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Title: The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas

Abstract

The Permian San Andres Formation represents one of the most prolific hydrocarbon-producing intervals of the Permian basin. Dolostone lithofacies intercalated with thin evaporites accommodate highly compartmentalized reservoirs resulting from complex depositional and diagenetic histories. This compartmentalization often facilitates the use of these reservoirs in flow-unit studies. Perhaps more important than the relationship of productive intervals to depositional facies is the degree to which diagenetic processes have influenced reservoir properties. Detailed petrographic evaluation of the reservoir in question, though often overlooked, should be an integral part of flow-unit studies. Once a diagenetic sequence is established, the information may be incorporated in to the facies model to better understand how to subdivide the reservoir. Such an investigation has been conducted on the San Andres Formation in Reeves field of southeastern Yoakum County, Texas. Here, multistage diagenetic overprints are superimposed on depositional facies that vary in degree of lateral extent, thereby complicating the geometries of individual productive zones within the reservoir. Analysis of the reservoir reveals that Reeves San Andres sediments were subjected to dominant diagenetic processes, including dolomitization and sulfate implacement, both of which are major factors in porosity preservation, and a variety of minor processes that have had little effect onmore » reservoir quality. The recognition of diagenetic facies, and understanding of the processes that have created them, and identification of the implications of these processes on reservoir properties is a vital part of any flow-unit study.« less

Authors:
 [1]
  1. (Texas Tech Univ., Lubbock, TX (United States))
Publication Date:
OSTI Identifier:
6944276
Report Number(s):
CONF-9404148--
Journal ID: ISSN 0149-1423; CODEN: AABUD2
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States); Journal Volume: 78:3; Conference: American Association of Petroleum Geologists (AAPG) Southwest Section meeting, Ruidoso, NM (United States), 24-26 Apr 1994
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; FLUID FLOW; GEOLOGIC MODELS; OIL FIELDS; PRODUCTIVITY; RESERVOIR ROCK; DEPOSITION; PHYSICAL PROPERTIES; SEDIMENTS; DIAGENESIS; TEXAS; EVALUATION; EVAPORITES; HYDROCARBONS; PERMIAN BASIN; POROSITY; SEDIMENTARY BASINS; ZONES; DEVELOPED COUNTRIES; GEOLOGIC DEPOSITS; GEOLOGIC STRUCTURES; MINERAL RESOURCES; NORTH AMERICA; ORGANIC COMPOUNDS; PETROLEUM DEPOSITS; RESOURCES; ROCKS; SEDIMENTARY ROCKS; USA 020200* -- Petroleum-- Reserves, Geology, & Exploration

Citation Formats

Henderson, S. The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas. United States: N. p., 1994. Web.
Henderson, S. The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas. United States.
Henderson, S. 1994. "The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas". United States. doi:.
@article{osti_6944276,
title = {The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas},
author = {Henderson, S.},
abstractNote = {The Permian San Andres Formation represents one of the most prolific hydrocarbon-producing intervals of the Permian basin. Dolostone lithofacies intercalated with thin evaporites accommodate highly compartmentalized reservoirs resulting from complex depositional and diagenetic histories. This compartmentalization often facilitates the use of these reservoirs in flow-unit studies. Perhaps more important than the relationship of productive intervals to depositional facies is the degree to which diagenetic processes have influenced reservoir properties. Detailed petrographic evaluation of the reservoir in question, though often overlooked, should be an integral part of flow-unit studies. Once a diagenetic sequence is established, the information may be incorporated in to the facies model to better understand how to subdivide the reservoir. Such an investigation has been conducted on the San Andres Formation in Reeves field of southeastern Yoakum County, Texas. Here, multistage diagenetic overprints are superimposed on depositional facies that vary in degree of lateral extent, thereby complicating the geometries of individual productive zones within the reservoir. Analysis of the reservoir reveals that Reeves San Andres sediments were subjected to dominant diagenetic processes, including dolomitization and sulfate implacement, both of which are major factors in porosity preservation, and a variety of minor processes that have had little effect on reservoir quality. The recognition of diagenetic facies, and understanding of the processes that have created them, and identification of the implications of these processes on reservoir properties is a vital part of any flow-unit study.},
doi = {},
journal = {AAPG Bulletin (American Association of Petroleum Geologists); (United States)},
number = ,
volume = 78:3,
place = {United States},
year = 1994,
month = 3
}

