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Title: San Andres dolomite reservoir, Emma field, Andrews County, Texas: Depositional facies and diagenesis

Abstract

Although nearly 100% (19 million bbl of oil) of the estimated recoverable oil in the Emma San Andres reservoir has been produced, indications are that as much as 15 million bbl of recoverable, movable oil remains. Detailed study of facies and diagenesis in the reservoir reveals considerable lateral and vertical variability, which has important implications for recovery and injection efficiencies in the field. The upper San Andres Formation in the Emma field comprises a shallowing-upward sequence of pervasively dolomitized, shallow-water subtidal to supratidal carbonates that accumulated on a gently east-sloping ramp. The lowermost part of the reservoir interval is composed of laterally extensive fusulinid packstone deposited in an open-marine ramp setting. Abruptly overlying this facies is a sequence of interbedded fusulinid/algal grainstone, formed in a migrating sand-shoal complex, and burrowed, skeletal mudstone deposited on a restricted inner ramp. The grainstone is restricted to the western and central parts of the field. These deposits are overlain by pisolitic and cryptalgal mudstones and terrigenous siliciclastics of supratidal origin. Anydrite is abundant throughout the section. Porosity and permeability are facies controlled. Highest permeabilities are developed in shoal complex grainstone (100 md) and in fusulinid packstone (925-50 md). Lateral and vertical facies variations resultedmore » in considerable reservoir heterogeneity. Trace-element and isotope data indicate that most of the San Andres dolomite and associated sulfate (anhydrite) precipitated from downward-moving, seawater-derived brines during shallow burial in the late Guadalupian. Subsequent anhydrite dissolution has locally enhanced original porosity.« less

Authors:
 [1]
  1. (Bureau of Economic Geology, Austin, TX (USA))
Publication Date:
OSTI Identifier:
5429274
Alternate Identifier(s):
OSTI ID: 5429274
Report Number(s):
CONF-8703189--
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA); Journal Volume: 71:2; Conference: American Association of Petroleum Geologists Southwest Section convention, Dallas, TX (USA), 22-24 Mar 1987
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; OIL FIELDS; RESERVOIR ROCK; DIAGENESIS; TEXAS; CARBONATE ROCKS; DEPOSITION; DOLOMITE; GEOLOGIC FORMATIONS; GEOLOGIC HISTORY; GEOLOGIC MODELS; PERMEABILITY; POROSITY; 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

Ruppel, S.C.. San Andres dolomite reservoir, Emma field, Andrews County, Texas: Depositional facies and diagenesis. United States: N. p., 1987. Web.
Ruppel, S.C.. San Andres dolomite reservoir, Emma field, Andrews County, Texas: Depositional facies and diagenesis. United States.
Ruppel, S.C.. Sun . "San Andres dolomite reservoir, Emma field, Andrews County, Texas: Depositional facies and diagenesis". United States. doi:.
@article{osti_5429274,
title = {San Andres dolomite reservoir, Emma field, Andrews County, Texas: Depositional facies and diagenesis},
author = {Ruppel, S.C.},
abstractNote = {Although nearly 100% (19 million bbl of oil) of the estimated recoverable oil in the Emma San Andres reservoir has been produced, indications are that as much as 15 million bbl of recoverable, movable oil remains. Detailed study of facies and diagenesis in the reservoir reveals considerable lateral and vertical variability, which has important implications for recovery and injection efficiencies in the field. The upper San Andres Formation in the Emma field comprises a shallowing-upward sequence of pervasively dolomitized, shallow-water subtidal to supratidal carbonates that accumulated on a gently east-sloping ramp. The lowermost part of the reservoir interval is composed of laterally extensive fusulinid packstone deposited in an open-marine ramp setting. Abruptly overlying this facies is a sequence of interbedded fusulinid/algal grainstone, formed in a migrating sand-shoal complex, and burrowed, skeletal mudstone deposited on a restricted inner ramp. The grainstone is restricted to the western and central parts of the field. These deposits are overlain by pisolitic and cryptalgal mudstones and terrigenous siliciclastics of supratidal origin. Anydrite is abundant throughout the section. Porosity and permeability are facies controlled. Highest permeabilities are developed in shoal complex grainstone (100 md) and in fusulinid packstone (925-50 md). Lateral and vertical facies variations resulted in considerable reservoir heterogeneity. Trace-element and isotope data indicate that most of the San Andres dolomite and associated sulfate (anhydrite) precipitated from downward-moving, seawater-derived brines during shallow burial in the late Guadalupian. Subsequent anhydrite dissolution has locally enhanced original porosity.},
doi = {},
journal = {AAPG Bulletin (American Association of Petroleum Geologists); (USA)},
number = ,
volume = 71:2,
place = {United States},
year = {Sun Feb 01 00:00:00 EST 1987},
month = {Sun Feb 01 00:00:00 EST 1987}
}

