Abstract: Problems and challenges related to the reservoir engineering and geomechanics,such as wellbore stability,wellbore integrity and reservoir compressibility are often encountered in the process of horizontal drilling and completion in the shale gas reservoirs with marine facies and complex mountainous landforms in South China.Casing deformation has already become one of the problems hindering the development of shale gas resources efficiently.In this paper,the advance in modelling geomechanic integration,anisotropic tests of rock mechanics and basic research on cementation structure were summarized,and used to develop an excellent shale structure model and a geomechanic model for shale reservoirs in Longmaxi Formation.Taking the shale of Long 11 section as an example,the impacts of mineral compositionscementation structures and shear friction on the steady state-unsteady propagation of fractures were analyzedand revealed the mechanisms of unsteady destruction of shale granule mineral support structures and steady destruction of clay cementation structures.Research results indicated that it is essential to enhance the integration of geology and engineering,and design the fracturing plans staged based on the mineral compositions,cementation structures and geomechanics of the layers indicated in horizontal wells,so as to achieve the efficient development of shale gas in China.