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ABSTRACT: Significant Results of Deep Drilling at Elk Hills, Kern County, California

Maurice D. Fishburn

Naval Petroleum Reserve 1 (Elk Hills) is located in the southwestern San Joaquin basin, one of the most prolific oil-producing areas in the United States. Although the basin is in a mature development stage, the presence of favorable structures and high-quality source rocks continue to make the deeper parts of the basin, specifically Elk Hills, an inviting exploration target. Of the three deep tests drilled by the United States Department of Energy since 1976, significant geologic results were achieved in two wells. Well 987-25R reached low-grade metamorphic rock at 18,761 ft after penetrating over 800 ft of salt below the Eocene Point of Rocks Sandstone. In well 934-29R, the deepest well in California, Cretaceous sedimentary rocks were encountered at a total depth of 24, 26 ft.

In well 934-29R, several major sand units were penetrated, most of which encountered significant gas shows. Minor amounts of gas with no water were produced below 22,000 ft. In addition, production tests at 17,000 ft produced 46° API gravity oil. Geochemical analysis of cores and cuttings indicated that the potential for hydrocarbon generation exists throughout the well and is significant because the possibility of hydrocarbon production exists at a greater depth than previously expected. A vertical seismic profile in the well indicated that basement at this location is at approximately 25,500 ft.

Successful drilling of well 934-29R was attributed to the use of an oil-based mud system. The well took 917 days to drill, including 9,560 rotating hr with 134 bits. Bottom-hole temperature was 431°F and pressures were approximately 18,000 psi. The high overburden pressure at 24,000 ft created drilling problems that ultimately led to the termination of drilling at 24,426 ft.

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