Research Of The Evaluation Method Of Fractability Of Shale Gas Reservoir In Sichuan Basin

In this paper,the content of mineral components in shale samples was determined by X-ray diffraction analysis,and the mechanical parameters such as Young's modulus,Poisson's ratio,normalized compressive strength(Cn),mechanical brittleness index(BImer)and permeability were obtained by fluid-solid coupling experiment.By comparing and analyzing the correlation among the experimental parameters,a new model for evaluating shale fracturability in Southern Sichuan is proposed from sensu stricto fracability.Finally,the mechanism of the influence of natural fractures on shale fracturability is studied.The following conclusions and understandings are obtained:(1)Through the study of the correlation between mechanical parameters,compressive strength and mineral content,a new understanding of rock brittleness index and fracturability index is obtained:rock brittleness index represents the potential of fracture formation and preservation,fracturability index represents the difficulty of fracture formation and preservation;(2)The fracturability index FIbm=(WQ+0.49WF+0.51WC+0.44WD)/WT is proposed in this study.The index coefficient takes into account the volumetric modulus of different brittle minerals.Through field application,it is proved that the index has good application effect and prospects in Southern Shu area;(3)The fracturability of shale reservoir(broad sense)is affected by both shale(sensu stricto)fracturability and natural fracture development.When rock-mineral assemblages are similar,the development of fractures in the strata without natural fracture is different from that in the strata with natural fracture.(4)Through this study,the fracturability evaluation method system suitable for shale gas reservoirs(broad sense)in Southern Sichuan is explored,and the permeability change of natural fractures in the process of pressurization is analyzed.The influence of natural fractures on the fracturability of shale reservoirs(broad sense)is considered,which is enlightening for future research.