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Preliminary Study Of The Mineralogy And Diagenetic History Of The Temblor Formation Sandstones, 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 from two wells were obtained from the California Well Sample Repository. Depths range between 2403 and 3044 meters. These were studied using petrography and scanning electron microscopy-energy dispersive spectrography (SEM-EDS). The Temblor sandstones consists of fine to very coarse poorly to well sorted arkosic arenites. The detrital framework grains include sub-angular quartz, K-feldspar (microcline and orthoclase), plagioclase and rock fragments. Accessory minerals include glauconite, biotite, muscovite, magnetite, titanomagnetite, sphene, zircon, and apatite. Three chemically distinct types of K-feldspars have been identified, Ba-free, Ba-rich, and perthite. Diagenetic alteration includes compaction, dissolution of detrital minerals, albitization of feldspars, cementation by kaolinite, calcite and dolomite, replacement of framework grains by calcite, alteration of volcanic rock fragments and the alteration of biotite to pyrite and chlorite. Pyrite formed following petroleum migration. 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. 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 and K-feldspars.