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Title: Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir

Abstract

Natural fractures exert a strong influence over oil production in Spraberry Trend Area reservoirs in the Permian Basin of west Texas. The importance of the fracture network has been known since the 1950s, but until recently, there has been very little detailed study of the fractures themselves. In 1996, a horizontal Spraberry well was cored as part of a DOE Class III Field Demonstration Project. Fractures from the horizontal core as well as other fractures encountered in vertical Spraberry cores were analyzed in detail for information on both large scale features including orientation and spacing and small-scale features such as the relationships between fracture mineralization and matrix rock composition. At least three sets of fractures are found within the upper and middle Spraberry cores. These sets have distinct orientations, spacing, mineralization, distribution with respect to lithology, and surface characteristics (Lorenz, 1997). Fractures found in the 1U zone of the upper Spraberry have a NE strike, and tend to be partly mineralized with barite, quartz, and dolomite. Distribution of these mineral phases can greatly affect conductivity between the fractures and the rock matrix. The 5U zone of the upper Spraberry contains fractures with NNE and ENE orientations. The NNE set ofmore » fractures has stepped fracture surfaces indicating a shear origin, and minor amounts of quartz and dolomite mineralization. The ENE fracture set has smooth planar surfaces of tension origin with some calcite mineralization present. Natural fractures in black shales overlying both the 1U and the 5U have an ENE orientation similar to unmineralized fractures in the 5U. No fractures were encountered in similar shales underlying reservoir zones. A set of hairline fractures, most completely healed with calcite cement was also found in some Middle Spraberry cores. The unique nature of each of these fracture sets implies that fracturing probably occurred as several separate events and indicates that the Spraberry Formation has undergone a more complex stress history than might be construed from its fairly flat-lying nature.« less

Authors:
Publication Date:
Research Org.:
Federal Energy Technology Center, Morgantown, WV, and Pittsburgh, PA
Sponsoring Org.:
USDOE
OSTI Identifier:
2207
Report Number(s):
DE-FC22-95BC14942-07
ON: DE00002207
DOE Contract Number:
FC22-95BC14942
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; Fractures; Petroleum; Texas; Enhanced Recovery

Citation Formats

David S. Schechter. Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir. United States: N. p., 1997. Web. doi:10.2172/2207.
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David S. Schechter. Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir. United States. doi:10.2172/2207.
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David S. Schechter. Wed . "Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir". United States. doi:10.2172/2207. https://www.osti.gov/servlets/purl/2207.
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@article{osti_2207,
title = {Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir},
author = {David S. Schechter},
abstractNote = {Natural fractures exert a strong influence over oil production in Spraberry Trend Area reservoirs in the Permian Basin of west Texas. The importance of the fracture network has been known since the 1950s, but until recently, there has been very little detailed study of the fractures themselves. In 1996, a horizontal Spraberry well was cored as part of a DOE Class III Field Demonstration Project. Fractures from the horizontal core as well as other fractures encountered in vertical Spraberry cores were analyzed in detail for information on both large scale features including orientation and spacing and small-scale features such as the relationships between fracture mineralization and matrix rock composition. At least three sets of fractures are found within the upper and middle Spraberry cores. These sets have distinct orientations, spacing, mineralization, distribution with respect to lithology, and surface characteristics (Lorenz, 1997). Fractures found in the 1U zone of the upper Spraberry have a NE strike, and tend to be partly mineralized with barite, quartz, and dolomite. Distribution of these mineral phases can greatly affect conductivity between the fractures and the rock matrix. The 5U zone of the upper Spraberry contains fractures with NNE and ENE orientations. The NNE set of fractures has stepped fracture surfaces indicating a shear origin, and minor amounts of quartz and dolomite mineralization. The ENE fracture set has smooth planar surfaces of tension origin with some calcite mineralization present. Natural fractures in black shales overlying both the 1U and the 5U have an ENE orientation similar to unmineralized fractures in the 5U. No fractures were encountered in similar shales underlying reservoir zones. A set of hairline fractures, most completely healed with calcite cement was also found in some Middle Spraberry cores. The unique nature of each of these fracture sets implies that fracturing probably occurred as several separate events and indicates that the Spraberry Formation has undergone a more complex stress history than might be construed from its fairly flat-lying nature.},
doi = {10.2172/2207},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Dec 17 00:00:00 EST 1997},
month = {Wed Dec 17 00:00:00 EST 1997}
}
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Technical Report:
View Technical Report (1.98 MB)
DOI:  10.2172/2207
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  • ;
    The overall goal of this project was to assess the economic feasibility of CO2 flooding the naturally fractured Spraberry Trend Area in West Texas. This objective was accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, (3) analytical and numerical simulation of Spraberry reservoirs, and, (4) experimental investigations on CO2 gravity drainage in Spraberry whole cores. Additionally, a ten (10) acre field demonstration pilot project is part of this project. This report discusses the activity, during the third calendar quarter (July through September) of 1998more » (fourth quarter of the projects fiscal year).« less

