Diffraction Imaging for Detection of Dissolved Caves and Recognition of Fault System on Deep Complex Carbonate Reservoir

Complex carbonate reservoirs in north-western China have enormous potential for oil and gas exploration. Due to their age-old history of sedimentation and great depth (deeper than 6000 meters), the matrix porosity of carbonate reservoirs in Tarim Basin is often less than 2%. The main storage spaces for complex carbonate reservoirs are secondary dissolved pores and fractures which are predominated by visible dissolved caves, fractures and weathering crust. Seismic diffractions carry valuable information related to these geological structures and discontinuities. Thus, diffraction imaging is an effective tool for this type of reservoirs. In this paper, we introduce a novel application of diffraction imaging for accurate detection of dissolved caves and auxiliary recognition of fault system on a deep complex carbonate reservoir. After diffraction imaging, strong diffraction energy can be easily utilized for more accurate positioning of relatively larger dissolved caves while weak diffraction energy is effectively enhanced for better delineating the fault system where dissolved caves and fractures are widely developed. Compared with fracture density result obtained by full-azimuth anisotropic migration in local angle domain and production well information, the proposed novel application of diffraction imaging is proven to be valid.