Editor’s Note

The Upper Arab-D, or Zone-1 reservoir represents a significant but little produced interval within the larger Arab-D reservoir at Abqaiq Field. The Arab-D is divided into 3 main reservoir zones with Zones-2 and 3 contributing most of the oil production. The Upper Arab-D is less than 30 feet thick, consists of a basal low-porosity dolomite to dolomitic limestone, a medial high energy skeletal-peloidal grainstone/ packstone reservoir facies, and an upper unit of interbedded dolomudstones, cryptalgalaminates and nodular-to-bedded anhydrites that generally grades upwards into massive anhydrite. Open hole logs indicate high oil saturations, but flow meters reveal little to no contribution from Zone-1, regardless of completion type in vertical wells. This necessitates development of Zone-1 via long-radius (>1,000 feet lateral section) and short radius (<1,000 feet) horizontal wells to deplete recoverable oil, and to avoid contribution of water from Zone-2. Successful development of the Upper Arab-D requires detailed characterization, correlation and mapping of the basal dolomite unit, containing very thin (1 to 2 feet) impermeable beds within it. These beds are important in preventing cross-flow of water from Zone-2, but are beyond the resolution level of open-hole logs. Porosity-permeability transforms from core analysis data coupled with petrographic data have enhanced the ability to predict and map the impermeable beds in non-cored wells. Porosity and permeability maps based on minimum cut-off porosity values, and aerial distribution of the basal dolomite unit are providing the necessary geologic control for horizontal well placement. This will optimize depletion of recoverable hydrocarbon, using both long-and short-radius horizontal drilling technology, from the Upper Arab-D reservoir at Abqaiq Field.