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  • The Permian San Andres reservoir at Roberts unit produces from approximately 250 ft of anhydritic dolostones. The reservoir interval, which is more than 500 ft below the top of the San Andres Formation, consists of fossiliferous and pelletal/peloidal dolowackestones and dolopackstones. They were deposited in a shallow-marine environment with local shoaling conditions. Toward the top of the reservoir, intertidal and supratidal deposits interfinger with the subtidal units and form the lateral and overlying seals. A sponge-bryozoan bank lithofacies is recognized within the subtidal deposits at Roberts unit. The banks consist of dolomitized mud-rich boundstones dominated by bryozoans, sponges, and crinoids.more » Interbedded fossiliferous dolowackestones, dolopackstones, and dolograinstones are common. The restricted nature of the San Andres in the western part of Roberts unit (i.e., shoreward of the banks) indicates that the banks baffled wave energy and inhibited current circulation on the platform, resulting in a mud-dominated, restricted lagoonal facies with very low faunal diversity. The sponge-bryozoan banks occur within a narrow belt across the central part of Roberts unit and continue into the adjacent Willard unit. Their distribution has a distinct northeast-soutwest trend that parallels the subjacent Abo shelf margin reef trend, suggesting that the Abo reef trend influenced subsequent bank development.« less
  • Roberts unit is a mature San Andres waterflood project located in Wasson field, Yoakum County, Texas. Texaco, as operator, has evaluated the reservoir for CO{sub 2} flooding, and a four-phased CO{sub 2} project has been designed for the unit. A critical aspect of CO{sub 2} flood design is the development of geologic reservoir management, such as flood monitoring and evaluation of infill drilling. The geologic reservoir model established for the southeastern part of the unit (the CO{sub 2} Phase III area) is an example of this design. The reservoir consists of stacked carbonate depositional sequences. The cyclic nature of thesemore » depositional sequences is reflected in both core-defined lithofacies and porosity log character. Sequences consist of basal mudstones, restricted-shelf skeletal wackestones, open-shelf skeletal wackestones and packstones, solution and brecciated zones, and peloidal packstone caps. Intertidal mudstones and wackestones occur at the top of the reservoir and in the overlying reservoir seal. Porosity distribution is controlled by diagenetic events, but these events are closely related to depositional facies. Reservoir geometry and reservoir quality are interpreted from study of carbonate lithofacies, porosity and permeability relationships, and injection characteristics. Depositional sequences are subdivided into layers (flow units) for use in reservoir simulation. Log normalization, core description, porosity interpretation, reservoir mapping, three-dimensional modeling, and joint effort between project geologists and engineers contributed to development of the reservoir model.« less
  • The coring, logging and testing of Bennett Ranch Unit well No. 310 was a cooperative effort between Texas Pacific, owner of the well, and Gruy Federal, Inc. The requirements of the contract, which are summarized in Enclosure 1, Appendix A, include drilling and coring activities. The pressure-coring and associated logging and testing programs in selected wells are intended to provide data on in-situ oil saturation, porosity and permeability distribution, and other data needed for resource characterization of fields and reservoirs in which CO/sub 2/ injection might have a high probability of success. This report presents detailed information on the firstmore » such project. This project demonstrates the usefulness of integrating pressure core, log and production data to realistically evaluate a reservoir for carbon dioxide flood. The engineering of tests and analysis of such experimental data requires original thinking, but the reliability of the results is higher than data derived from conventional tests.« less
  • Wasson field, a broad, domal structure, is located on the southeastern part of the Northwest shelf. Mobil Producing Texas and New Mexico, Inc., owns and operates the 640-ac H. O. Mahoney lease on the northeast flank of Wasson field. The lease produces from the Permian San Andres, Clear Fork, and Wichita-Albany Formations. The San Andres is a dolomitized carbonate deposited in an arid, tidal-flat environment with subtidal through supratidal facies in a regressive, shoaling-upward sequence. Production occurs from two intervals, the First Porosity and the Main Pay. Average reservoir parameters are 193 net ft, 13% porosity, and 6.2-md permeability. Themore » first porosity interval, consisting of zones F1-F5, is 400 ft below the San Andres top and is comprised of porous supratidal and intertidal dolomites. These zones have a discontinuous, stringerlike geometry and display poorer reservoir development. The principal reservoir is the continuous Main Pay interval, which consists of zones M1-M8 and underlies the First Porosity at an average depth of 5,100 ft. The best porosity and permeability are developed within dolomitized pelloidal packstones of zones M1-M3 and F4. These packstones, deposited subparallel to the San Andres shoreline, exhibit excellent intercrystalline and leached-vuggy porosity with good permeability and lateral continuity. Understanding the depositional history allowed the identification of northeast to southwest porosity and permeability trends at Mahoney. Interbedded within the more porous zones are dolomitized mudstones displaying poor porosity and permeability. These laterally continuous layers restrict vertical fluid movement. Estimated original oil in place is 75,150 Mstb. About 80% of this volume is contained in zones F-4 and M1-M3 and represents most of the flow capacity. Carbon dioxide injection began October 17, 1985.« less
  • Core studies were undertaken to determine the facies relationships, continuity, and areal distribution of pay zones in the Denver unit, San Andres reservoir (operated by Shell Western Exploration and Production Inc.). Examination of slabs and thin sections from more than 4,000 ft of core from 19 wells provided the basis for detailed log correlation and zonation of the reservoir over the entire Denver unit. Core examination revealed a classic example of a shoaling-upward sequence where the original sedimentary environments clearly influenced the development and distribution of porosity. The resultant, highly stratified reservoir model evolved because of an interdisciplinary engineering effortmore » to describe the reservoir geometry.« less