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Abstract

G. M. Grammer, P. M. ldquoMitchrdquo Harris, and G. P. Eberli, 2004, Integration of outcrop and modern analogs in reservoir modeling: AAPG Memoir 80, p. 191-214.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Reservoir Characterization in the San Andres Formation of Vacuum Field, Lea County, New Mexico: Another Use of the San Andres Algerita Outcrop Model For Improved Reservoir Description

Emily L. Stoudt,1 Michael A. Raines2

1University of Texas Permian Basin, Midland, Texas, U.S.A.
2Kinder Morgan CO2 Co., Midland, Texas, U.S.A.

ACKNOWLEDGMENTS

The authors thank Texaco North American Producing for use of cores and other data from the Vacuum–Grayburg–San Andres unit and Central Vacuum unit, for permission to publish, and for financial contributions for the color pages. We are deeply indebted to C. Kerans and F. J. Lucia from the University of Texas Bureau of Economic Geology for their continued advice, information, and support during our efforts to correlate our Vacuum San Andres with their outcrop data. We also thank the Bureau of Economic Geology for supplying digital copies of several of Kerans' figures for our use in this publication. V. French, the Texaco CO2 asset team geologist at Vacuum field, supplied additional materials and information on field performance. G. Hinterlong, another Texaco CO2 team geologist, was invaluable in helping the senior author create the Geoplus Petra figures used for determining field-to-outcrop correlations and illustrations in this paper.

ABSTRACT

Since its discovery in 1929, Vacuum field, Lea County, New Mexico has produced 361 million bbl of oil and 298 bcf of gas from the Leonardian–Guadalupian (Permian) San Andres Formation. Despite this impressive performance, 65–70% of the estimated original oil in place remains in the ground. Complex variations in the porosity and permeability of reservoir lithologies are the principal causes for incomplete hydrocarbon recovery. Dolomitized oolitic-peloidal and fusulinid-peloidal packstones and grainstones constitute the productive reservoir facies. Interbedded in these porous units are tight, anhydritic or quartzose dolomudstones to mud-rich dolopackstones and dolomitic sandstones. Cores recovered from the nonporous intervals reveal textures, fabrics, and grain types indicative of (1) deposition in tidal-flat (peritidal) environments or (2) diagenetic modification, including collapse breccias, sinkholes, caves, and vertical fractures plugged with quartz sand or anhydrite cement, suggestive of exposure (karst) overprinting.

Early geologic models of the Vacuum field were primarily generated from petrophysical data, resulting in lithostratigraphic correlations that crossed time lines and flow units. Application of a chronostratigraphic framework for the San Andres based on outcrop studies results in an updated reservoir model for Vacuum field. Improvements include (1) recognition of localized, tight, tidal-flat cycles in separate horizons in the youngest San Andres high-frequency sequence (HFS) instead of correlating all nonporous, high gamma-ray intervals as a single, regional quartzose sandstone (Lovington sand), (2) identification of bypassed pay in porous, strike-parallel dolopackstones that are stratigraphically equivalent to, but downdip from, the tidal flats, and (3) recognition of the presence of tight karst intervals in older HFSs that compartmentalize the most continuous San Andres pay interval. Deeper, uncored San Andres lithologies can be more accurately characterized by comparing petrophysical information with facies attributes from older San Andres outcrops. An untested reservoir may occur in basal San Andres skeletal dolopackstones that are sealed by dolomudstones.

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