Composition and Mechanical Properties of Gas Shale

Mechanical properties of shale gas reservoir affect drilling rate.Studying textures and mechanical properties of gas shale can help to provide technical support for drilling designs and operations.Mineral composition,microstructure and mechanical properties for shale cores from southern Sichuan and shale outcrops in Longmaxi Formation,were investigated through X-ray diffraction analysis,electron microscope scanning,triaxial rock mechanical test,etc.The study shows that Longmaxi Formation shale has clay mineral contents of 16.3% to 64.3%,in which illite accounts for 74.0%,but no smectite,indicating low water sensitivity shale;matrix mineral less than 5 μm in grain size accounts for an absolute majority with a small amount of silt-sized debris or grains;uniaxial compressive strengths of parallel and perpendicular to bedding plane are 137.0 MPa and 132.4 MPa respectively,and uniaxial compressive strength in the direction with 45°offset is 66% of that parallel to bedding plane.The study results show that shale mechanical properties are obviously anisotropic.