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Title: Evaluation of evaporite facies as a tool for exploration, Yates Field, Texas

Abstract

Evaporites have long been recognized as the most efficient reservoir seal; however, the seal can itself serve as an exploration tool to locate subtle stratigraphic traps. By analogy with modern environments, thick massive evaporites form subaqueously in ponds (salinas) in topographic lows while sabkhas form on the subaerially exposed supratidal zone on topographic highs. Recognition of evaporite facies distribution can delineate paleotopography where sabkhas form a seal over local highs and closure is provided by salinas forming a lateral seal in lows. These relationships are illustrated by the giant Yates field (2 billion bbl reserves), situated at the southern tip of the Central basin platform in the Permian basin. The seal over the Yates reservoir (San Andres formation) is formed by the evaporites at the base of the Seven Rivers Formation (Guadalupian). Within the evaporite, two distinct depositional facies are recognized: a massive, salina-anhydrite in the central and western parts of the field; and on the east, stacked sabkha sequences consisting of sandy dolomite overlying a sharp base, grading into nodular anhydrite and capped by an erosional surface. The depositional topography on the underlying San Andres reservoir controlled the facies distribution in the basal Seven Rivers. Carbonate buildups formed onmore » the eastern side of the field, while interbedded shales and dolomites accumulated in the quiet lagoonal waters behind. Due to dewatering and compaction during early burial, the lagoons remained topographically low until early Seven Rivers time when they were finally filled with salina evaporites. The rigid shelf margin buildups remained as topographic highs over which sabkhas developed. Only 10% of the production has come from the lagoonal muds under the salinas, while 90% has been produced from the carbonate buildups under the sabkhas.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of Texas, Austin
OSTI Identifier:
5771827
Alternate Identifier(s):
OSTI ID: 5771827
Report Number(s):
CONF-870606-
Journal ID: CODEN: AABUD
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States); Journal Volume: 71:5; Conference: American Association of Petroleum Geologists annual meeting, Los Angeles, CA, USA, 7 Jun 1987
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; OIL FIELDS; EXPLORATION; RESERVOIR ROCK; GEOLOGIC TRAPS; TEXAS; DOLOMITE; EVAPORITES; GEOLOGIC FORMATIONS; SHALES; ALKALINE EARTH METAL COMPOUNDS; CALCIUM CARBONATES; CALCIUM COMPOUNDS; CARBON COMPOUNDS; CARBONATE MINERALS; CARBONATES; FEDERAL REGION VI; GEOLOGIC DEPOSITS; MAGNESIUM CARBONATES; MAGNESIUM COMPOUNDS; MINERAL RESOURCES; MINERALS; NORTH AMERICA; OXYGEN COMPOUNDS; PETROLEUM DEPOSITS; RESOURCES; ROCKS; SEDIMENTARY ROCKS; USA 020200* -- Petroleum-- Reserves, Geology, & Exploration

Citation Formats

Spencer, A.W., and Warren, J.K.. Evaluation of evaporite facies as a tool for exploration, Yates Field, Texas. United States: N. p., 1987. Web.
Spencer, A.W., & Warren, J.K.. Evaluation of evaporite facies as a tool for exploration, Yates Field, Texas. United States.
Spencer, A.W., and Warren, J.K.. Fri . "Evaluation of evaporite facies as a tool for exploration, Yates Field, Texas". United States. doi:.
@article{osti_5771827,
title = {Evaluation of evaporite facies as a tool for exploration, Yates Field, Texas},
author = {Spencer, A.W. and Warren, J.K.},
abstractNote = {Evaporites have long been recognized as the most efficient reservoir seal; however, the seal can itself serve as an exploration tool to locate subtle stratigraphic traps. By analogy with modern environments, thick massive evaporites form subaqueously in ponds (salinas) in topographic lows while sabkhas form on the subaerially exposed supratidal zone on topographic highs. Recognition of evaporite facies distribution can delineate paleotopography where sabkhas form a seal over local highs and closure is provided by salinas forming a lateral seal in lows. These relationships are illustrated by the giant Yates field (2 billion bbl reserves), situated at the southern tip of the Central basin platform in the Permian basin. The seal over the Yates reservoir (San Andres formation) is formed by the evaporites at the base of the Seven Rivers Formation (Guadalupian). Within the evaporite, two distinct depositional facies are recognized: a massive, salina-anhydrite in the central and western parts of the field; and on the east, stacked sabkha sequences consisting of sandy dolomite overlying a sharp base, grading into nodular anhydrite and capped by an erosional surface. The depositional topography on the underlying San Andres reservoir controlled the facies distribution in the basal Seven Rivers. Carbonate buildups formed on the eastern side of the field, while interbedded shales and dolomites accumulated in the quiet lagoonal waters behind. Due to dewatering and compaction during early burial, the lagoons remained topographically low until early Seven Rivers time when they were finally filled with salina evaporites. The rigid shelf margin buildups remained as topographic highs over which sabkhas developed. Only 10% of the production has come from the lagoonal muds under the salinas, while 90% has been produced from the carbonate buildups under the sabkhas.},
doi = {},
journal = {AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)},
number = ,
volume = 71:5,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1987},
month = {Fri May 01 00:00:00 EDT 1987}
}

