--> ABSTRACT: Facies Architecture of Ooid Grainstone-Dominated Cycles In a Sequence Stratigraphic Framework: Grayburg Formation, New Mexico, by R. J. Barnaby and W. B. Ward; #91021 (2010)

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Facies Architecture of Ooid Grainstone-Dominated Cycles In a Sequence Stratigraphic Framework: Grayburg Formation, New Mexico

BARNABY, ROGER J., and W. BRUCE WARD

The Grayburg (middle Guadalupian) is a major producing formation in the Permian Basin of West Texas and southeastern New Mexico. Producing fields flanking the Delaware and Midland Basins generally have yielded less than 30 percent of their original oil in place and are undergoing secondary and tertiary recovery. Efficient design of these enhanced recovery programs dictates improved stratigraphic models to assess reservoir heterogeneity imposed by depositional and diagenetic controls.

Grayburg outcrop exposures in the Brokeoff Mountains region (Northwest Shelf, Delaware Basin) provided a rare opportunity to construct a detailed, three-dimensional image of reservoir-scale facies architecture in order to better understand and predict depositional heterogeneity in analogous subsurface reservoirs. The Grayburg Formation consists of four high-frequency sequences (HFS 1-4) that are 100 to 160 ft thick. Each HFS is composed of multiple upward-shoaling cycles (3--30 ft thick) arranged into well- defined transgressive and highstand systems tracts. Grayburg HFS 2 contains ooid grainstone-dominated cycles that accumulated under transgressive and highstand conditions. Stratigraphic analysis of this interval documents the influence of the stratigraphic position on the three-dimensional distribution and heterogeneity of permeable ooid grainstone bodies from different cycle settings.

Grainstone bodies in the transgressive systems tract exhibit considerable lateral discontinuity (tens to hundreds of feet) and formed dip-elongate channels and bars. This heterogeneous facies distribution reflects a tide-dominated setting during transgression, accompanied by rapid increase in accommodation that resulted in high preservation potential of individual facies bodies. Highstand ooid grainstones formed strike-elongate shoals that are laterally continuous along dip and across strike (hundreds to thousands of feet) and record amalgamation of stacked grainstone bodies in an accommodation-limited highstand setting. This relationship between stratigraphic position and facies heterogeneity can be utilized to better constrain and predict the distribution and dimensions of permeable facies at the reservoir and interwell scale. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.