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ABSTRACT: Computer-Aided Mapping Unravels Complex Geology

Jennifer J. Pence

Using a Conoco geoscience workstation, a detailed field study delineated the geology of the San Miguelito field, Ventura County, California. The field, with over 400 deviated well bores, was a prime candidate for computerization. Geologically, the Padre Juan thrust fault zone separates the field into subthrust and superthrust blocks. The turbidite sands of the Pliocene lower Pico and Repetto formations and the Miocene Santa Margarita Formation are folded and faulted into anticlinal structures in both fault blocks. In turn, these steeply dipping beds are further divided by minor faults, permeability barriers, and stratigraphic pinch-outs.

Computer mapping of 19 reservoir sands defined the structure and net pay of the field. Necessary input data included kelly bushing elevations, surface locations, deviation surveys, and reservoir sand top and bottom depths. When all data was input, the workstation gridded and contoured the corrected structural elevations for 19 horizons. Fault plane maps were intersected with each mapped horizon to delineate the fault pattern in each reservoir. Structure maps were then subtracted by the computer for true vertical thickness determinations. A net pay/gross sand ratio was multiplied by the true vertical thickness determinations. The ratio was multiplied by the true vertical thickness to yield net pay numbers. Net pay maps were contoured, gridded, and analyzed for volumetric oil in place b the workstation.

Workstations can be used to correct deviation well-bore data, to reduce the time spent mapping and calculating volumes, and to greatly improve the understanding of reservoirs. With improved understanding, improved recovery is possible.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990