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Summary This paper describes the application of compositional reservoir simulation techniques in the management of large reservoirs. The equation-of-state compositional simulator was specifically enhanced to address several technical challenges, such as geologic heterogeneities including crossing faults and widely varying permeability, complex phase behavior of a near-critical fluid, and involved surface facilities operational constraints. In the study we utilize sophisticated well-management schemes to evaluate and optimize condensate production under various development strategies and surface facilities constraints. The application of the simulator to the Oso field in Nigeria is presented. The Oso field has two reservoirs. This field study reports on the major reservoir which contains a near-critical fluid and has a highly faulted structure. The fault model, in addition to accurately representing geologic faults and the associated flow across different layers, also reduced computational requirements considerably over the old conventional methods for fault representation. The reservoir fluid and its behavior near the critical region was characterized accurately using an 8-component, equation-of-state model. The application of the model in the study of reservoir recovery under various production scenarios is discussed. The displacement mechanisms involved in the different depletion strategies are explained through a series of 1-dimensional simulations. This integrated approach in reservoir management enables us to determine an optimal development plan and surface facilities design parameters for the Oso reservoir. Introduction The Oso field, discovered in 1967 with the drilling of several appraisal wells, is located approximately 35 miles offshore southwestern Nigeria and is owned 60% by the Nigerian National Petroleum Corporation (NNPC) and 40% by Mobil Producing Nigeria Ultd. (MPNU). MPNU is also the operator of the field. The Oso field has two reservoirs, 1-Y1 and 2-Y2, separated by large shale barriers. The reservoir temperature is 232F at a depth of 10,000 ft and is slightly overpressured. In this simulation study we report on the 1-Y1 reservoir which is the major reservoir in the Oso field. It has a highly faulted structure with significant shale barriers and large contrast in the absolute permeability variations. The 1-Y1 reservoir fluid exhibits a near-critical behavior. The development of the Oso field is currently underway and requires the construction of several offshore platforms, a condensate pipeline from the field to the terminal, storage tanks, and a low-pressure gas gathering system. The field is expected to go into production in the last quarter of 1992 with peak condensate production of 100,000 barrels a day by 1993. P. 167^ |
