Combined fluid factor and brittleness index inversion for coal‐measure gas reservoirs

ABSTRACT Gas content and brittleness characteristics, which are mostly quantified using the fluid factor and brittleness index, are the key factors in the evaluation of coal‐measure gas reservoirs, which are similar to traditional unconventional gas reservoirs. However, most previous seismic inversion research and evaluations only focused on one of the parameters. Therefore, in this study, we performed a combined inversion of the fluid factor and brittleness index based on pre‐stack seismic records collected from a typical coal‐measure gas block in the Sichuan Basin. First, a new P–P wave reflection coefficient approximation based on both parameters was derived, and the precision and sensitivity of the inversion parameters were analysed. We then constructed a new inversion equation based on Bayes’ theorem. The logging curves obtained for a typical coal‐measure gas well and through pre‐stack seismic profile were used to evaluate the inversion method. The results of the model test and profile inversion at the well location were in good agreement with the original logging values. Finally, we analysed and discussed the results of the inversion of both parameters for the evaluation of the gas content and brittleness characteristics of the target reservoirs.