McCULLOUGH, PATRICK T., and ROBERT A. HORTON, JR., Department of Physics and Geology, California State University, Bakersfield, CA

ABSTRACT: Diagenesis and Porosity Development in Temblor Formation Sandstones at Tulare Lake Field, San Joaquin Basin, California

Tulare Lake field lies in the central portion of the San Joaquin basin with Temblor Formation sandstones (late Oligocene and early Miocene) at depths of 3200 to 4100 m. Arkosic arenites and feldspathic graywackes have undergone diagenetic modifications of the original rock fabric significantly altering reservoir quality. Minor fracturing of grains due to compaction suggests that early carbonate cement filled interstitial pore spaces, limiting the effects of compaction. Oversized pores and ghosts of grains indicate that dissolution of unstable grains and carbonate cement resulted in generation of significant secondary porosity. Although all framework grains show signs of dissolution, plagioclase and volcanics were particularly susceptible.

Recognition of secondary porosity is extremely important in this area as it represents approximately 50% of the total porosity. Porosity in these deep Temblor sands varies from 0 to 25% with no correlative relationship to depth. Although minor amounts of authigenic quartz cement and clay are present, the amount of framework grain dissolution far exceeds authigenic precipitation. Albitization of plagioclase and K-feldspar grains has also occurred, resulting in additional mobilization of aluminum. All evidence indicates mass transfer of material out of the system resulting in an enhancement of porosity due to diagenetic modifications.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.