--> Abstract: Did Dolomitization Create Porosity in the Miocene Carbonates of the Middle East?, by S. Q. Sun and M. Esteban; #90987 (1993).

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SUN, S. QING, and MATEU ESTEBAN, ERICO Petroleum Information Ltd., London, UK

ABSTRACT: Did Dolomitization Create Porosity in the Miocene Carbonates of the Middle East?

Miocene carbonate, an important hydrocarbon-producing reservoir in the Gulf of Suez and Middle East, was deposited in arid, land-locked, subtropical/temperate settings. Fluctuations in relative sea level produced marked cyclicity of carbonates-evaporites at different orders of magnitude.

Dolomitization occurs extensively on the Miocene carbonates throughout the region and is believed to have been caused by hypersaline brines. The most striking diagenetic feature associated with dolomitization is the widespread dissolution of skeletal aragonite with little or no calcite cementation. Petrographic data indicate that there was no increase in porosity after dolomitization. Processes of dolomitization at best preserved original porosity or transformed porosity from one form to another. Skeletal aragonite was extensively leached by hypersaline brines, while the micrite matrix and micritized grains experienced pervasive dolomitization. The dissolved calcium carbonates were incorporated into the nearby micrite matrix, forming additional dolomites. Consequently, large volumes o moldic and vuggy porosity were created, whereas originally porous micrite matrix was replaced by relatively tight, finely crystalline dolomite. Intercrystalline porosity only occurs in areas with limited quantity of skeletal aragonite. However, under shallow burial conditions, significant volumes of moldic and vuggy porosity were occluded by anhydrite cements. With continued burial and during hydrocarbon emplacement, the porosity of these dolomites was restored to 20-30% through fracturing and late corrosion of anhydrite cements, micritized grains and matrix.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.