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Abstract: Lithofacies Distribution and Reservoir Characterization of Pennsylvanian Phylloid Algal Mounds, Western Orogrande Basin, New Mexico

DOHERTY, PATRICK D., University of Oklahoma, Dept. of Geology & Geophysics, Norman, OK

Phylloid algal mounds form significant reservoirs within the Paradox and Permian basins and house million to billion barrel fields. Understanding the distribution of lithofacies and porosity-permeability trends is integral to efficient hydrocarbon recovery from these potentially heterogeneous reservoirs. The primary objective of this project is to characterize the lithofacies and construct a high frequency sequence stratigraphic framework, which will be used to build a 3D reservoir flow model.

Upper Pennsylvanian (Virgilian) phylloid algal mounds are exposed in the western Orogrande basin (San Andres Mountains), but remain understudied owing to their location on the White Sands Missile Range. Preliminary analysis suggests that these mounds consist of a series of mound growth events punctuated by exposure surfaces. These surfaces are marked by pronounced dolomitization and associated porosity enhancement.

To accomplish my objectives I will: 1) measure 15 to 20 closely spaced sections through the mound core and its flanking strata, 2) sample for porosity-permeability analysis and petrography, 3) identify lithofacies and subaerial exposure surfaces, 4) correlate surfaces between sections via physical tracing and photomosaics, 5) use the field data to build a high frequency cyclostratigraphic framework, and 6) apply this data to formulate a three dimensional reservoir flow model.

I will target one of the large (>100m stratigraphic thickness) mounds exposed in Hembrillo canyon (San Andres mountains). This outcrop is extremely well exposed in three dimensions, and should yield excellent data for constraining a reservoir model. Because this outcrop is of reservoir scale it should serve as a realistic model for productive subsurface analogs in the Permian and Paradox basins and ultimately aid in their exploitation.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid