TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Hawiyah Jauf Reservoir is a complex structuralstratigraphic 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.
Complicated geology and scarce data are the two major problems in simulation of the subject large carbonate reservoir. Sharp contrasts in permeabilities, ranging from tens to more than one million milli-darcy-feet, are observed in a few hundred meters radius of the reservoir. Field data and past experience in reservoir simulation indicate that the field performance is completely dominated by these super high permeability streaks. Recent studies have shown that these high permeability streaks are very localized. The occurrence of these streaks is random and not correlatable. Consequently, they may be only amenable to geostatistical techniques. The Indicator Conditioned Estimation (ICE) technique described in this paper is designed to honor the spatial structure inherent in the source data and to allow for the prediction of super permeability streaks in areas of no well data. The use of pulsed neutron capture logging and production logging has been very successful in monitoring the sweep of the subject reservoir which is under a peripheral waterflood. At the same time, the logging data has also provided a wealth of information for the model construction; however, only the data derived from dry wells has been used in the past. A new procedure is developed to use information from wet as well as dry wells to augment the database for the model construction. This procedure in conjunction with ICE technique has formed an innovative way to generate the initial permeability distributions for a simulation model. It is expected that this initial permeability distribution should serve as a better starting point for the subsequent history matching process.
Simulation of a large hydrocarbon reservoir that interacts with other producing reservoirs through a common aquifer with a single regular fine-grid model can be very difficult if not entirely impossible. Such a model will require a very large number of cells in order to account for all interactions among the producing reservoirs and still provide enough resolution in the window area being studied.Due to the limitations in computer hardware that can handle the enormous resources required by the model and the solution algorithm, this task is found to be impractical. A two-model approach has been used to overcome this diffiCUlty. In this approach, a coarse-grid, areal model of all reservoirs and the aquifer and a fine-grid, three-dimensional model of the window area of interest are used.The two models are run alternately to feed each other with reservoir rates and boundary conditions while the convergence of boundary conditions is maintained. This approach is found to be resource intensive and requires excessive human effort. This paper discusses the application of the local grid refinement approach as an alternative to the two-model approach to simulate a large hydrocarbon reservoir. The local grid refinement approach involves use of only one model of the reservoir and its associated aquifer system.It allows a finely gridded mUlti-layer model of the reservoir of interest to be imbedded into a coarsely gridded, single-layer areal model References and Figures at end of paper. 457 of its associated aquifer system.Consequently, the number of cells is reduced significantly and it becomes practical to simulate the large hydrocarbon reservoir and its associated aquifer system in one model.For this purpose, therefore, a locally refined grid model was constructed and initialized using data from the already existing models used in the two-model approach.History match runs were made successfully.If compared with the two-model approach, the LRG model history match results are favorable.The LRG model approach is found to be more advantageous than the two-model approach in terms of eliminating the inaccuracies, the excessive resources, and the intensive human efforts associated with the two-model approach. The simUlation results has proved that this approach is feasible and more efficient than the two-model approach. Therefore, the use of this approach will greatly simplify the simUlation of the large hydrocarbon reservoir and its associated aquifer system. IlITRODUCTIONA large hydrocarbon reservoir interacting with other producing reservoirs through a common aquifer, (Figure 1), can be modeled along with its associated aquifer system in a single regular fine-grid model. However, the model will require a very large number of cells in order to account for all interactions among the producing reservoirs and still provide enough resolution in the window area of interest. Depending on the degree of resolution required, this model will end up consisting of hundreds of
This paper discusses a completion scheme currently being applied in a thick, large, elongated carbonate anticline Middle-East oil reservoir. The new well completion calls for a combination of an open hole horizontal section penetrating the top 10 feet of the reservoir and a cased or un-disturbed vertical segment through a thick formation. The horizontal section will be used for producing and the vertical segment will be used for monitoring purposes (Figure-1). The cased vertical segment will allow undisturbed monitoring of the sweep in the area below the horizontal section, especially in areas of high heterogeneity. The horizontal application proved to be useful both in terms of economics and sweep with supported reservoir simulation results and some actual field data performance. Pilot wells have been drilled and completed and early assessment has been encouraging. P. 123
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