--> Abstract: Contrasting Artificial (Steam-induced) Diagenesis at Kern River and Midway-Sunset Oil Fields, California, by D. A. Pennell and R. A. Horton, Jr.; #90935 (1998).

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Abstract: Contrasting Artificial (Steam-induced) Diagenesis at Kern River and Midway-Sunset Oil Fields, California

PENNELL, DAWNE A., and ROBERT A. HORTON, JR., Department of Geology, California State University, Bakersfield, California 93311

The Potter sand (Upper Miocene) in the Midway-Sunset field consists of lithic (volcanic) arenites derived from source areas to the west. The Kern River Formation (Pliocene-Pleistocene) in the Kern River field is primarily arkosic arenite derived from the Sierra Nevada to the east.

At Kern River field changes observed between pre- and post- steam samples are minor and include: 1) dissolution of framework and accessory grains, 2) slight increase in illite/smectite and slight decrease in kaolinite, 3) increased alteration of feldspars and pseudomatrix, 4) precipitation of small amounts of calcite.

At Midway-Sunset a number of significant changes were observed in post-steam samples: 1) dramatic increase in grain dissolution which altered the QFL ratios, 2) dissolution of sulfates, 3) disappearance of chlorite, 4) formation of smectite, 5) increase in ordering and illite content of mixed illite/smectite, 6) alteration of biotite accompanied by precipitation of calcite and pyrite, 7) increased alteration of framework grains and pseudomatrix, 8) decrease in average porosity from 25.4% to 19.7%, 9) formation of clay bridges and pore-filling cements.

Steam injection caused major changes at Midway-Sunset but only very minor changes at Kern River. The most significant difference between these two reservoirs is the composition of the sands. The most dramatic changes observed at Midway- Sunset occurred among clay minerals which mainly were derived from alteration (both natural and artificial) of volcanics. The decrease in porosity and changes in pore morphology have the potential to eventually effect production.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California