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

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
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