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The impact of fault sealing and transmissibility on hydrocarbon entrapment. Case study: Qasr field, western desert, Egypt.


Faults act as migration pathway and lateral seal for the majority of structural traps in the north Western Desert of Egypt. This work aims to define the fault sealing properties and their effect on hydrocarbon entrapment. Seismic interpretation is utilized to build the 3D structural model, including faults, horizons, zones and layering. Lithology and petrophysical parameters were interpreted and analyzed using electric well logs. Reservoir modeling is important to spatially distribute discrete reservoir properties (Facies, porosity, net to gross, shale volume, permeability) within the 3D structural grid. Up-scaling reservoir properties are dependent upon number of layers in each reservoir zone. Facies and petrophysical modeling were performed using the sequential indicator simulation (SIS) and sequential Gaussian simulation (SGS) stochastic algorithms respectively. The structural model of the Lower Cretaceous Alam El Bueib sandstone reservoirs in Qasr Field, showed several three-way asymmetrical anticlines trending NE-SW, dissected by NW-SE trending normal faults. The main oil-bearing sandstone reservoirs are capped by siltstones and shales, and laterally sealed by fault planes. Reservoir heterogeneity, combined with geologic structures, has a good impact on hydrocarbon accumulation. Fault zone properties include shale gauge ratio (SGR), fault permeability and transmissibility multiplier (TM). The study of these properties showed that the majority of faults in the field are sealed in their uppermost part, where hydrocarbons are trapped. Partially sealed faults give rise to hydrocarbon movement through and along fault planes.