The Numerical Analysis And Experiment Of Jointed Shale In Hydraulic Fracturing

The hydraulic fracturing is the key process in the shale gas exploration. The shale gas reservoirs with low porosity and permeability is rich in organic matter. The difference of the Jointed shale micro-structure lead to it’s heterogeneous macroscopic properties which has great influence on engineering jointed shale hydraulic fracturing process. Based on it, this paper is desire to use "RFPA-2D" and "RFPA-3D" finite element software to carry out the finite element analysis of Joint shale and plaster samples, and has an analogous experimental research on the plaster samples for the sake of the exploration about the influence of the parameters of jointed shale samples in the hydraulic fracturing process.This paper discusses the existing theory of rock strength in a systematic way and has an analysis in the jointed shale samples which conclude the property of transversely isotropic. Based on it, the theory of jointed shale strength has been explored. With the help of the "RFPA" two-dimensional and three-dimensional finite element software, simulating the hydraulic fracturing process of jointed shale to research the influence in the hydraulic fracturing process with different parameters of jointed shale samples. The uniaxial compressive test of jointed shale gets a different kind of elastic parameters and the curve about mechanical properties. The similar material model method has been used to carry out the experiments about hydraulic fracturing process with plaster model. It’s founded that it’s in good agreement between the test results and finite element simulation results.In this paper the finite element results about fracture pressure is showed as follows: it has a tendency that is dropped after the first rise with the increasing joints angle; it increases linearly with the improvement of the uniaxial compressive strength; it grows fast early and eventually levels off with the increasing of heterogeneity. From the finite element results and the experiment results, it’s showed as follows: the distribution of pore pressure formed in the hole have an annular outward radial diffusion; micro-cracks gradually appears, reach the jointed surface and eventually form the failure surface toward the joints surface throughout the whole rock formation, which indicated that the direction of the crack and the failure surface are mainly controlled by the joints surface.