. "APPENDIX C: RESERVIOR CHARACTERIZATION." Maintaining Oil Production from Marginal Fields: A Review of the Department of Energy's Reservoir Class Program. Washington, DC: The National Academies Press, 1996.
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C
Reservoir Characterization
Reservoirs range from simple to complex based on their geologic origins. All reservoirs are characterized by some degree of heterogeneity (variability) of properties (porosity, permeability, fluid saturations, etc.) on a variety of scales (Figure C.1). The more complex a reservoir is, the higher its degree of heterogeneity and the more difficult it is to predict the occurrence and producibility of hydrocarbons. Reservoir characterization therefore is necessary in order to understand and predict the occurrence and producibility of hydrocarbons from a reservoir.
Reservoir characterization involves a large component of interpretation. Most producing wells are four to twelve inches in diameter, and most well logs provide constraints on data about rocks six to twelve inches away from the well bore. Therefore, wells provide information about a very small fraction of a reservoir, and hence good interpretation is needed to estimate characteristics of the vast majority of the reservoir located between wells. High-quality reservoir characterization is needed to accurately interpret data from wells and infer the distribution of flow units between wells. Techniques for reservoir characterization include core analysis, wireline log analysis, 3D reflection seismic data, crosswell tomography, vertical seismic profiles (VSPs), transient pressure analysis, tracers, 3D geological modeling, geostatistical modeling of reservoirs, production history matching, fracture analysis, and reservoir fluid analysis (PVT analyses).
Because wells provide information on such a small fraction of the res-
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C
Reservoir Characterization
Reservoirs range from simple to complex based on their geologic origins. All reservoirs are characterized by some degree of heterogeneity (variability) of properties (porosity, permeability, fluid saturations, etc.) on a variety of scales (Figure C.1). The more complex a reservoir is, the higher its degree of heterogeneity and the more difficult it is to predict the occurrence and producibility of hydrocarbons. Reservoir characterization therefore is necessary in order to understand and predict the occurrence and producibility of hydrocarbons from a reservoir.
Reservoir characterization involves a large component of interpretation. Most producing wells are four to twelve inches in diameter, and most well logs provide constraints on data about rocks six to twelve inches away from the well bore. Therefore, wells provide information about a very small fraction of a reservoir, and hence good interpretation is needed to estimate characteristics of the vast majority of the reservoir located between wells. High-quality reservoir characterization is needed to accurately interpret data from wells and infer the distribution of flow units between wells. Techniques for reservoir characterization include core analysis, wireline log analysis, 3D reflection seismic data, crosswell tomography, vertical seismic profiles (VSPs), transient pressure analysis, tracers, 3D geological modeling, geostatistical modeling of reservoirs, production history matching, fracture analysis, and reservoir fluid analysis (PVT analyses).
Because wells provide information on such a small fraction of the res-
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FIGURE C.1 Levels of reservoir heterogeneity. From: Tyler, N., 1988, New Oil from Old Fields. Geotimes vol. 33, no. 7, p. 9. Reprinted by permission of the American Geological Institute.
ervoir, integration of geophysical and engineering data with geological well information is required to give the best interpretation possible. Geophysical techniques can provide information about a large fraction of the reservoir. Conventional 3D seismic data can provide structural data for an entire reservoir, but conventional surface seismic data can only image bodies of rock approximately 100 by 100 by 100 feet. Seismic data cannot, therefore, directly provide data on many of the most important reservoir properties like porosity, permeability, and fluid saturations. And while other geophysical techniques like crosswell tomography can give much finer resolution, they also do not directly provide information on porosity, permeability, and fluid saturations. Fluid flow and pressure data from wells can provide much data on bulk properties of fluid flow within a reservoir. In general, the most accurate and comprehensive estimate of reservoir characteristics results from the integration of geologic, engineering, and geophysical data.
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TABLE C.1 GOALS OF RESERVOIR CHARACTERIZATION
MAJOR PURPOSE OF RESERVOIR CHARACTERIZATION: LOCATION OF INFILL WELLS
Project No.
Contractor
Area
Purpose
Class 1
4
Texas Bureau of Economic Geology
Frio Formation
No field demonstration
6
Diversified Operating Corporation
Sooner Field
Infill and recompletion locations
9
Sierra Energy Company
Frontier Formation
Locations of horizontal well to intersect fractures
11
University of Kansas
Savonburg and Stewart Fields
Locate infill wells and design waterflood
12
Oklahoma Geological Survey
Fluvial-dominated deltaic reservoirs in Oklahoma
Classification of reservoirs and recovery technologies being used
14
Utah Geological Survey
Bluebell Field
Locate infill wells and zones to recomplete in existing wells
Class 2
16
Fina Oil and Chemical Co.
Clearfork Reservoir
Locate infill wells and redefine waterflood **
17
Laguna Petroleum Co.
Foster and S. Cowden Fields
Locate infill wells and redefine waterflood
18
Luff Exploration Co.
Williston Basin
Locate drilling locations to utilize horizontal drains
19
Michigan Tech. University
Dundee Formation
Locate horizontal wells
23
University of Kansas
Schaben and Bindley Fields
Locate infill wells
24
Utah Geological Survey
Paradox Basin
Locate infill wells and assess viability of waterflood and CO2 flood
**Mid-term project
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MAJOR PURPOSE OF RESERVOIR CHARACTERIZATION: IMPROVED DESIGN OF A WATERFLOOD OR ADVANCED FLOODING TECHNIQUE
Project No.
Operator
Area
Purpose
Class 1
8
Lomax Exploration Co.
Green River Formation
Waterflood design
11
University of Kansas
Savonburg and Stewart Fields
Waterflood plus infill
12
Oklahoma Geological Survey
Fluvial-dominated deltaic reservoirs in Oklahoma
Classification of reservoir and recovery technologies used
13
University of Tulsa
Glen Pool Field
Waterflood
Class 2
15
Sensor
Anadarko Basin
Gel treatment
16
Fina Oil and Chemical Co.
Clear Fork Reservoir
Locate infill wells and redefine waterflood **
17
Laguna Petroleum Co.
Foster and S. Cowden Fields
Locate infill wells and redefine waterflood
20
Oxy USA, Inc.
Welch Field
Cyclic CO2 flood **
21
Phillips Petroleum Co.
South Cowden Field
Horizontal well for CO2 injection **
22
Texaco E&P, Inc.
Texaco Central Vacuum Unit
CO2 Huff-n-Puff
24
Utah Geological Survey
Paradox Basin
Locate infill wells and assess viability of waterflood and CO2 flood
**Mid-term project
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LIMITED EMPHASIS ON RESERVOIR CHARACTERIZATION
Project No.
Contractor
Area
Purpose
Class 1
2
Amoco Production Co.
West Hackberry Field
Air injection **
7
Hughes Eastern Corp.
North Blowhorn Creek Field
Microflora and waterflood **
10
Texaco E&P, Inc.
Port Neches Field
CO2 flood with horizontal and vertical wells **
** Mid-term project
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