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  • Production from the San Andres dolomite, principal reservoir unit in the Yates field, is controlled by structure and by stratigraphic variation in depositional diagenetic facies, resulting in subdivision of the field into eastside and westside areas. In the east, the upper San Andres is dominated by peloidal, fusulinid, and algal carbonate sand and gravel shoals that were deposited as an easterly prograding platform margin sequence. Carbonate lithologies in the west Yates are typically peloidal lime mudstones and wackestones with a restricted biota of dasyclad algae and gastropods, and thin interbeds of gray-green clay shale-all deposited in intertidal and lagoonal environments.more » Two general porosity groups comprise most of the matrix porosity in the San Andres Formation: (1) compact or dense vuggy and moldic dolomite (west Yates), and (2) sucrosic dolomite with fine molds and fine to coarse intergrain and intercrystal pores (east Yates). Most of the reservoir storage in the San Andres of the Yates field is in sucrosic dolomite. Fractures, vugs, and caves have greatly enhanced drainage from the highly porous reservoir rock matrix and have contributed to the remarkable high productivities of many wells drilled in the field during its early history.« less
  • Persistent speculation that caves played a key role in the high flow rates of many early wells in the Yates field (203 wells potentialed for more than 10,000 BOPD each, 26 wells for more than 80,000 BOPD each) has raised questions of why the caves exist, how many there are, and how to incorporate them into reservoir management practice. This paper describes the use of probability theory to answer these questions.
  • Yates field, which produces oil largely from Late Permian San Andres dolomites, was discovered in 1926 and logged its billionth barrel in 1985. It is remarkable for the size of its original oil in place (four billion barrels estimated) and for its early ability to produce hundreds to thousands of barrels per hour from individual wells at depths of less than 2,000 ft. The high quality of the reservoir has been related to the following geologic characteristics: (1) a broad anticline with significant closure located at the apex of regional structure which formed a trap for large volumes of primarymore » and secondary oil; (2) a vast integrated system of porosity (ranging from intergrain/intercrystal pores to joints, fractures, and small caves) that imparts high storage capacity and transmissivity to the reservoir dolomites; (3) a thick, efficient seal of anhydrite capping the reservoir sequence; and (4) high flowing pressures during much of the history of the field. The western area of the Yates field reservoir is dominated by peritidal to lagoonal mudstones and wackestones; the eastern area, by shallow subtidal packstones and grainstones. These depositional facies reflect both aggradation and eastward progradation of upper San Andres carbonates. Effective engineering management of the field has followed from a recognition of the quite different reservoir qualities in the two areas of the field and from adapting secondary and tertiary recovery techniques to constraints imposed by the geologic factors listed above.« less
  • Persistent speculations that caves played a key role in the high flow rates of many early wells in the Yates field (203 wells potentialed for more than 10,000 BOPD each, 26 wells for more than 80,000 BOPD each) has raised questions of why the caves exist, how many there are, and how to incorporate them into reservoir management practice. This paper describes the use of probability theory to answer these questions. Among the geologic factors that contributed to the remarkable early productivity of Yates are zones of karst in the upper San Andres Dolomite, the principle reservoir unit. Hundreds ofmore » infill wells drilled after unitization of the field in 1976 have provided ample data on cave numbers and patterns. These data indicate that karstification was produced by dynamic lenses of fresh water beneath a cluster of islands formed when lowering of Late Permian sea level exposed San Andres limestone to rainfall and dissolution. The seemingly random occurrences of caves can be fitted into a geologic framework of systematic karst processes to produce mappable petrophysical parameters. The most important of these predicts, in probabilistic terms, where the caves are located. The contribution of cave porosity to total reservoir porosity can also be estimated. This cave component of porosity can be displayed as a petrophysical log and manipulated in the same way as matrix porosity.« less
  • The Yates Field, discovered in Oct. 1926, is extraordinary in amount of oil produced, size of original oil accumulation, and well productivity. It has produced more than 500 million bbl of oil. It has been estimated that ultimate recovery from the reservoir will be between 1.5 and 2 billion bbl. The Yates Field reservoir, mostly dolomite, may be the largest single oil accumulation ever found in a North American carbonate. It occurs as a gentle dome with structural closure in excess of 350 ft and covers an area of about 21,700 acres. Cavernous and high matrix porosity in the reservoirmore » contributes significantly to the remarkable productivity of some wells in the field. The cavernous porosity probably is related to subaerial erosion. Both the Yates Field reservoir and its seal are of middle Permian age. The reservoir is largely marine bioclastic dolomite. The huge Yates Field reservoir oil accumulation probably resulted from favorable location relative to coarse beds and regional migration routes.« less