Sequence stratigraphy of the upper San Andres and Grayburg formations, Waddell Field, Crane County, Texas: implications for hydrocarbon reservoir distribution

Abstract

The upper San Andres and Grayburg formations (Guadalupian) were deposited on carbonate platforms around the Permian Basin region and are extensive hydrocarbon reservoirs in the region. The Waddell Field (East Waddell Ranch) on the eastern margin of the Central Basin Platform has been producing hydrocarbons since 1935 and current engineering activity includes infill drilling and varying enhanced recovery strategies. This study establishes a sequence stratigraphic framework for the upper San Andres and Grayburg formations-nations in the Waddell Field using cores, well logs, and outcrop analogs. The sequence stratigraphic interpretation was correlated to equivalent. strata on the Northwest Shelf and compared to known reservoir horizons in the Waddell Field. On the western margin of the field, production is dominant in deep to shallow subtidal lithofacies in two high-frequency sequences. These two high-frequency sequences correspond to Guadalupian 12 and 13 high-frequency sequences described on the Northwest Shelf. The San Andres and Grayburg formations are separated by a Type I sequence boundary during which subaerial exposure of the platform and siliciclastic progradation occurred. Production from the Grayburg Formation is also dominated by subtidal peloidal facies and migrates towards the eastern margin of the field, higher in the stratigraphy. The Grayburg sequence model divides the formation into two highfrequency cycles which correspond to Guadalupian 14 and 15 high-frequency cycles on the Northwest Shelf based on sequence geometry, platform position and high-frequency cycle type. Reservoirs in the Waddell Field (East Waddell Ranch) produce almost exclusively from the deep to shallow subtidal facies in the transgressive systems tracts of each high-frequency sequence and only down-dip from the inter-and supratidal facies. Up-dip shallow and peritidal facies within the transgressive systems tracts and in the overlying high-stand systems tracts provide up-dip and overlying seals.