| Longitudinal slotted hydraulic fracturing is an important technology of directional roof-cutting and pressure-relief in dynamic pressure roadway.Its core is to control the crack’s opening and propagation direction.However,the crack often deflects under the influence of the maximum principal stress in the process of propagation.In order to have a better understanding of the deflection law of the longitudinal slotted hydraulic fracturing crack,consecutively and effectively cut the roof to achieve better dynamic performance.In this paper,similarity simulation test and numerical simulation are used as the main research means.Based on longitudinal grooving bit,the deflection law of longitudinal grooving hydraulic fracturing crack under different horizontal stress ratio,different grooving angle and different pump flow rate conditions is systematically studied,and the deflection of pump flow to longitudinal grooving hydraulic fracturing crack under different horizontal stress ratio is emphasized.The influence of distance is studied in depth.The main results obtained in this paper are as follows:(1)Large-scale true triaxial hydraulic fracturing tests were carried out on the basis of reserved longitudinal grooves of 300 mm*300 mm*300 mm prefabricated cement mortar blocks.Under the condition of stress ratioσ_v:σ_h:σ_H=10:6:9,the cracks started along the groove position and gradually deflected to the direction of maximum principal stress during the propagation process.The cracks showed S-shaped asymmetric shape,and the shape of the cracks was relatively single and not complicated.In the process of increasing pump flow rate from 0.5 ml/s to 1.0 ml/s and then to 1.5ml/s,the deflection distance of crack increases from 131 mm to 203 mm and then to 237 mm,increasing 54.9%and 16.7%respectively,and increasing 80.9%.With the increase of pump flow rate,the deflection distance of crack increases continuously and the increase range is larger.(2)Under stress ratioσ_v:σ_h:σ_H=10:6:12,the cracks begin to crack along the cutting slot position and rapidly turn to the direction of maximum principal stress.The cracks are S-shaped asymmetric and the crack shape is relatively single.The pump flow rate increases from 1.0 ml/s to1.5 ml/s,the crack deflection increases from 62 mm to 81 mm,by 30.6%,the pump flow rate increases from 1.5 ml/s to 5.0 ml/s,and the crack deflection increases from 81 mm to 136 mm.Compared with the horizontal stress ratio of 1.5,the fracture deflection of hydraulic fracturing of each group of pumps decreases significantly.However,with the increase of pump flow,the fracture deflection increases gradually,and there is still a large increase.(3)By establishing a two-dimensional finite element model of longitudinal flume-cutting hydraulic fracturing expansion similar to the true triaxial hydraulic fracturing physical test,the physical test process of each two groups under the condition of horizontal stress ratio 1.5 and 2.0 is simulated,and the numerical simulation results are compared with the corresponding physical test results.The comparison results show that the numerical simulation results are basically consistent with the physical test results.The numerical model has high reliability.(4)A two-dimensional finite element model of hydraulic fracturing expansion for 60 m*60 m large-scale longitudinal slot-cutting is established.Referring to the general mechanical properties of roof sandstone in Tongjialiang Coal Mine,the parameters of the model are set up.The vertical principal stressσ_v and the minimum horizontal principal stressσ_h are set to 10 MPa and 6 MPa respectively.By changing the maximum horizontal principal stress,the simulation of different horizontal stress ratios is realized.By adjusting the initial values,the vertical principal stress ratio is calculated.Fracture angle and pump flow definition value can be used to simulate different grooving angle and pump flow,which provides an effective means to simulate longitudinal grooving hydraulic fracturing process under different conditions.(5)Hydraulic fracturing process under five different horizontal stress ratios is simulated and analyzed under the conditions of groove cutting angle 60 degrees and pump flow 90 L/min.The simulation results show that with the increase of horizontal stress ratio,the fracture deflection tends to decrease,the horizontal stress ratio increases from 1.5 to 2.0 and then to 2.5,and the fracture deflection decreases from 4.05M to 1.81m,then to 0.78m.80.7%,the deflection distance varies greatly with the horizontal stress ratio;the horizontal stress ratio increases from 2.5 to 3.5;the crack deflection distance decreases from 0.78 m to 0.46 m,and decreases by 41%.The deflection distance varies greatly with the horizontal stress ratio.(6)Under the condition of horizontal stress ratio of 1.5 and pump flow rate of 90 L/min,the hydraulic fracturing process under three different grooving angles is simulated and analyzed.The simulation results show that the grooving angle has a great influence on the fracture propagation path.With the increase of the grooving angle,the curvature radius of the fracture deflection curve decreases continuously,but the grooving angle increases from 30 degrees to 45 degrees and then to60 degrees.In the course of construction design,the appropriate grooving angle should be selected according to the actual conditions and needs.(7)Under the condition of horizontal stress ratio of 1.5 and grooving angle of 60 degrees,the hydraulic fracturing process under six different pump flow conditions is simulated and analyzed.The results show that with the increase of pump flow rate,the fracture deflection is effectively weakened,the curvature of deflection curve decreases,the deflection distance increases,and the pump flow rate increases 1.37M from 30L/min to 120L/min.At present,the flow rate of common water injection pump is 90L/min,and the fracture deflection is 4.05m.(8)With the increase of pump flow rate,the crack propagation radius,crack pressure at point F and crack width are all increasing.The increasing crack pressure at point F indicates that the impact of large flow rate will have a greater impact on crack crack pressure in the process of propagation.(9)Under the condition of horizontal stress ratio of 2.0 and grooving angle of 60 degrees,the hydraulic fracturing process under six different pump flow conditions is simulated and analyzed.The results show that with the increase of pump flow rate,the fracture deflection path slows down,the fracture deflection distance increases gradually,the growth rate increases first and then decreases,and the pump flow rate increases from 90 L/min to 150 L/min,a total increase of 0.67 M.At present,the common injection rate increases from 90 L/min to 150 L/min.The pump flow rate is90L/min,and the crack deflection is 1.81m.(10)Under the condition of horizontal stress ratio of 2.5 and groove cutting angle of 60degrees,the hydraulic fracturing process under six different pump flow conditions is simulated and analyzed.The results show that there is no significant difference in the propagation path of cracks under different pump flow conditions,and the deflection distance of cracks remains at about 0.75 m,with no significant change. |
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