--> Abstract: Mass Transfer and Water-Oil-Mineral Interaction: Implications from Calcite Cements of the San Joaquin Basin, California, by J. R. Boles; #90928 (1999).

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BOLES, JAMES R.
Department of Geological Sciences, University of California, Santa Barbara, California, 93106

Abstract: Mass Transfer and Water-Oil-Mineral Interaction: Implications from Calcite Cements of the San Joaquin Basin, California

Calcite cements formed in relatively open systems at intermediate burial depths in the central San Joaquin basin. Cements typically have lower 87/86Sr than the depositional marine water, have progressively lower ratios with increasing temperature of crystallization and are sourced from alteration of plagioclase. These cements have carbon isotopic composition sourced in part from thermogenic-derived carbon and in some cases show marked fluctuation in carbon isotopic values, which has been interpreted as evidence for pulses of deep-basin fluid mixing with fluids at shallow levels. Upward and outward movement of basin fluid is also implied from the early arrival of low 87/86Sr fluids in reservoirs closest to the deep basin.

During deep burial, calcite cements have formed in relatively-closed systems with components being derived from reactions within the reservoir. Carbon isotopic values of cements are, in many cases, near zero (PDB). Low strontium isotopic values in cements imply that that dissolution of shell tests is not a primary source of calcium or carbon. Late cements appear to have formed in a relatively closed system, with cement components being derived locally from within the reservoir as a result of the presence of the hydrocarbons and plagioclase. Carbon may be indirectly sourced from organic acids in the formation waters which are derived from oils in the reservoir. Recent studies suggest organic acids may have carbon isotopic compositions near zero, similar to that in the cements.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas