The Research Of Rock Physics Characteristics And Brittleness Analysis Of Shale Reservoir

The economic production of shale gas depends on hydraulic fracturing,and Young's modulus,Poisson's ratio and brittleness index are crucial mechanical parameters in hydraulic fracturing technology.Natural shale have the characteristics of sampling difficulty,strong heterogeneity,and many influence factors,these characteristics bring great challenges to shale reservoir dessert prediction.Besides,the petrophysical relationship between reservoir physical parameters such as mineral composition and porosity and elastic parameters of shale are not clear,limiting the application and development of shale sweet seismic prediction technology.Therefore,it is of great significance for shale gas exploration and development to carry out relevant studies on anisotropic shale petrophysics and reservoir brittleness evaluation through the combination of rock physics experiment and seismic physical simulation.(1)Two sets of synthetic shale with different clay types and a set of natural shales were used for triaxial dynamic and static synchronization tests.The results show that the dynamic Young's modulus is always greater than Static Young's modulus,however,the dynamic Young's modulus always increases with the increase of axial stress,while the static Young's modulus first increases and then decreases during loading process.Note that there may be about 30% difference when e estimate static modulus from the static–dynamic relations,which depends on which static modulus is used,providing guidance for the estimation of static modulus using the dynamic and static modulus relation.(2)Taking the advantage of the controllable parameters of synthetic shale,and the influence mechanism of single parameter on shale elastic parameters as the research objective,we investigated the influence of clay content,compaction stress,porosity and water saturation on the elastic parameters of shale,providing a method to estimate the elastic parameters and anisotropy of shale by using clay content and porosity,and providing petrophysical support for shale reservoir exploration and development.Meanwhile,we compared with the existing brittleness formulas,and choose the sensitive parameters,the results show that the brittleness index based on the elastic modulus,especially Young's modulus and Poisson's ratio,is sensitive to lithological changes.The results also show that shale with low Poisson's ratio and middle or high Young's modulus represents the "sweet point" area for shale gas exploitation.(3)Using a Synthetic shale samples with different clay type,together with same comparative measurements on natural shales,the effects of pressure on elastic properties and anisotropy of shale of different clay types were studied.The elastic parameters of shale were sensitive to pressure,and the sayers-kachanov model was used to explain and analyze the stress dependence of samples,so as to provide corresponding petrophysical interpretation for shale reservoirs of different clay types.(4)We constructed a seismic physical models of shale reservoirs with different clay content and porosity to conduct quantitative prediction of brittleness for two sets of shale reservoirs,by combining with rock physics of shale and pre-stack synchronous inversion.It is found that by using prestack simultaneous inversion and optimizing different sensitive factors in inversion results can provide quantitative prediction of elastic modulus and brittleness index in two sets of shale reservoirs respectively,pre-stack inversion results are agree well with the results based on rock physics,which suggest our results of elastic modulus and brittleness analysis are stability and reliability.