Preliminary Results of Deep Drilling at Elk Hills, Kern County, California

Maurice Fishburn, George McJannet

Naval Petroleum Reserve 1 (Elk Hills) is located in the southwestern San Joaquin basin in 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 portions 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 o 24,426 ft.

In well 934-29R, several major sand units were penetrated, most of which encountered significant gas shows. In addition, a drill-stem test at 17,400 ft indicated a flow rate of 791 mcf/day with some water and condensate. Preliminary geochemical analysis of cores and cuttings indicated that the potential for hydrocarbon generation exists throughout the well with the main phase of oil generation between 12,000 and 22,000 ft and gas generation below 22,000 ft, which is significant since the possibility of hydrocarbon production exists at a greater depth than previously expected.

Successful drilling of 934-29R was attributed to the use of an oil-based mud system. The well took 917 days to drill including 9,560 rotating hours with 134 bits. The use of a turbodrill/diamond bit combination drilling assembly significantly reduced drilling time. Bottom-hole temperature was greater than 400°F. Calculated bottom-hole pressures were in excess of 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 #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.