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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 50 (2000), Pages 167-167

Abstract: Karst Reservoir Previous HitPlayNext Hit, Cretaceous Shelf Margin Trend, Gulf of Mexico, U.S.A.

Martin D. Wensrich, S. Frank Rabbio, Edward A. Clerke, PhD


The Karst Reservoir Previous HitPlayNext Hit is one of eight clastic and carbonate plays associated with the Cretaceous Shelf-Margin Trend located in the Gulf of Mexico, U.S.A. study area. Analogs in the Permian Basin of west Texas show that karst reservoirs are developed in limestones during sea level low stands when ground water percolates through natural fractures and dissolves calcium carbonate. The presence of diagenitic anhydrite and the proximity to oil production suggests that hydrocarbons, which produce sulfuric acid during maturation are responsible for enhancing porosity and permeability. Surface mapping shows that the best karst reservoirs are associated with intersecting fractures. Reservoir porosity sizes range from vuggy to cavernous. Analogs show that hydrocarbons are trapped by a combination of structure and stratigraphy, and production rates of 1000 barrels of liquid per day are common.

The main risks associated with this Previous HitplayNext Hit are reservoir, trap, hydrocarbon type, and vertical seal. Seismic attribute Previous HitanalysisNext Hit shows that there is a low impedance and low frequency signature associated with vuggy reservoirs. Ray trace modeling shows that cavernous porosity is difficult to image on seismic data that is acquired with the typical parameters of an offshore 3D survey. Petrophysical Previous HitanalysisNext Hit of vuggy reservoir models using sonic and density logs consistently underestimate the porosity. The hydrocarbon type produced from discoveries in clastics and carbonates along the Cretaceous Shelf-Margin Trend in the Gulf of Mexico study area is dominantly gas. However, geochemical modeling shows that the target section may be more oil-prone farther to the south. The vertical seal carries a moderate to high risk, because the Gulf of Mexico received clastic influx from the Appalachians during the Jurassic and Cretaceous. An example of a Valanginian age shelf-margin incised valley and the sand-prone seismic facies signature of the valley fill illustrates this risk. Seismic examples of Karst Previous HitPlayTop prospects with cavernous and vuggy reservoirs are illustrated with high resolution 2D and 3D data in the Gulf of Mexico study area.

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Acknowledgments and Associated Footnotes

(1) Occidental Oil and Gas Company, 5 Greenway Plaza, Houston, Texas, 77227

(2) ARAMCO Services Company, Dhahran 31311, Saudi Arabia

Copyright © 2002 by The Gulf Coast Association of Geological Societies