| Due to the influence of horizontal stress difference,fracturing fluid viscosity and filtration,the hydraulic fracture did not crack along the tip of the prefabricated fracture,but along the borehole wall,resulting in the failure of the directional fracturing.In view of this phenomenon,this paper takes Zisha rock as the research object,and studies the influence of different stress difference,different viscosity of fracturing fluid and isolation and filtration of prefabricated fracture with waterproof agent,and uses numerical simulation method to simulate and analyze the fracturing process.The main research contents and results are as follows:(1)Through true triaxial physical simulation,the change rule of critical crack initiation angle of different horizontal stress difference is studied,and the crack initiation process is simulated and analyzed.The results show that with the increase of stress difference,the critical crack initiation angle decreases,the fracture opening and fracture velocity increase,and the crack initiation deflection angle,borehole wall deformation and injection pressure gradient decrease.When the stress difference increases from 2 MPa to 4 MPa,the critical crack initiation angle decreases from 90° to 70° and 20°.The fracture opening decreased from 0.15 mm to 0.115 mm;fracture velocity decreased from0.075m/s to 0.064m/s;fracture deflection angle increased from 5.2° to 16.2°;borehole wall deformation increased from 0.023 mm to 0.042 mm;injection pressure gradient in rock increased from 1.74 MPa to 2.37 MPa.(2)Based on the physical simulation test,the influence of different viscosity of fracturing fluid with stress difference of 3 MPa and 4 MPa on the critical fracture initiation angle is studied,and the process of rock fracture initiation is simulated and analyzed.The results show that with the increase of viscosity of fracturing fluid,the critical fracture initiation angle of prefabricated fracture is gradually increased,the fracture opening,fracture fluid velocity and borehole wall deformation are gradually increased,fracture initiation deflection angle and rock are gradually increased The gradient of injection pressure decreases gradually.When the viscosity increases from 1 m Pa·s to 40 m Pa·s and70 m Pa·s,the critical crack initiation angle of 3 MPa stress difference increasesfrom 60° to 70° and 75°;the critical crack initiation angle of 4 MPa stress difference increases from 50° to 65° and 70°;the fracture opening increases from 0.115 mm to 0.175 mm and 0.192 mm;the fracture fracture fluid flow rate increases from 0.064m/s to 0.069m/s and 0.0705m/s;the borehole wall deformation increases from 0.065 mm to 0.072 mm and 0.078 mm;the fracture initiation deflection increases from 0.065 mm to 0.072 mm and 0.078 mm The angle of rotation decreased from 16.2° to 11.7° and 8.8°;the injection pressure gradient in the rock decreased from 2.37 MPa to 1.73 MPa and 0.87 MPa.(3)Through the physical simulation test,the influence of different viscosity of fracturing fluid on the critical crack initiation angle and the process of rock crack initiation after waterproof treatment were studied.The results show that with the increase of the viscosity of the fracturing fluid,the critical fracture initiation angle,fracture opening,fracture fluid velocity and borehole wall deformation increase,and the fracture initiation angle decreases gradually.After waterproof treatment,the viscosity of fracturing fluid increased from 1 m Pa·s to40 m Pa·s and 70 m Pa·s,and the critical fracture initiation angle increased from75° to 80° and 85°.Compared with non waterproof treatment,it increased 25°,15° and 15° respectively;fracture opening increased from 0.173 mm to 0.242 mm and 0.264 mm;fracture fracturing fluid flow rate increased from 0.079m/s to 0.095m/s and 0.098m/s;borehole wall deformation increased from 0.082 mm to 0.093 mm and 0.096 mm;fracture deflection angle decreased from 6.5° to4.7° and 4.1°. |
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