Aspects of Permian Paleowind Directions in the Unayzah-A Reservoir, Subsurface Eastern Central Saudi Arabia, Utilizing Integrated Core and Image Log Data

The Lower Permian Unayzah-A reservoir unit in the subsurface of eastern central Saudi Arabia displays widespread evidence of deposition under arid to semi-arid conditions, very commonly in a wind-dominated, aeolian setting. A number of distinctive aeolian depositional facies are recognized from core and image logs including: dunes, interdunes, sand sheet, and playa lakes. They occur with a high degree of repeatability throughout the Unayzah-A reservoirs. The study investigated the distribution of azimuthal variability in Permian paleowind data across the Kingdom. The data were derived from image log patterns throughout the aeolian dune facies identified in the subsurface Unayzah-A reservoir unit from within four fields selected for this study. The study involved sedimentological description of 1160 feet of core data from six wells and analysis of 4000 feet of image log data from twenty-one wells, which spanned the area from central to eastern Saudi Arabia. A hierarchical approach was employed to investigate the paleowind directions as follows: Paleowind azimuthal data were i) recorded appropriately for each identifiable bed; ii) averaged over each bedset within each well; iii) averaged over each well; iv) averaged over each field; v) and finally averaged over the four studied fields. This rigorous approach resulted in the identification of a dominant paleowind direction toward east-northeast direction (present day), with a window ranging between 40 and 100 degrees and a mean vector of 72 degrees. Identifying the dominant paleowind direction provides an understanding of dune distribution and shape throughout the reservoir. It also facilitates a hydrocarbon development program that can optimize exploitation of porosity and permeability distributions.