Numerical Simulation Of Fracture Propagation In Horizontal Well With Rock Mass Of Structural Plane

Unconventional resources such as tight sandstone gas and shale oil and gas have been playing an increasingly important role in the global energy structure.Due to the characteristics of low porosity,low permeability and difficult exploitation of the reservoir,it is necessary to rely on horizontal well staged fracturing technology to develop economically and effectively.It is a prerequisite for fracturing construction design to study the law of fracture propagation in the process of hydraulic fracturing.However,due to the development of a large number of structural planes in unconventional reservoirs,it has typical heterogeneity and discontinuity characteristics,resulting in complex fracture propagation law.In view of the hydraulic fracturing problem of rock mass with structural plane,this paper considers the existing problems in the development of reservoir with structural plane.The dynamic distribution of insitu stress field in hydraulic fracturing process is analyzed,and the fluid-solid coupling equation of fluid flow in reservoir fracture and rock mass deformation with structural plane is established according to the principle of effective stress.Based on the traditional fracture propagation analysis method,the numerical simulation method of globally embedded cohesive force unit is introduced,and the two-dimensional hydraulic fracturing model of homogeneous reservoir and reservoir with structural plane is established by using the finite element software ABAQUS.The following conclusions are obtained through numerical simulation:(1)With the increase of prefabricated fracture Angle,the deflection degree,fracture initiation pressure,fracture extension pressure and fracture extension length increase in homogeneous reservoir single cluster hydraulic fracturing;With the increase of horizontal stress difference,the deflection degree and fracture propagation length increase.Fracturing fluid displacement increases fracture propagation length and fracture extension pressure.With the increase of the spacing of multiple clusters of hydraulic fractures,the initiation pressure,deflection Angle and fracture propagation length decrease.With the increase of the horizontal stress difference,the deflection Angle decreases and the propagation length increases.When the number of simultaneous fracture clusters is 2 to 6,the four clusters have the best effect,the average fracture propagation length is the longest,and the time required for the fracture width to be reduced from the injection point to the initial fracture width is the shortest.(2)In reservoirs containing structural plane,the morphology of structural plane is an important factor affecting the morphology of fracture propagation.When the cementation strength ratio between structural plane and hydraulic fracture is less than 0.6,the hydraulic fracture is more likely to activate the structural plane and propagate along the structural plane.When the intersection Angle between the hydraulic fracture and the structural plane is larger,it is easier for the structural plane to expand at both ends.When the reservoir contains multiple structural planes,the maximum width of hydraulic fracture increases with the increase of structural plane inclination,the fracture propagation length and extension pressure decrease,and the fracture initiation pressure has little difference.With the increase of structural plane density,the fracture propagation path becomes single gradually.With the increase of horizontal in-situ stress difference,the main controlling factors of fracture propagation path change from only structural plane to joint control of structural plane and in-situ stress difference.After activating structural plane,hydraulic fracture will expand along the direction of maximum horizontal principal stress.Considering the simultaneous fracturing of multiple clusters of hydraulic fractures,the simulation results show that: The fracture propagation length is mainly related to the number of activated structural planes,and the maximum fracture propagation length is reached when the fracture cluster spacing is 32 m.With the increase of the fracture spacing,the hydraulic fracture extension pressure increases,while the maximum fracture width and fracture initiation pressure have little difference.When the displacement of the same fracturing fluid volume increases,the fracture initiation pressure and extension pressure increase.However,the fracture propagation length and maximum width decrease.When the number of simultaneous fracture clusters is 2 to 5,the fracture propagation presents the condition that both sides are connected in the middle under the guidance of structural plane,and the average fracture propagation length is the longest when the number of fracture clusters is 3.