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Cretaceous Giant Siliciclastic Reservoirs Depositional Models in Kuwait


The most important Cretaceous siliciclastic reservoirs in Kuwait are Zubair, Burgan, Mauddud and Wara formations. They are productive in many fields such as Burgan, Ahmadi, Maqwa, Raudhatain, Sabriyah, Bahrah, Minagish, Ratqa, Abdali, Khafji and Dorra fields. Zubair Formation consists of alternating sandstone, siltstone and shales and minor limestone, representing littoral and partly deltaic, estuaries to marine sedimentation. It has multiple reservoirs which occur in well-developed sand horizons, with porosity of 14-24%, permeability between 400-4000md and oil gravity ranging from 35-38 API. Burgan Formation is divided into two members. The Upper Sandstone Member consists of interbedded glauconitic sand and dark grey shale with middle unit of quartz sand. This reservoir has porosities 12-20% and permeabilities 380-600md, with oil gravity of 28-36 API. The Lower Sandstone Member consists of shale, medium to coarse-grained, well sorted quartz sandstone. The reservoir has more than 400md permeability and an average of 23% porosity, and oil gravity 29-32 API. These clastics were deposited in tidal-influenced, coastal-marine transitional graded into fluvial-dominated and continental setting. Mauddud Formation is characterized by siliciclastic and carbonates facies. The carbonate were deposited in moderate to high energy, upper ramp setting of moderate energy, and upper-middle ramp to deeper lagoonal setting. The siliciclastic of deltaic origin composed of medium to fine-grained glauconitic sandstones, bioturbated mud rich sandstone and dark shale. The formation has low porosity and permeability with oil gravity of 27-30 API. The porosity in the sandstones and the dark shales ranges between 5 to 12%, while the permeability is 0.3-11 md. Wara Formation comprises multi-storey fluvial/ tide-influnced deposits within incised valley, consists of predominantly shaley sequence with thin sandstone layers in the lower part, graded upward to complex interbedded sequence of argillaceous laminated and bioturbated and glauconitic sandstones and shales. A prominent flooding surface separates the lower Wara from upper Wara, which comprises tide-influenced proximal delta-front and delta-top deposits. The reservoir has a 29-36 API oil gravity, 30-35% porosity, and permeabilities up to 3000 md.