STUDY ON STRENGTH CHARACTERISTICS OF MICROPOROUS CLAY IN SHALE BASED ON HOMOGENIZATION THEORY

As one of the basic parameters necessary for shale oil and development, the analysis of shale strength is carried out in the whole process of drilling and hydraulic fracturing. Macroscopic experiments have problems such as sample preparation and time consuming. Limited by downhole conditions, not only the quality of data obtained by geophysical method is not good enough for mechanical analysis, but also it increases the risk of equipment stuck and buried in downhole. In this paper, the strength evaluation method of microporous clay in shale was proposed based on the homogenization theory. The composition and mechanical analysis of porous clay was carried out. Based on dissipative energy principle and Drucker-Prager criterion, the strength evaluation of porous clay was transformed into a solution to the strain of the microscopic \pi function. The mechanical properties of the intergranular pores of clay were discussed and the homogenization strain energy of porous clay was established. The microscopic nonlinear function was constructed based on the strength homogenization theory. A homogenization \pi function was established in relation to parameters such as the composition of porous clay, coefficient of friction and cohesion. Based on nanomechanical experiments, dimensional analysis and finite element simulation, the intrinsic relationship between hardness, strength and composition of porous clay was evaluated. The results show that the elastic modulus and hardness of microporous clay in shale are positively correlated with the packing density of shale. The ratio of hardness to cohesion coefficient exhibits a nonlinear increase with increasing friction coefficient when the clay packing density is constant. The \pi function of porous clay with respect to hardness, strength and clay packing density is solved by dimensional analysis and finite element simulation. The composition and mechanical relationship of shale microporous clay are described. It lays a foundation for further research on shale meso-strength parameters and macro-strength prediction.