f Illumination of Vietnam Basement Fractures from 3D Seismic – A Methodology

Conventional 3D seismic attributes have been used to try identify faults and lineaments within granite or metamorphic basements. However, normal full stack seismic reflectivity has inherent noise and tuning effects contamination that complicates the visualization of subtle lineaments, faults and fractures. Empirically we found the acoustic impedance data derived from the far angle 3D seismic sub-stack was better than full stack seismic reflectivity to image the top basement reflection and better focus faults and image fractures. These localized areas of estimated higher fracture density are seen to be consistent with the interpretation of expected denser fracture areas from the convergence of the larger faults. The far angle seismic acoustic impedance data was processed through the dip and azimuth routine to enhance imaging fracture clusters and fracture trends. The illumination of such sets of fractures, faults and lineaments is facilitated by the use of selective color palette. These first results formed part of the input to new well trajectory design to encounter the basement faults and fractures optimally. The new wells’ FMI analyses confirmed the fracture azimuth sets as predicted.