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BURN, MARK J., Bureau of Economic Geology, University of Texas at Austin, Austin, TX, MARK A. SIPPEL, Research and Engineering Consultants, Inc., Englewood, CO, JOSE VIDAL, ResTech, Inc., Houston, TX, JIM R. BALLARD, Envirocorp Services & Technology, Inc., Houston, TX, RAY A. LEVEY, University of Texas at Austin, Austin, TX, and PAUL KNOWLES, Anaqua Oil and Gas, Inc., Corpus Christi, TX

ABSTRACT: Identification and Evaluation of Bypassed and Incompletely Drained Gas Reservoirs in the Wave-Dominated Deltaic System of the Frio Formation (Oligocene), North McFaddin Field, Victoria County, South Texas

An integrated geologic, engineering, and petrophysical evaluation of North McFaddin field, undertaken in cooperation with the current operator, Anaqua Oil and Gas, Inc., targeted actual and potential secondary natural gas resources within thin reservoirs (typically 5-15 ft thick). Funded by the Gas Research Institute, the U.S. Department of Energy, and the State of Texas, this research forms part of the Secondary Gas Recovery project of the Bureau of Economic Geology.

Improved vertical resolution of recently developed wireline tools and advances in well-log analytical techniques have been fundamental in identifying these resources. Reservoirs are vertically compartmentalized by nonreservoir facies of subequal thicknesses and collectively are grouped into sequences 75-100 ft thick. Individual reservoirs typically form laterally discontinuous lobes (5000-6000 ft wide) of variable elongation and orientation with respect to inferred depositional dip. Reservoir facies are interpreted to be of distal shoreface origin.

Contour maps of net sandstone thickness, relative spontaneous potential deflection, and resistivity were superposed for each reservoir unit. These data were integrated with structure maps and well-test production, wireline-formation test, and sidewall-core data, allowing the potentially productive limits of each reservoir unit to be delineated. By comparing subsequently determined volumes of original gas in place with historical production data, potentially recoverable reserves were estimated to be as much as 1000 mmcf for individual reservoirs. These procedures enabled not only the recommendation of recompletion targets, but also suggested a strategic location for a potential development well.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.