Research On Coal Rock Permeability Evolution Under Fluid-Solid Coupling And Reservoir Fracturing Enhancement Mechanism

The effective transformation of hydraulic fracturing to the original form of coal reservoirs is an important prerequisite for coal mine shafts to release pressure and increase permeability and increase production.Hydraulic fracturing allows high-pressure water injection to expand and extend the reservoir micro-fracture network under the effect of geostress and water injection pressure,thereby improving the reservoir permeability.It is of great significance to study the damage and fracture and permeability evolution rules of coal-rock fluid-solid coupling for revealing hydraulic fracturing and permeability enhancement of reservoirs.This paper focuses on the elastoplastic damage model of coal and rock,fluid-solid coupling model.Through theoretical analysis and numerical simulation,it systematically analyzes the damage failure and permeability evolution process under the fluid-solid coupling of coal and rock.Based on the fluid-solid coupling coal rock damage and permeability evolution law,the hydraulic fracturing enhancement characteristics of coal reservoirs were revealed.The main tasks as follows:(1)An elastoplastic damage model based on plasticity and damage theory is used to characterize the mechanical properties of natural coal and rock.A plastic damage variable that considers the homogeneity of coal and rock is introduced and combined with numerical experiments to analyze the plastic damage parameters of coal and rock.The homogeneous coal rock damage evolution equation,using laboratory test results to verify the reliability of the numerical simulation method and the applicability of coal rock damage evolution to the post-peak plastic deformation state.(2)According to the fluid-solid coupling theory,the macro-mechanical characteristics and permeability change law of coal and rock deformation and failure are studied,combined with the characterization primitive method,the permeability evolution equation considering the overall damage effect of coal and rock is proposed.Comparing the laboratory test results,the numerical simulation of coal and rock permeability The effectiveness of the test process.At the same time,considering the influence of coupled confining pressure,osmotic pressure,and homogeneity on coal rock deformation stress and seepage field evolution,the formation process of coal rock plastic damage and fracture area was analyzed.(3)Based on the evolution law of coal rock damage and permeability under fluid-solid coupling,taking coal reservoir fracturing enhancement as the research background,the change law of reservoir stress and seepage field under the effect of in-situ stress and water injection pressure was analyzed.The evolutionary process of the formation of plastic fractures and fractures in the formation of complex fractures reveals the mechanism of hydraulic fracturing and permeability enhancement in reservoirs.