Abstract: Geology of the South Oakley Gas Field and California's Largest Gas Well, Contra Costa County, California

BLAKE, RICHARD, Lawrence Livermore National Lab, Livermore, CA; GEORGE LAPERLE, Western Continental Operating Company, Bakersfield, CA 

The Cesa #1 gas well was drilled and completed in April 1983 by WCOC in the South Oakley Gas Field as California's largest gas well. The well penetrated nearly 400 continuous feet of gas sand in the Upper Cretaceous Third Massive Sand. WCOC ran 5-1/2" casing to a depth of 8256' and perforated the upper 320' of this sand with 1128 holes. This thick massive gas sand is trapped as an erosional remnant beneath the base Meganos Gorge unconformity. The Gorge shale fill is the primary trapping mechanism, with lateral trapping provided by faulting.

Calculations of a four-point isochronal back pressure test revealed an absolute open flow potential (AFOP) of 485,000 Mcf/d. The rate exceeded all California's gas deliveries to PG&E at the time, and was also one-half of PG&E's gas volume deliveries for all of its residential customers in California. A 165 acre production unit was formed, and the well commenced production in November 1983.

The caloric rating of the gas is 1074 BTU (dry), and the total gas and condensate sales from the well have totaled $46 million, much of which was sold when gas prices reached $3-4 per/MMBTU. Although the Cesa #1 produced at constant rates of 20,000 Mcf/d, the maximum production rates at times exceeded 41,000 Mcf/d. The Cesa #1 continues to produce, and has produced 13 BCF of gas. Total gas production from the South Oakley Field exceeds 73 BCF.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California