Abstract: The natural gas reservoir of Xujiahe Formation and Leikoupo Formation in Jianyang-Dazu field of middle Sichuan Basin belong to tight sandstone gas reservoir and carbonate gas reservoir respectively. The variation of geophysical characteristics of tight sandstone gas reservoir is relatively small, due to low porosity and change of hydrocarbon saturation. So the main challenge for seismic prediction is to predict reservoir and gas strata. Diagenesis of carbonate rocks is so complex that the connection among velocity, density, and porosity is bad, thus it is difficult to predict physical properties of the target reservoir quantitatively. Through prestack seismic data processing and reservoir prediction in Jianyang-Dazu field, following results have been obtained. Firstly, primary factors affecting amplitude-preserved processing of seismic data are analyzed, key techniques for prestack processing are developed, and an effective flow is finally formed. Secondly, petrophysical analysis of typical tight sandstone indicates that elastic impedance (EI) and P-wave-to-S-wave velocity ratio could differentiate lithology effectively; the correlation between P-wave and S-wave as well as porosity is so good that it could be used to predict physical properties. Therefore physical properties are differentiated later than lithology. Thirdly, elastic-impedance coefficient (EC) is developed to predict gas strata in tight sandstone, and new technique to quantitatively predict carbonate reservoir based on seismic techniques constrained by typical reservoir characterization parameters is also presented.

Key words: tight sandstone, reservoir characterization parameter, amplitude-preserved processing, elastic-impedance coefficient, Sichuan Basin