HORTON, R. A., JR., P. T. MCCULLOUGH, B. D. HOUGHTON, and J. A. DUNWOODY III, Department of Geology, California State University, Bakersfield, CA

ABSTRACT: Dissolution, Compaction, and Destruction of Secondary Porosity in Reservoir Sandstones in the San Joaquin Basin, California

Miocene reservoir sandstones in many central San Joaquin basin oil fields (Coalinga, Elk Hills, Jacalitos, Kettleman City, Midway-Sunset, South Belridge, Tulare Lake) consist of arkosic and lithic arenites derived from granitic and volcanic source areas to the west and deposited in diverse depositional environments in a tectonically active basin. Each of the fields studied shows a similar history of porosity development. Initial compaction accompanied by alteration and squashing of volcanic grains resulted in near total destruction of primary porosity. This was followed by extensive leaching of framework grains resulting in shifts in QFL ratios; however, precipitation of authigenic pore-filling clays was rare. Continuing compaction altered the geometry of the secondary pores to create intergranular secondary porosity which mimics primary intergranular porosity. Although difficult to quantify, collapsed clay rims and rearrangement of grain fragments indicate substantial destruction of secondary porosity. These features are best developed along the western margin of the basin where tectonic as well as burial compaction resulted in extensive crushing of grains and influxes of meteoric water resulted in significant grain dissolution, particularly along fractures; as much as 80% of the intergranular porosity in these sands is secondary. These observations suggest that secondary porosity may be more widespread than is generally recognized.

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