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

R. A. Horton Jr., P. T. MCCullough, B. D. Houghton, D. A. Pennell, J. A. Dunwoody, III

Feldspathic and lithic arenites of Miocene age in central San Joaquin basin reservoirs show similar trends in porosity development despite differences in depositional environment, pore-fluid chemistry, or burial history. Initial compaction resulted in destruction of most primary porosity through grain rotation and deformation of altered lithics. Continued burial and tectonic compaction resulted in extensive fracturing of framework grains thereby exposing fresh surfaces to diagenetic fluids. Extensive leaching of framework components, including fractured quartz grains, followed, with preferential removal of feldspars and lithics causing changes in QFL ratios. With continued compaction, angular remnants of partially dissolved grains were rotated and rearranged while secondary intragranu ar and moldic porosity collapsed to form secondary intergranular porosity. The resultant reservoir sands are less well sorted, more angular, and mineralogically more mature they were at deposition. These processes have occurred in all fields studied to date suggesting that grain dissolution, leading to mineralogical and textural changes and the formation of secondary porosity, may be more important than is generally acknowledged.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994