Three dimensional geocellular and simulation models were developed for an area on the eastern flank of the Ghawar Field in the Arab-D carbonate reservoir that displays anomalous flood front advance and the potential for by-passed oil. Results were achieved through the integration of openhole log data, well performance data, production log data, well test and pressure build up data, core descriptions, 3-D seismic structure, and 3-D seismic influenced permeability distributions. The final products were simulation and geocellular models that were consistent with each other and with all of the available engineering and geologic data. This approach has constrained the resulting models towards a more unique solution that can now be used with greater confidence for reservoir management and the identification of areas of lagging flood front or bypassed oil.
This study was built upon a previous study which showed considerable success through innovations in model layer selection, mapping of very high permeability areas, horizontal and vertical permeability distribution, grid size and relative permeability assignments. However, the incorporation of other data sets, particularly newly acquired 3-D seismic, demonstrated that the predicted distribution of by-passed oil is dependent upon an accurate description of structure, faults and related fractures as well as rock porosity and permeability. The fully integrated modeling approach utilized here was recognized as a superior way to develop a useful simulation model.
This project was accomplished through a multidisciplinary team approach. The team varied in size and membership as the project developed through its various phases. This project integrated the work of reservoir engineers, reservoir simulation engineers, petrographers, geologists, geophysicists, petrophysicists, and geocellular modelers.
This paper discusses the development of an integrated reservoir characterization and simulation model for a very heterogeneous segment of the Arab-D carbonate reservoir of the Ghawar Field in Saudi Arabia. The referenced reservoir segment is roughly 15 km wide by 15 km long and is being depleted by peripheral water injection. Waterflood advance in this area of the reservoir has been extremely rapid. There is therefore the potential of losing oil reserves due to by-passed oil (Fig. 1).
Moore discussed reservoir management issues, well completions and production strategies for this area of Ghawar. In his paper, Moore correlated the fast flood front advance to the preponderance of superpermeability (layers which generally exhibit specific flow rates of 500 BPD per foot or greater). He ascribed the main source of this superpermeability in this part of the reservoir to vugs created after the stick-like organism, Cladocoropsis was leached out from a cased-hardened dolomitized rock at the middle of the reservoir, Zone-2B (Fig. 2).