An integrated study on fracture prediction using 3D P-wave field seismic data

Abstract

An integrated study on fracture prediction by analyzing seismic anisotropy within a 3D P-wave seismic data set from an oilfield in Northwest China is performed. The research area is dominated by a regional anticline and the target layer is a fractured gas reservoir at a depth of approximately 3 km under the anticline. Two major aspects are considered. First, two P-wave poststack attributes (reflection strength and frequency content in selected lines) are extracted and their features in the target layer are examined, looking for the possible fracture distribution in two prospective zones. Second, the azimuthal attribute analysis approach is applied to estimate fracture density and orientation in the whole area from the prestack data (amplitude and traveltime). The result from the poststack data indicates the high possibility of fracture distributions in these two zones, and the prediction from azimuthal amplitudes in the prestack data is consistent with the fracture orientation from the well interpretation and the observation of outcrops at the top of the anticline but suffers from a poor offset-depth ratio and acquisition footprint. The prediction from azimuthal traveltime is strongly influenced by the regional anticline structure and, therefore, is not reliable. Nevertheless, the prediction from post- and prestack attributes provides more details of the fracture distribution in the target reservoir, which can expand understanding of the reservoir fracture distribution.