Study On Hydraulic Fracturing Mechanism Of Rock-like Materials Based On FVM

Hydraulic fracturing is a fluid solid coupling process,but at present,the research on hydraulic fracturing mechanism is seldom considered the coupling effect of the actual fluid seepage and the formation stress.On the basis of various assumptions,the traditional fluid solid coupling theory is still unable to consider many practical problems,such as microparticles blocking pores and clay particles water absorption and expansion.Therefore,it is of great practical significance to describe the coupling between formation stress and fluid seepage in hydraulic fracturing more comprehensively and accurately.This paper takes the rock-like material as the research object,the mechanism of hydraulic fracturing is discussed through experimental research,theoretical analysis and numerical simulation.(1)The conventional mechanical test and permeability test are carried out.The concept of stress sensitivity introduced into the permeability is considered with clay content,the parameters of conventional mechanical parameters and permeability characteristics are obtained,and the influence rules of the permeability are analyzed.It is found that the stress sensitivity increases with the increase of clay content.The stress sensitivity modulus M of permeability is used to characterize the effect of effective stress on permeability,and the relationship between the modulus M of stress sensitivity and clay content is in accordance with the two order polynomial.(2)Based on the theory of elastic mechanics,rock mechanics and seepage mechanics,the cracking mechanism of reservoir rock and indoor physical simulation test is analyzed;And the cracking criterion is discussed,the initiation criterion of hydraulic fracturing should not only include the maximum tensile stress criteria for the opening of the perforated surrounding rock,but also the criterion of the crack initiation of the wall rock at the maximum horizontal stress.Then based on the seepage mechanics analysis,the mechanism of the cracking and the percolation mechanism are combined with the stress sensitivity law of the permeability obtained by the test results.The hydraulic fracturing mechanics model considering coupling effect is constructed,it can not only determine the initiation pressure of perforated surrounding rock,but also accurately calculate the initiation time.(3)Based on the finite volume method(FVM),the mechanical model is solved by programming,the spatial and temporal distribution of pore fluid pressure can be obtained by numerical calculation,which can not only determine the position of the rock crack,but also analyze the influence of the increase of the stress concentration caused by the increase of the pore pressure in the near well area.And the numerical simulation of the model considering and without considering the stress sensitivity under different working conditions is carried out respectively.The hydraulic cracking mechanism is discussed from two aspects of the initiation pressure analysis and the fluid seepage analysis.