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AAPG Bulletin


AAPG Bulletin, V. 87, No. 3 (March 2003), P. 415-425.

Copyright 2003. The American Association of Petroleum Geologists. All rights reserved.

Trapping capacity of faults in the Eocene Yegua Formation, East Sour Lake field, southeast Texas

Jin-wook Kim,1 Robert R. Berg,2 Joel S. Watkins,3 Thomas T. Tieh4

1Naval Research Laboratory, Stennis Space Center, Mississippi 39529; email: jkimnrlssc.navy.mil
2Department of Geology & Geophysics, Texas A&M University, College Station, Texas 77843; email: berggeo.tamu.edu
3Department of Geology & Geophysics, Texas A&M University, College Station, Texas 77843; email: jwatkinsgeo.tamu.edu
4Department of Geology & Geophysics, Texas A&M University, College Station, Texas 77843; email: tiehgeo.tamu.edu


Jin-wook Kim specializes in interactions between microbes and clay minerals, evolution of pelitic rocks over the range of burial diagenesis to low-grade metamorphism, shale microstructure, and shale seal analysis. He has also worked on the integrated study of the migration and entrapment of hydrocarbons focusing on the shale sealing properties such as capillary pressure and permeability.

Robert R. Berg formerly held the Michel T. Halbouty Chair in Geology at Texas A&M University. His teaching experience of 31 years was preceded by 16 years of practice as an exploration geologist and geophysicist. His research has concentrated on sandstone reservoir characterization, capillary trapping, and hydrodynamic effects on oil accumulations. In 1988, he was elected to the National Academy of Engineering, and in 1993, he was the AAPG Sidney Powers Medalist.

Joel S. Watkins specializes in integrated multidisciplinary studies of petroliferous basins. He has 8 years of experience in the oil industry including 2 years as an exploration manager and 2 years as a vice-president with Gulf Oil. He has designed seismic equipment for use on the moon, spent 5 years collecting, processing, and interpreting marine seismic data and served as Co-Chief Scientist on Deep Sea Drilling Project Leg 66.

Thomas Ta-pin Tieh's primary teaching for 33 years and research interests are in the mineralogy and geochemistry of clastic sedimentary materials under conditions of weathering and diagenesis and their effects on the development of energy and mineral resources and environmental quality. He received a B.S. degree from the University of Illinois, and an M.S. degree and Ph.D. from Stanford University.


We thank S. Agar, R. Davies, J. Handschy, and R. Knipe for their critical reviews of the manuscript. We acknowledge financial support from Integrated Reservoir Investigation Group (IRIG) at Texas A&M University. CORE/NRL Postdoctoral Fellowship in part funded this work (J. Kim). NRL Contribution No. 7430-02-6.


The properties of a sheared zone in the Eocene Yegua Formation were investigated to evaluate the trapping capacity of faults. An 11-m core of Yegua sandstone at a depth of 3029 m shows highly sheared bedding and increasing dip from 10 to 30 with depth. Porosity and permeability of the sheared zone range from 10 to 12% and 1 to 5 md, respectively (about 10–16% of porosity reduction and 29–60 md of permeability reduction). Most pores in this sandstone are of secondary origin. Pores in the sheared zone were deformed and collapsed because of clay smears and shear. Physical characters of sheared zones were investigated by optical and scanning electron microscopy (SEM). A reduction of porosity and permeability with depth approaching the sheared zones created a capillary barrier that prevents hydrocarbon drainage and compartmentalized the reservoir. Initial oil/water, capillary displacement pressure of the sheared zone is 100 psi (6.89105 Pa), sufficient to trap an average oil column of 210 m and gas column of 70 m.

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