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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 4. (April)

First Page: 671

Last Page: 671

Title: Electrofacies Identification of Lithology and Stratigraphic Trap, Southeast Lost Hills Fractured Shale Pool, Kern County, California: ABSTRACT

Author(s): M. E. Mulhern, J. E. Laing, J. E. Senecal, R. E. Widdicombe, C. Isselhardt, J. R. Bowersox

Article Type: Meeting abstract


Subtle facies changes are traced vertically and laterally in the upper Monterey and Reef Ridge formations through application of the Multi-well Faciolog (mark of Schlumberger) technique. Electrofacies, representing intervals of similar log response, are identified in a key well by comparison with mud-log, conventional core, and x-ray Previous HitdiffractionNext Hit analysis Previous HitfromNext Hit sidewall cores and are retained in a data base. Five subsequent wells lacking detailed core or x-ray data but with similar log suites (bulk density, neutron porosity, gamma ray, and delta time) were compared to the data base and automatically assigned electrofacies. Twelve electrofacies--including diatomite, porcellanite, chert, dolomite, mudstone, and claystone, plus intermediate members--have been identified at the depth accuracy and resolution of petrophysical logs.

The lateral updip diagenetic facies changes Previous HitfromNext Hit porous, hydrocarbon-productive diatomaceous mudstone to impermeable, low-porosity, non-productive porcellanite are clearly illustrated by the Faciolog cross-sectional display. McGuire et al, documenting the change Previous HitfromNext Hit mudstone to porcellanite, recognize it as a controlling factor in formation of a stratigraphic trap. Vertical electrofacies associations reflect cyclic paleoclimatic trends and provide sedimentary sequences that aid in well-to-well correlation, field studies, and mapping in otherwise nondescript shales. Lithologic characterization of fine-grained, compositionally variable reservoirs, such as the Monterey Formation and equivalent rocks, is critical in understanding diagenetically altered porosity and, therefore, production

Comparison of average log values for each electrofacies with equivalent Miocene-age coastal basin rocks reveals decreased dolomite and increased terrigenous clay content in the Lost Hills strata. Using the Faciolog technique, combined with x-ray Previous HitdiffractionTop analysis, allows identification of average log values associated with specific lithologies.

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Copyright 1997 American Association of Petroleum Geologists