--> --> Abstract: Chromatography Helps Optimize Development of Diatomite in the South Belridge Field, Kern County, California, by J. D. Tucker, B. A. Bell, and R. Timmer; #90992 (1993).

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TUCKER, J. D., Geo-Microbial Technologies, Inc., Ochelata, OK, B. A. BELL, Goode Core Labs, Bakersfield, CA, and ROBERT TIMMER, Mobil Exploration and Producing U.S. Inc., Bakersfield, CA

ABSTRACT: Chromatography Helps Optimize Development of Diatomite in the South Belridge Field, Kern County, California

Production in South Belridge field consists of heavy oil from shallow sands of the Tulare Formation and intermediate to light oil from the underlying diatomite of the Monterey Formation. Productivity of early diatomite wells in the southern end of the field was quite variable. Although there was a clear relationship between productivity and oil gravity, it was not possible to predict oil gravity prior to completion. Many of the very long completion intervals yielded low oil rates and marginal economics.

Analysis of sidewall cores using chromatography demonstrated that two oil types, type A and type B, could be distinguished. Type A is a highly biodegraded, heavy (12-22 degrees API) oil. High viscosity (15-1000 cp) combined with low matrix permeability in the diatomite (less than 1 md) results in poor productivity. Type B is less biodegraded and is characterized by pristane, phytane, and other lighter hydrocarbons. API gravity of type B ranges from 25 to 34 degrees, and viscosity ranges from 1 to 11 cp. Lower viscosity of type B results in improved productivity.

Comparison of chromatographic data from sidewall cores with production tests shows that the n-C17 + n-C18 to pristane + phytane ratio determined from cores can be used to select completion intervals with type B oil. Chromatographic data from several wells has been used to show that the boundary between oil types is a well-defined surface, paralleling the crest of the structure, but dipping more steeply along the flanks and nose. Identification of the light oil "fairway" has permitted optimization of well placement and completion intervals.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.