--> Abstract: Porosity Evolution in Reservoir Sandstones in the West-Central San Joaquin Basin, California, by R. A. Horton, Jr., P. T. Mccullough, B. D. Houghton, D. A. Pennell, J. A. Dunwoody III, and R. J. Menzie, Jr.; #90958 (1995).

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Abstract: Porosity Evolution in Reservoir Sandstones in the West-Central San Joaquin Basin, California

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

Miocene reservoir sands (feldspathic and lithic arenites) in central San Joaquin basin oil fields show similar trends in porosity development despite differences in depositional environment, pore-fluid chemistry, and burial history. Burial and tectonic compaction caused grain rotation, deformation of altered lithics, and extensive fracturing of brittle grains, thereby eliminating most primary porosity. Diagenetic fluids, infiltrating along fractures in grains, reacted with freshly exposed mineral surfaces causing extensive leaching of framework components. All major grain types were affected but preferential removal of feldspars and lithics resulted in changes in QFL ratios. With continued compaction angular remnants of partially dissolved grains were rotated and rearrang d while secondary intragranular and moldic porosity collapsed to form secondary intergranular porosity. This resulted in reservoir sands that are less well sorted, more angular, and mineralogically more mature than they were at deposition. Such changes appear to widespread in the San Joaquin basin and may be more important than is generally acknowledged.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California