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Oil-Field Disposal Practices in Hydrogeologic Setting of Midway Sunset and Buena Vista Oil Fields: Review of Past Effects, Current Activities, and Future Scenarios

R. M. Sengebush, S. C. Kiser, E. J. Greenwood, R. N. Crozier, R. A. Crewdson, M. J. Wilson, B. A. Rycerski

Class 2 water disposal in the Midway Sunset and Buena Vista oil fields of Kern County, California, has been by injection and infiltration from spreading ponds into the unsaturated zone, which is typically hundreds of feet thick. Water collection is mostly through an extensive tributary network of collection ditches radiating from several disposal facility locations. The purpose of this study was to evaluate the subsurface movement of fluid in the hydrogeological environment and to determine the fate of the disposed water and its long-term impact on the area.

Research has demonstrated that significant fluid losses can occur due to evaporation as well as infiltration, and that the collection ditches represent a largely ignored source of significant fluid losses. Detailed evaluation of the entire history of produced water volumes has significantly changed the preexisting concepts of the mass balance.

The geology was mapped from the surface down to the base of the Tulare Formation (at places, 3,000 ft below surface). Because of the shallow Miocene-Pliocene production in these fields, most wells have been logged to within 100 ft of the surface. Previous attempts to describe the hydrogeologic setting have failed because the valuable data in these wells was not considered usable by hydrologists unfamiliar with electric-log interpretation. In addition to a complete E-log evaluation, all other sources of data, including cores, core descriptions, and water data were incorporated.

The hydrogeologic setting is composed of Pleistocene to recent sands and shales deposited in an alluvial fan-lacustrine delta environment. Contemporaneous regional uplift has influenced depositional patterns. The alluvial sediments in the valleys adjacent to the oil fields are moisture-deficient, typical for the arid climate of the southern San Joaquin Valley.

The results of this study include: (1) a mass balance on the produced water from sources to disposal point; (2) an assessment of the flow of water from disposal points into the subsurface; and (3) the storage capacities, filling times, and steady-state reservoir conditions of the existing and potential impacted zones.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.