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Diagenesis Of The Temblor Formation, Mckittrick Oil Field, California


The McKittrick oil field is located near the western edge of the San Joaquin basin approximately 60 km west of Bakersfield and just north-east of the McKittrick thrust fault. The oil field is currently producing from the Tulare, San Joaquin, Reef Ridge, Monterey, Temblor, Tumey, and Kreyenhagen Formations. Within the Temblor Formation production is mainly from the Carneros and the Phacoides sands. Samples were obtained from the California Well Sample Repository. Depths range between 2400 and 2650 meters. These were studied using petrography and with a scanning electron microscope equipped with an energy dispersive x-ray spectrometer (SEM-EDS) and a cathodo-luminescence system (SEM-CL). The Temblor Sandstones consist of fine to very coarse poorly to well sorted arkosic arenites. Detrital framework grains include sub-angular quartz, K-feldspar (microcline and orthoclase), plagioclase, and rock fragments. Three chemically distinct types of K-feldspars have been identified: Ba-free, Ba-rich, and perthite. Accessory minerals include glauconite, biotite, muscovite, magnetite, titanomagnetite, sphene, zircon, phosphate, corundum, and rutile. Diagenetic alteration includes compaction, dissolution of detrital minerals, albitization of feldspars, cementation by kaolinite, calcite and dolomite, precipitation of K-feldspar and quartz overgrowths, replacement of framework grains by calcite, alteration of volcanic rock fragments, and the alteration of biotite to pyrite and chlorite. Long, sutured, and interpenetrating grain-to-grain contacts, squashing of labiles to create pseudomatrix, and fracturing of brittle grains (quartz and feldspar) indicate significant compaction. Early formed fractures were healed by authigenic quartz, albite, and K-feldspars. Precipitation of carbonates and clays, rearranging of broken grains, and formation of pseudomatrix subsequently reduced porosity. Secondary porosity is common and formed initially by the dissolution of plagioclase (excluding albite) and volcanic fragments and later by dissolution of calcite, dolomite, and detrital K-feldspars. Oil emplacement was followed by precipitation of late pyrite framboids in pores containing both oil and clays. This suggests that continuing maturation of the hydrocarbons supplied sulfur that reacted with ferrous ions in pore fluids trapped within the clays' microporosity.