Features of buried hills fracture and fracture-cave reservoir prediction in Y Gas Field of the Qiongdongnan Basin based on curvelet transform

The prediction of fractures in the Mesozoic granite buried hills in the Qiongdongnan Basin in the northern South China Sea is difficult, and the lack of wide azimuth pre-stack seismic data would result in the inability to carry out AVAz inversion. The low seismic signal-to-noise ratio in the target layer of buried hills would generate poor prediction of fractures using conventional seismic attributes (coherence, curvature) analysis. Rock physics analysis of the granite buried hill in the study area indicated that the heavily and moderately weathered zones of the buried hill reservoir exhibit low S-wave impedance, while the interior fracture zones of the buried hill demonstrated high S-wave impedance. Based on the stacked seismic data after gather optimization, curvelet transformation, ant-tracking, and maximum likelihood attribute analyses were conducted; shear-wave impedance inversion were performed to obtain the relative shear-wave impedance, and the analysis of buried hill reservoir were completed. Results show that the ant-tracking attribute and maximum likelihood attribute after curvelet transform could characterize large and medium scale fractures and internal details, and the characterization effect is better than seismic curvature attribute. The shear wave impedance after curvelet transform could reliably characterize the weathered zone reservoir of granite buried hills. By integrating the ant-tracking attribute, maximum likelihood attribute, and S-wave impedance results of the curvelet transform, the development model of the Mesozoic granite buried hills in the study area was established. The prediction results of the buried hill reservoir have been confirmed by drilling data, achieving good prediction results. The above-mentioned method is not only applicable to the prediction of granite buried hill fractures and weathering zones, but also provides a reference for the prediction of metamorphic rock buried hill reservoirs, and has good applicability in similar regions.