| Conventional oil and gas exploration and development technology has been very mature,while the development of unconventional oil and gas is still in the stage of rapid development,among which shale gas is one of the most promising and abundant oil and gas resources.One of the most effective ways to detect the distribution of shale gas is through pre-stack inversion.Compared with conventional sandstone reservoirs,shale gas reservoirs have different petrophysical properties,which makes it impossible to analyze shale gas using conventional sandstone reservoir analysis methods.It is necessary to predict shale gas reservoir by establishing TOC sensitive factor using appropriate elastic parameters.The prediction accuracy of conventional pre-stack inversion is not high due to the complicated vertical distribution,wide horizontal distribution and discontinuous variation of shale gas.In order to solve the problem of low inversion accuracy,pre-acquisition inversion can be applied to the prediction of shale gas sweet spots,which can be solved by AVO pre-stack inversion method based on Cauchy distribution under the Bayesian framework.Through the analysis and research of different parameters,such as the wavelet dominant frequency should be close to the real dominant frequency,the initial model should be close to the real underground medium,the noise energy should be removed,and the prior distribution information should be selected as cauchy prior distribution,etc.,it is determined that the prestack inversion based on cauchy distribution can actually solve the difficulties in shale research.Compared with other conventional pre-stack inversion methods,it has obvious advantages.Finally,this method is applied to a test area in southern Sichuan to solve the difficulties of shale gas reservoir distribution,such as large depth difference,complex lateral distribution and few logging data,and to predict the sweet spot of shale gas in this area. |
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