Modeling a Rich Gas Condensate Reservoir with Composition Grading and Faults

Abstract

Abstract The Hawiyah Jauf Reservoir is a complex structural-stratigraphic trap located along the east flank of the uplifted Ghawar structure. The two important aspects of this reservoir are fieldwide composition variation and reservoir compartmentalization. The reservoir fluid samples obtained during developmental drilling show remarkable differences in fluid properties and condensate yields. The condensate yield of collected samples varies form more than 250 STB/MMscf to less than 100 STB/MMscf, and the reservoir fluid at the gas-water contact exhibits the near-critical behavior. Furthermore, the complicated fault system subdivides reservoir into several major compartments. In order to model the fieldwide composition variation, all fluid samples must be characterized reasonably well by using one equation of state (EOS) fluid model. An eight-component EOS fluid model has been generated based on four fluid samples. A geological model was built to honor the faults that were interpreted from the recent 3D seismic survey. A series of prediction runs are planned to forecast the reservoir behavior and hydrocarbon recoveries under various operational scenarios including simple depletion as well as cycling at different stages of production. Sensitivity runs are also made to investigate the impact of uncertainties associated with geologic and reservoir properties. Introduction As part of the effort to satisfy the Kingdom's increasing demand in gas as fuel and feedstock, Saudi Aramco has accelerated the development of many recently discovered gas reservoirs. At present, the primary gas production comes from the prolific Khuff carbonate formation that underlies the major oil production zone - Arab-D. The deeper Jauf (pre-Khuff) Formation was found also containing a significant amount of gas reserve and more importantly, the gas in this formation is sweet. The Jauf Reservoir is present throughout the eastern region of Saudi Arabia, but this paper is focused on the development of the Jauf Reservoir in Hawiyah area of the Ghawar field. A massive program has been launched to bring the Hawiyah Jauf Reservoir to production by September 2001 and reservoir simulation is one of the major tools that are being used to address many issues related to the field development and production optimization. The Jauf Formation is early Devonian sandstone. It consists of shallow marine sands deposited over a broad shelf. The formation includes fine to medium grained sandstone and the hydrocarbon traps are found in simple four-way closures as well as more complex structural-stratigraphic traps. The primary source rock for the Jauf Reservoir is the basal hot shale of the Lower Silurian Qalibah Formation. The 3D seismic survey reveals that the reservoir is highly faulted, especially in the southwestern part of the field. The compartmentalization resulted from the fault system has significantly increased the complexity of the field development. The field is gradually pinched out toward the west and bounded by major faults at both west and east. The reservoir fluid samples collected during the developmental drilling show a high degree of variability in gas composition as well as condensate yields. PVT analysis indicates that the Hawiyah Jauf Formation is a rich gas condensate reservoir and part of reservoir fluid exhibits the near-critical behavior. The main objective of this study is to address the field development issues and to optimize the future hydrocarbon production using a state-of-art compositional simulation model. In order to use this model confidently in forecasting the field performance, the model must include all important aspects specific to the Hawiyah Jauf Reservoir.