Seismic sedimentology study of braided river — A case study in He8 and Shan1 members of Permian, Sulige western region, Ordos Basin

Abstract

The He8 and Shan1 members deposited by braided river are major pay zones of the Sulige western region, Ordos Basin. In these two members, the P-wave impedance ranges of gas-bearing reservoir and the surrounding lithologies are highly overlapped. The gas-bearing reservoir cannot be feasibly recognized by the conventional poststack seismic data. In addition, the seismic reflection of the Shan1 member showing mid-weak amplitude distributes discontinuously within the whole seismic survey, leading to difficulties in tracking seismic events and delineating the plane map of reservoir distribution. To solve the problems above, a seismic sedimentology study was conducted in the study area. First, the seismic reflection characterization of braided river was studied according to its sedimentary model. Also, the amplitude variation with offset (AVO) seismic data were used to identify gas-bearing reservoir because the Poisson’s ratios of gas-bearing reservoir and the surrounding rocks are distinctly different. The AVO attribute volume is therefore converted into the lithologic volume, which is useful for the subsequent lithologic interpretation work. The isochronous surface of the Shan1 member seismic reflection can be achieved with the aid of a stratal slicing technique. The practice indicates the feasibility of lithologic converting of the AVO attribute volume. The gas-bearing reservoir of the He8 and Shan1 members can be precisely predicted, and the evolutional history and plane-distribution character of the gas-bearing reservoir are clearly delineated by the stratal slices with isochronous significance.