Geology and production characteristics of fractured reservoirs in the Miocene Monterey formation, West Cat Canyon oilfield, Santa Maria valley, California.

Abstract

The West Cat Canyon oil field produces from fractured diagenetic dolomites of the Monterey formation. Original Monterey sediments have depositional and stratigraphic similarities to modern deep-marine, anoxic deposits of the Gulf of California. Applying this analogue to diagenetic alterations suggests that Monterey dolomites formed initially within the zone of methanogenesis and continued with burial whereby 12C became more prevalent via thermocatalytic reactions. Nucleation of Monterey matrix dolomites commonly involved liquid or gaseous hydrocarbons. Fracturing of Monterey dolomite appears to have been initiated by dilatancy under tectonic compression together with elevated pore pressures. The post-dilation mechanism of rupture and brecciation appears to have been natural hydraulic or petroleum fluid fracturing. The latter requires that adequate depth of burial and petroleum maturation T be attained.-J.M.H.