Numerical Simulation Of Hydraulic Fracturing In Brittle Rocks

The hydraulic fracturing technology is widely used in the field of oil and gas production,coal seam gas mining,geostress measurement and other engineering fields.Hydraulic fracturing involves complex physical processes such as seepage,stress,deformation,damage,initiation and propagation of microfracture.It is a hot and difficult problem in the field of rock mechanics.Based on the improved rigid body spring method and combined with the equivalent discrete fracture network model,a two-dimensional rock hydraulic fracturing simulation method is proposed,and the numerical simulation of the hydraulic fracturing of thick walled cylinder model is carried out.The main work of this article are as follows:(1)Based on randomly distributed Voronoi grids,an equivalent discrete fracture network is proposed for the simulation of steady and unsteady seepage in porous media.Meso-infiltration parameters and conversion methods for macroscopic percolation parameters are established.By comparing with the analytical solutions of one-dimensional unsteady seepage flow,the applicability of the equivalent discrete fracture network model is verified.(2)Based on the biot theory,an algorithm for coupling hydraulic pressure and mechanical response was established,and an analytical formula for the hydraulic coupling of a thick-walled cylinder under elastic conditions was derived.The analytical solution obtained by comparison with the known elasticity theory was compared with the numerical solution.This verifies the accuracy of the analytical theory and the proposed numerical model derived in this paper.(3)Combined with the improved rigid body spring method and the equivalent discrete fracture network model,a new discrete mechanics model for brittle rock hydraulic fracturing process was proposed.The influence of the Biot coefficient on the hydraulic fracturing process was studied.Studies have shown that the Biot coefficient as an important parameter reflecting the hydraulic coupling effect has a significant effect on the displacement and failure strength in the hydraulic fracturing process.The larger the Biot coefficient,the smaller the required fracturing pressure.(4)The proposed model is further expanded to explore the influence of confining pressure and unsteady seepage on the hydraulic fracturing process of brittle rock.Studies have shown that under the unsteady seepage frame,the effect of transient flow is outstanding.The peak pressure of the internal fluid under unsteady flow conditions is significantly less than the peak internal water pressure under steady flow conditions.