Mechanical Properties and Brittleness Evaluation of Longmaxi Shale Rock of Changning Demonstration Area in Sichuan Basin

Mechanical properties of shale rock play an important role in the development of shale gas.This paper focuses on analyzing the mechanical and brittle characteristics of shale rock by taking the Longmaxi Silurian shale clay of Changning demonstration area in Sichuan Basin as an example by the methods of mineral composition analysis,geophysical log analysis and laboratory mechanics measurement.The mechanical properties(the content of brittle mineral,Poisson's ratio,Young's modulus,brittle rock,and triaxial stress)are compared between the Long 1section and Long 2section of Longmaxi Formation.The results show that Long 2section has higher brittle mineral content than the Long 1section,but the slope of aspect slowness diagrams and Poisson's ratio have the opposite trends,and the Young's modulus from the samples of Long 1section is lower than the Long 2section.The Young's modulus-Poisson's ratio diagram indicates that the Long 1and Long 2section are separation.The shale brittle index of Long 2section is greater than 0.5and the negative strain curve is very steep.The summary conclusions include the Long 2section has a lower Poisson's ratio,lower aspect slowness ratio and higher Young model value,and the Long 1 section is more deformable than long 2.Therefore,the Long 2section is more brittle than Long 1which is better for press crack.