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  • In the Shafter Lake field area, the San Andres contains 14 depositional cycles, consisting of upward-shoaling progradational sequences of subtidal, intertidal, and supratidal deposits. The deposits can be correlated between the two cores located 2 mi apart along the depositional strike. Six of the cycles are capped by supratidal deposits and are essentially complete, whereas eight were subjected to erosional truncation, which generally excavated supratidal and intertidal deposits. Thus, the San Andres reflects a complex eustatic history. The San Andres consists entirely of dolostones, the diagenesis of which records the following multicyclic stages: (1) dolomitization; (2) emplacement of anhydrite asmore » cement, replacement, or a combination of cement and replacement; (3) dissolution of anhydrite or its alteration by gypsum, hemihydrate, or calcite. Many intervals record at least two complete diagenetic cycles (six stages). Three types of primary porosity were formed initially: intergranular, intrabiotic, and fenestral voids. Secondary pore types include intercrystalline pores, biomolds, and fractures. Varieties of tertiary pores are anhydrite porphryoblast models and intracrystalline voids. A previously undescribed variety of intracrystalline porosity was observed. A medial area between the dolomite crystal core and the outer rim was dissolved to create a moat-like pore. The principal occluders of all pore types are dolomite and anhydrite cements. The best effective porosity zones are preserved in subtidal facies wherein intercrystalline and intracrystalline pores, biomolds, and anhydrite porphyroblast molds are interconnected.« less
  • The Mallet Lease, Hockley County, western Texas, produces oil from the Permian San Andres Dolomite as part of the larger Slaughter Field. The Mallet Lease is being considered for infill drilling and for tertiary recovery. This paper discusses the engineering and geologic basis of the reservoir description that is used in history matching 40 years of primary and secondary performance. Emphasis is given to integration of reservoir description with necessary fluid flow properties needed to match performance and also the use of long term data to insure proper reservoir representation. There are no discontinuous, isolated portions of the reservoir thatmore » would be tapped by infill wells. Most of the remaining oil is located in the tighter portions of the producing intervals which bears on prospects for infill drilling and tertiary oil recovery.« less
  • The Mallet Lease in W. Texas produces oil from the Permian San Andres Dolomite as part of the larger Slaughter field. The Mallet Lease is being considered for infill drilling and for tertiary recovery. This work discusses the engineering and geologic basis of the reservoir description that is used in history matching 40 yr of primary and secondary performance. Emphasis is given to integration of reservoir description with necessary fluid flow properties needed to match performance and also the use of long term data to insure proper reservoir representation. There are no discontinuous, isolated portions of the reservoir that wouldmore » be tapped by infill wells. Most of the remaining oil is located in the tighter portions of the producing intervals which bears on prospects for infill drilling and tertiary oil recovery. 11 references.« less
  • The Mallet Lease, Hockley County, western Texas, produces oil from the Permian San Andres Dolomite as part of the larger Slaughter Field. The Mallet Lease is being considered for infill drilling and for tertiary recovery. This paper discusses the engineering and geologic basis of the reservoir description that is used in history matching 40 years of primary and secondary performance. Emphasis is given to integration of reservoir description with necessary fluid flow properties needed to match performance and also the use of long term data to insure proper reservoir representation. There are no discontinuous, isolated portions of the reservoir thatmore » would be tapped by infill wells. Most of the remaining oil is located in the tighter portions of the producing intervals which bears on prospects for infill drilling and tertiary oil recovery.« less
  • Cyclic San Andres facies have been delineated for the Reeves field. Diagnostic facies criteria were established from thin sections and core chips. The Reeves zone occurs about 500 ft below the top of the San Andres Formation and consists of 4 sedimentary cycles, each between 10 and 20 ft thick. Numerous sedimentary structures can be recognized in the Reeves zone which are characteristic of supratidal deposition. The carbonate grain types are also characteristic of shallow-water deposition. Concentric oolites and coated grains are the most common, followed in abundance by pellets, skeletal grains, lumps, and intraclasts. Several varieties of anhydrite includemore » nodular anhydrite, void-filling anhydrite, replacement anhydrite, and euhedral anhydrite laths. Porosity variations are related to original sedimentary facies and their diagenesis. Oolitic grainstone porosity has been plugged with anhydrite. Productive porosity generally occurs in the wackestone facies, and it is either intercrystalline, leached or fractured origin. (12 refs.)« less