Abstract: Geological Aspects of Drilling Horizontal Wells in Steam Flood Reservoirs, West Side, Southern San Joaquin Valley, California

D. D. Crough, M. L. Holman, J. J. Sande

Shell Western E&P Inc. has drilled 11 horizontal wells in four mature steam floods in the Coalinga, South Belridge, and Midway-Sunset fields. Two medium radius wells are producing from the Pliocene Etchegoin Formation in Coalinga. One medium radius well is producing from the Pleistocene Tulare Formation in South Belridge field. Three short radius and five medium radius wells are producing from the upper Miocene, Sub-Hoyt and Potter sands in Midway-Sunset field. Horizontal wells at the base of these reservoirs and/or structurally downdip near the oil-water contact are ideally suited to take advantage of the gravity drainage production mechanism. Reservoir studies and production experience have shown these horizontal wells should increase reserves, improve recovery efficiency, impro e the oil-steam ratio, and improve project profitability.

Geological considerations of targeting the wells vary between fields because of the different depositional environments and resulting reservoir characteristics. The thin sands and semicontinuous shales in the Tulare Formation and the Etchegoin Formation require strict structural control on the top and base of the target sand. In the Sub-Hoyt and Potter sands, irregularities of the oil-water contact and sand and shale discontinuities must be understood. Logging and measurement while drilling provide geosteering capability in medium radius wells. Teamwork between all engineering disciplines and drilling and producing operations has been critical to horizontal well success.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994