ABSTRACT

Regional stress patterns, such as the one in the Gulf of Suez, which is attributed to the Red Sea Rift, give a general indication of the likely fracture orientation or maximum stress trend. However, local variations and the effects of localized structures, such as large faults, can alter the stress pattern completely, counteracting or adding to the regional stress. Such a local stress information can be very important to many petroleum exploration and development related aspects, i.e., hydrocarbon migration, hydraulic fracturing, optimum well placement, welibore stability, and sand production. In this case-study, shear-wave anisotropy data obtained from dipole shear sonic logging over fractured reservoirs in the Gulf of Suez, Egypt, was used to determine the orientation and magnitude of the principal horizontal stresses. The cross-dipole shear data from the DSI Dipole Shear Sonic lmager tool was processed to obtain the oriented fast and slow shear waves. This information was then used to determine the percentage of shear-wave anisotropy, azimuthal rock mechanical properties, the direction and magnitude of the in-situ earth stresses, and the orientation of fractures. Two major zones of anisotropy~ were identified. Zone I showed significant shear-wave anisotropy with a trend along North-South consistent with the Nubia stress trend. The upper interval of this zone was detected as an open fracture system, using the shear-wave anisotropy data in conjunction with the Stoneley-wave fluid-mobility evaluation. This interval was subsequently perforated and produced hydrocarbons. Zone II exhibited an anisotropy azimuth trending along a NW-SE direction, consistent with the known tectonic regime of the Gulf of Suez stress trend (Clysmic fault trend). The stress and fracture information obtained from the dipole shear sonic anisotropy data was subsequently used in the planning of deviated wells, and for fracture treatments.

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