A preliminary rock typing scheme for the Upper Jurassic was established on Arab reservoirs on a field offshore Abu Dhabi. This study was performed in order to assist in the reservoir modeling and ultimately in the accelerated development scheme of the field. The study is based on 165 samples from all the Arab reservoir levels (Arab A, B, C, D) in 6 wells. These samples were selected to cover all the reservoir facies and the range of porosity and permeability. All these samples have MICP data, thin section and porosity/permeability data. The objective was to identify the major rock types occurring in the Arab reservoirs from these samples.Rock types of the Arab Formation can be divided into 3 major rock type groups: Limestone, Dolomite, and Anhydrite. Limestones predominantly occur in the Arab D reservoirs, the dolomites in the Arab A, B, and C. Anhydrite occurs as non-reservoir, intraformational seal, and/or baffle between Arab, A, B, and C or is intercalated in these reservoirs.Six rock types were identified in the limestone reservoirs (L1 to L6) and five rock types were identified in the dolomite reservoirs (D1-D5). Various degree of overlap in reservoir properties do exist between some of these sub-groups. The dolomite rock types are easier to be classified into rock types compared to the limestone because of their uni-modal pore throat size distribution and well-defined capillary pressure curves. Reservoir quality is related to crystal shape, size, crystal-to-crystal contact, and dissolution.Limestones are much more complex and reservoir quality is controlled by mud content, grain size, sorting and diagenesis. Dissolution creating vuggy porosity can create high perm zones if the vugs are connected in both dolomites and limestones. Three limestone rock types show a pronounced dual-porosity system which is difficult to characterize with conventional rock typing methods.This work is being used to assist in the detailed characterization of the offshore field and in the ongoing field development.

A study has been initiated to determine the best development scheme to recover oil and gas from two oil rim reservoirs off shore Abu Dhabi utilizing horizontal wells. One pilot horizontal well has already been drilled in the lower reservoir and few more are planned. Due to uncertainties in the fluid contacts and reservoir characteristics, a vertical pilot hole had to be drilled and cored to decide on the optimum location of the horizontal hole. A detailed core study was conducted to study the main rock types and lithofacies of this reservoir and a sector model was constructed to study the effect of different reservoir parameters on the performance of the horizontal well. PVT data from the gas cap and the oil rim will be used to construct an EOS that will be used in the full field compositional model. The results from this model and the performance of the pilot horizontal wells along with ongoing detailed geological study will help in determining the optimum development plan for these reservoirs.