Development Geology of the Antelope Shale:
Section 1Y, Cymric Field, San Joaquin Valley, California

ABSTRACT
The Antelope Shale reservoir in Section 1Y, Cymric Field, San Joaquin Valley, California is one of Chevron’s key assets. The reservoir is a Miocene Age member of the Monterey Formation composed of Opal A (amorphous), Opal CT (cristobalite, tridimite) and Quartz phase diatomaceous deep water sediments. The Antelope Shale has an anomalously high average porosity of 58%, high initial oil saturations of up to 60%, and low permeabilities of 3 millidarcys. Development geology skills required to process this complex reservoir and involve: obtaining, analyzing, and evaluating open hole well logs; structural mapping and correlation; fracture mapping using development geophysics; and an understanding of the diagenetic process.