Future work2. carry through to simulation in alternative unconventional reservoir


The reservoir characterization workflows presented here can be extended to other reservoirs as needed to

support NETL priorities.

DFN’s, although not presented as part of today’s discussions, have been developed for numerous

reservoirs. The methodologies are adaptable and can be readily applied to new settings given sufficient data.

tom wilson department of geology and geography west virginia university morgantown, wv

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