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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 1. (January)

First Page: 141

Last Page: 142

Title: Free Convection in Gulf Coast Reservoirs: ABSTRACT

Author(s): Paul E. Blanchard, John M. Sharp, Jr.

Article Type: Meeting abstract

Abstract:

Several observed diagenetic changes in Gulf Coast sediments, such as dissolution of calcite and feldspar and pore cementation by silica and calcite,

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require many changes of pore fluid. The number of pore volumes required is much greater than can be derived from compaction alone. Free convection, if it exists, is an attractive process in accounting for these observations. Three lines of evidence indicate that free convection is occurring in at least some Gulf Coast reservoirs. First, Rayleigh-Darcy calculations were made for a variety of reservoir thicknesses, permeabilities, and thermal gradients. Reasonable Gulf Coast values were selected and thermally sensitive parameters were allowed to vary with temperature. Critical Rayleigh numbers were exceeded for thick Gulf Coast sands. Depending on site-specific conditions, diagenetic reduction of permeability may create a preferred depth range for the occurrence of free convection. The econd line of evidence includes pore-fluid density, silica content, and temperature data for Frio Formation waters. These data are consistent with a freely convecting system. Third, areal distribution of thermal gradients within a Frio reservoir exhibits a geometric pattern completely consistent with Benard-type convection cells: central, upward-moving, heated plumes surrounded by polygonal zones of cooler, down-flowing waters. Therefore, free convection in Gulf Coast reservoirs is consistent with both field data (as demonstrated in the Frio Formation) and theoretical calculations.

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