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ABSTRACT

Characterizing fractures is essential in effectively developing carbonate reservoirs, especially when they have high porosity but very low matrix permeability. It is important to know and locate fractured areas and define the intensity and orientation of open fractures because they provide the main conduits of fluid flow. Open fractures cause anisotropy in reservoir rocks that may be reflected as a measurable anomaly in azimuthal variation of amplitude or amplitude-versus-offset (AVO), in velocity or travel-time, and in shear-wave splitting. All these anomalies, usually referred to as azimuthal anisotropy, can be extracted from multi-component, wide-azimuth seismic data and after integration with image-log information, can be used for fractured reservoir characterization.

Recently, Occidental Petroleum of Qatar Ltd., who operates under a development production sharing agreement (DPSA) from Qatar Petroleum, acquired over Idd El Shargi fields one of the largest wide-azimuth 3D4C surveys in the region. In this paper, we show results of integration of seismic anisotropy and other fracture-related seismic attributes with image-log information to map fracture intensity and orientation in the Shu’aiba carbonate reservoir. We found that the mean dip-azimuth of open fractures is 137° and the mean dip 81°. The calculated fracture density for the fracture swarms vary from 0.5 to 1 fracture/meter. The results have been instrumental in day-to-day drilling operations and are crucial data in reservoir fracture characterization and discrete fracture network (DFN) model building.

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