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Interdisciplinary Study of Reservoir Compartments Contract No. DE-AC22-93BC14891

Document Control Center U.S. Department of Energy Pittsburgh Energy Technology Center

Pittsburgh, PA 15236-0940 P.O. BOX 10940, MS 921-1 18

Contract Specialist: Mary Beth J. Pearse

Craig W. Van Kirk Principal Investigator Robert S. Thompson Project Manager Petroleum Engineering Department Colorado School of Mines Golden, Colorado 80401

July21, 1995

Quarterly Technical Progress Report

Disclaimer

' T h i s report was prepared as an account of work sponsored by the United States Government. Neither the United States, any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liabilities or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infkinge privately owned rights. Reference herein to any specific commercial product, process, or service, by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof"

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"USDOE Patent clearance is not required prior to the publication of this document."

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DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

INTERDISCIPLINARY STUDY OF RESERVOIR COMPARTMENTS AND HETEROGENEITY

Contract No. DE-AC22-93BC14891

Colorado School of Mines Golden, CO

Date of Report: July 20,1995 Contract Date: September 29,1993 Anticipated Completion: Sept. 30,1996 Government Award: $753,266

Principal Investigator: Craig W. Van Kirk

Project Manager: Robert S. Thompson

Reporting Period: April 1-June 30,1995

Objectives

This United States Department of Energy (DOE) research project was established to document the integrated team approach for solving reservoir engineering problems. A field study integrating the disciplines of geology, geophysics, and petroleum engineering will be the mechanism for documenting the integrated approach. This is an area of keen interest to the oil and gas industry. The goal will be to provide tools and approaches that can be used to detect reservoir compartments, reach a better reserve estimate, and improve profits early in the life of a field.

Summary of Technical Progress

Reservoir Characterization

In previous reports, the petrophysical analysis, core descriptions, and minipermeameter results were integrated to develop a correlation to estimate permeability from log derived data.

During this quarter, the production data was integrated into the analysis. The result is an approach that improves volumetric reserves estimates.

The incorporation of the minipermeameter work resulted in the use of moved hydrocarbons to discriminate pay. Moved hydrocarbon is estimated from the difference between BVW and BVZ. BVW is the bulk volume water (water saturation times the porosity) calculated for the uninvaded zone. BVZ is the bulk volume water for the mixed zone near the wellbore. The water in this zone is considered to be a mixture of the formation water and the water from the drilling fluid.

The production data was analyzed using an Infinite Conductivity Fracture Production Type Curve.’ Estimates of drainage area, fracture length, and permeability were made from the type curve match using estimates for net pay and porosity from log derived data. When the resulting fracture lengths and drainage areas were plotted to scale at individual well locations to visually check the drainage patterns across the reservoir, refinements in the petrophysical analysis were warranted. An iterative procedure was used to adjust the log derived values for net pay to better reflect the production performance. The integration of the production data shows that the traditional type of cutoffs (porosity, water saturation, and shale volume) were pessimistic when compared to the ultimate recoveries and reasonable recovery efficiencies. The initial cuttoff values and the cuttoffs that roughly coincide with the BVW-BVZ technique are summarized in Table 1.

TABLE 1 Comparison of Petrophysical Cutoff Values

Initial Volumetric Calculations and Revised Values After Production Data Analysis

Parameter Initial (%) Revised(%) Porosity 3 8

Water Saturation 55 65 Shale Volume 40 45

.

Documentation of the BVW-BVZ Pay Discrimination Technique

When using Induction logs the invasion profile can be conksing. In a productive hydrocarbon bearing zone the profile would be (from low to high resistivity) Deep, Medium, and then the Shallow (SFL) tool. This is just opposite to the response that a Lateralog would have. What this means is that the shallow tools almost always read a higher resistivity than the deep investigation tools in the pay zone. For illustration, Archie’s law is applied ignoring shale volume corrections.

True Formation

s, = &l:x: n

Flushed Zone

Mixed Water

flushed zone fiom truly being flushed of all of the original formation water.

Useklness of the BVW-BVZ technique

1) Helpful to discriminate pay

2) Correlates very well to the minipermeameter measurements

Although we have found the method to be useful in the discrimination of pay zones, the amount of the flushing and how it relates to permeability may not be a good consistent inference tool. This is because the quality of the digital data can make a big difference in the results of the inferred permeability.

Reservoir Simulation

Isopach maps have been generated for the four marine parasequences. The maps validate the geologic interpretation and correlation scheme. The maps will be incorporated into the reservoir simulation. Geologic and geophysical fault interpretations have been digitized and incorporated into the reservoir simulator. Field wide simplistic simulations have also been tested.

The z denotes a mixed water zone. To calculate the moved hydrocarbons due to invasion, typically BVW is compared to BVXO (bulk volume for the flushed zone). In the case of induction logs this will always indicate that there is pay everywhere due to the nature of the contrast in water resistivities. When the mixing of the fresh mud filtrate with the saline formation water is considered, there will be an indication of flushed hydrocarbons. The mixing scenario is a more realistic model than the flushed zone model since the clays will still have a relatively high concentration of formation water that is trapped in their matrix and on their surfaces. The very low permeability of the formation also keeps the

Based on gas-oil ratios and production trends, it was concluded that the fluids were distributed in two main areas: a predominantly oil area and a predominantly gas area. These main areas are separated along a diagonal south- west to north-east trend, as shown in Fig. 1. Evidence reported previously indicates the faults are sealing. For the vertical fluid distribution, integration of the production behavior with structural cross sections and completions is in progress an will provide a more accurate distribution of the fluids in the reservoir before exploitation started in the area.

Outcrop Analog

The Upper Cretaceous Mesaverde Group was selected as an outcrop analog for the Terry

Sandstone reservoir at the Hambert-Aristocrat Field. The Mesaverde outcrop affords the opportunity to observe both the style of offset faulting which has compartmentalized the Terry Sandstone and the long-distance stratigraphic continuity of the sandstone (when not offset by faults). The field work is in progress and the results will be incorporated into the final reservoir description.

References

1. Cox, Dave O., Infinite Conductivity Fracture Production Type Curve, Unpublished work used with permission, 1995.

66W 65W

LEGEND GOR < 5 Mscf/bbl

Q

GOR < 10 HsCf/bDJ

e GOR < 50 MSCF/DDI -- GOR > SO mscf/btil

13

25

36

1 ,

'6 i " i +

Fig. 1 Terry Structural Tops and GOR Map.