الملخص الإنجليزي
Gharif Formation is one of the most important hydrocarbon reservoirs in Sultanate of Oman. This study presents a petrophysical analysis and 3D geological (static) model carried out to evaluate the rock properties, reservoir quality and hydrocarbon potentiality of the Gharif Formation in Sahmah Field which consists of four different reservoirs units namely (Upper Haushi Sand (UHS), Dolomite Drain (DD), Sandstone Drain (SD) and Lower Haushi Sand (LHS)).Conventional wireline logs collected from 32 wells were used to identify lithology, shale volume, porosity, fluids saturation, fluid contacts and permeability of reservoir intervals from the studied field. Lithologically, UHS and SD are interpreted to be composed of dolomitic sandstone interbedded with calcareous shale, DD consists of sandy dolomite and dolomitic limestone, while LHS is composed of homogeneous sandstone in east and southeast to dolomitic sandstone in west and northwest of the field. The portion of quartz (sand) in all reservoir units decreases from eastern and southeastern part toward the western and northwestern parts of Sahmah Field. On the contrary, the dolomite and calcite portions obviously decrease in the opposite direction. These trends follow the transition from more proximal setting (alluvial plain) in the southeast to basinal setting (marginal marine) in the northwest.Based on the variations of petrophysical properties and fluid saturation, the Gharif Formation is not homogeneous. Petrophysical properties vary significantly in various directions. LHS (upper drain and lower drain) demonstrates sharp change of fluid saturation from north with oil to south with water. On the contrary, UHS is water saturated to the north and oil-saturated to the south. DD is mostly oil saturated, whereas SD is mostly water saturated because it is located below OWC.Effective porosity values of LHS increase in the northern part of the field and decrease to the southern part from poor to fair porosity for upper drain and from good to very good porosity for lower drain. SD shows increasing trend of effective porosity when moving from the southeastern part of the field toward the northwestern part from poor to good porosity. Reversely to SD, UHS shows increasing trend of effective porosity when moving from the northwestern part of the field toward the southeastern part from poor to good porosity. Effective porosity of DD grades from poor to good porosity with lowest value in the central part of the field. Permeability gradually increases from shallower depth (UHS) to deeper depth (LHS), from (poor and fair permeability) to (good and very good permeability).In conclusion, integration of all petrophysical analysis data led to building of a consistent 3D geological model (which considers both structure and property) of the reservoir which can be used as input into a reservoir simulation model and provides a basis for a very effective reservoir management strategy. The total number of 3D grid cells came up to (1680672), being enough to capture all the details of the reservoir. The petrophysical properties are distributed stochastically within a 3D grid using Sequential Gaussian Simulation. The volumetric calculations indicate that the total volume of oil in place is 46×10,6 m3.