  • The objective of the Spraberry CO{sub 2} pilot project is to determine the technical and economic feasibility of continuous CO{sub 2} injection in the naturally fractured reservoirs of the Spraberry Trend. In order to describe, understand, and model CO{sub 2} flooding in the naturally fractured Spraberry reservoirs, characterization of the fracture system is a must. Additional reservoir characterization was based on horizontal coring in the second year of the project. In addition to characterization of natural fractures, horizontal coring has confirmed a previously developed rock model for describing the Spraberry Trend shaly sands. A better method for identifying Spraberry paymore » zones has been verified. The authors have completed the reservoir characterization, which includes matrix description and detection (from core-log integration) and fracture characterization. This information is found in Section 1. The authors have completed extensive imbibition experiments that strongly indicate that the weakly water-wet behavior of the reservoir rock may be responsible for poor waterflood response observed in many Spraberry fields. The authors have also made significant progress in analytical and numerical simulation of performance in Spraberry reservoirs as seen in Section 3. They have completed several suites of CO{sub 2} gravity drainage in Spraberry and Berea whole cores at reservoir conditions and reported in Section 4. The results of these experiments have been useful in developing a model for free-fall gravity drainage and have validated the premise that CO{sub 2} will recover oil from tight, unconfined Spraberry matrix.« less

  • ;
    The goal of this project was to assess the economic feasibility of CO2 flooding the naturally fractured Spraberry Trend Area in west Texas. This objective was accomplished through research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interactions in the reservoirs, (3) reservoir performance analysis, and (4) experimental investigations on CO2 gravity drainage in Spraberry whole cores. This provides results of the final year of the six-year project for each of the four areas.

  • Progress has been made in the area of laboratory analysis of Spraberry oil/brine/rock interactions during this quarter. Water imbibition experiments were conducted under ambient conditions, using cleaned Spraberry cores, synthetic Spraberry reservoir brine, and Spraberry oil. It has been concluded that the Spraberry reservoir cores are weakly water-wet. The average Amott wettability index to water is about 0.55. The average oil recovery due to spontaneous water imbibition is about 50% of original oil in place.

  • The objective of this research and the pilot project planned is to test the feasibility of CO{sub 2} for recovering oil from the naturally fractured Spraberry Trend Area in the Midland Basin. This notoriously marginal reservoir has confounded operators for 40 years with rapid depletion, low recovery during primary, disappointing waterflood results and low ultimate recovery. Yet, the tremendous areal coverage and large amount of remaining oil (up to 10 Bbbl) warrants further investigation to expend all possible process options before large numbers of Spraberry wellbores need to be plugged and abandoned. CO{sub 2} injection on a continuous, pattern widemore » basis has not been attempted in the Spraberry Trend. This is due to the obvious existence of a network of naturally occurring fractures. However, it has become clear in recent years that neglecting CO{sub 2} injection as an option in fractured reservoirs may overlook potential projects which may be viable. The 15 well pilot filed demonstration and supporting research will provide the necessary information to quantify the conditions where by CO{sub 2} flooding would be economic in the Spraberry Trend. Technical progress for this quarter is described for field and laboratory experiments.« less