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S.J. Mazzullo1
(1) Wichita St. Univ, Wichita, KS

Abstract: Porosity evolution in Permian deep-water carbonates, Permian Basin, Texas & New Mexico

Hydrocarbon reservoirs in lower Permian, resedimented periplatform carbonates in the Midland and Delaware basins are mainly in megabreccias and finer-grained carbonate-clast conglomerates (debris-flows) and carbonate sands (gravity-flow deposits). Reservoirs in the former typically are thick, lenticular to channelized bodies, oriented parallel or normal to platform margin sources, with matrices of carbonate mud to gravelly sand. Reservoirs in gravity-flow deposits are thinner, lenticular bodies oriented normal to platform margins. Porosity occurs in both limestone and dolomite. Inherited meteoric porosity within clasts, and interparticle porosity in the carbonate sands and conglomerates, were occluded after redeposition into the deep (1500-1800 ft) basin by compaction and cementation accompanying progressive burial. Oxygen isotope data suggest that dolomitization of some of these deposits began soon after redeposition and continued into the intermediate-depth burial environment, but this process did not create secondary porosity. Petrographic, oxygen isotope, and vitrinite reflectance data suggest that secondary dissolution porosity in the limestones and dolomites developed concurrently with hydrocarbon maturation in enclosing shale source rocks. Pore types mimic those commonly formed in subaerial meteoric environments. Estimation of onset of hydrocarbon generation suggests that most porosity formed during the Mesozoic as a consequence of interaction with undersaturated fluids evolved during hydrocarbon maturation. Modeling of paleofluid-flow may assist in predicting potential-porosity “fairways” in the subsurface.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana