Multi-wave Pre-stack Joint Inversion of Carbonate Formation - A Case Study of Qixia Formation, Middle-Lower Permian, Sichuan Basin

Abstract

AbstractThe study area is Longnvsi (LNS) in the central Sichuan Basin, Western China, and the target layer is the Qixia Formation of Lower Permian, with characteristic of thin dolomite reservoirs, low porosity as well as rapid changes and discontinuity of reservoirs in the lateral direction. It’s difficult to predict reservoirs only by PP-wave data. With the development of multi-component exploration, multi-wave seismic data analysis enhances confidence in interpretation by providing PS-wave data for imaging the subsurface. PS seismic data exhibit significant changes in amplitude and character of seismic events that may not be observed on PP seismic data. When PP and PS data are analyzed together, multi-wave seismic exploration has potential and advantages in fluid and lithology prediction. In this paper, logging analysis is carried out for the target layer, which shows that the reservoir response characteristics of P-wave velocity and S-wave velocity are different, then these sensitive elastic parameters of the reservoir can be determined. By comparing the seismic response characteristics of PP-wave and PS-wave, the reservoir seismic amplitude is also different. The difference between P-wave and S-wave in logging and seism is the basis for PP+PS joint inversion. We tried to perform PP+PS joint pre-stack inversion under the theory of P-wave and PS-wave elastic impedance inversion. In this process, we illustrate some key technologies, such as multi-wave calibration, multi-wave wavelet estimation and PP-PS seismic matching. Compared with PP seismic pre-inversion alone, the PP+PS joint inversion increases the constraint conditions, reduces the inversion ambiguity, gives markedly superior estimates of the P-wave and S-wave impedance and Vp/Vs, and improves the vertical resolution and lateral continuity of elastic parameters. This method has obtained good results in the prediction of carbonate reservoirs in the Lower Permian in the central Sichuan Basin. The lithological interface described is reasonable, especially the distribution characteristics of dolomite reservoirs. It enriches the research ideas for dolomite reservoirs prediction, and it has practical applicability to take advantage of multi-wave data in carbonate reservoir prediction.KeywordsPP+PS joint pre-inversionDolomite reservoirsConverted wavePP-PS wave correlation