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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 301

Last Page: 301

Title: Recognition of Previous HitAnhydriteNext Hit Dissolution--A Cause of Secondary Porosity in Two Petroleum Reservoirs: ABSTRACT

Author(s): Randall W. Richardson, Christopher J. Schenk

Article Type: Meeting abstract


Rectangular and "stair-step" pore reentrants in carbonate mudstones have been recognized previously as indirect evidence for Previous HitanhydriteNext Hit dissolution. In this study, direct evidence for dissolution of interstitial Previous HitanhydriteNext Hit in subsurface rocks includes: (1) cleavage-related dissolution fringe on Previous HitanhydriteNext Hit crystal surfaces and (2) isolated remnants of optically continuous (formerly poikilotopic) Previous HitanhydriteNext Hit. Influenced by the prominent cleavages, the dissolution fringe on the surfaces of the Previous HitanhydriteNext Hit crystals consists of a series of sharp, right-angled projections and reentrants. Experimentally etched Previous HitanhydriteNext Hit surfaces exhibit features that directly compare to the dissolution fringe, whereas experimentally grown Previous HitanhydriteNext Hit does not.

Previous HitAnhydriteNext Hit in both the dolomite grainstones of the Permian San Andres Limestone in the Vacuum field, Lea County, New Mexico, and the sandstones of the upper (Permian) part of the Minnelusa Formation in the West Mellot Ranch field, Crook County, Wyoming, exhibited these direct evidences, demonstrating the presence of secondary porosity after Previous HitanhydriteNext Hit.

We deduced the following sequence of Previous HitanhydriteNext Hit dissolution within these rocks. Slow incipient dissolution began along the boundaries between Previous HitanhydriteNext Hit and adjacent minerals. From these intercrystalline boundaries, solutions penetrated Previous HitanhydriteNext Hit cleavages, leading to more rapid preferential dissolution perpendicular to the more prominent cleavage planes. The widened cleavage planes, together with intercrystalline boundaries, acted as conduits for removal of dissolved ions. In the final stage, as dissolving Previous HitanhydriteTop borders retreated toward pore throats, dissolution slowed and was, again, restricted to intercrystalline boundaries. This process was repeated in adjacent interstices.

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