Numerical Simulation Of Hydraulic Fracturing In Low Permeability Reservoir Based On ABAQUS

With the development of the national economy,China's demand for oil and gas is increasing,and the situation of oil and gas resources is becoming more and more severe.At present,the main high-permeability blocks of most oil fields in China have entered the late stage of development,with almost no capacity.Therefore,improving the production capacity of low-permeability reservoirs and developing various types of unconventional oil and gas resources(shale gas,coalbed methane,etc.)have become hot issues in the current energy industry.As we all know,hydraulic fracturing technology is an inevitable way to improve the recovery of low permeability reservoirs.Only by forming complex fracture network in the reservoirs,reducing the oil and gas seepage resistance and expanding the oil and gas seepage area,can the oil and gas productivity of low permeability reservoirs be effectively improved.However,there are still many problems to be solved when hydraulic fracturing technology is used to exploit low permeability reservoirs in China:(1)Insufficient understanding of fracture propagation mechanism in hydraulic fracturing;(2)Insufficient understanding of the influence of construction parameters on crack propagation;(3)Insufficient understanding of the influence of reservoir stress environment on crack propagation;(4)Insufficient understanding of the crack propagation law of the intersection of artificial cracks and natural cracks,etc.Based on this,this paper makes use of ABAQUS,an international general finite element software,to explore the above four problems,and draws the following conclusions:(1)When the direction of perforation is along the direction of horizontal maximum principal stress,the length of the crack decreases gradually with the increase of horizontal minimum principal stress,but the width of the crack increases gradually.As the angle between the direction of the perforation and the horizontal maximum principal stress increases,the deflection angle of the crack increases gradually and deflects toward the horizontal maximum principal stress,but finally does not deflect to the horizontal maximum principal stress direction.(2)As the viscosity of the fracturing fluid increases,the length of the crack gradually decreases,but the width of the crack gradually increases.This shows that the bigger the viscosity of fracturing fluid,the easier it is to form short and wide fractures,and the smaller the viscosity of fracturing fluid,the easier it is to form long and narrow fractures.(3)As the displacement of the fracturing fluid increases,the length and height of the crack increase,the width of the crack increases and finally stabilizes,and the pore pressure at the injection point is also increasing.(4)When the horizontal maximum principal stress is constant,as the horizontal minimum principal stress increases,that is,the horizontal stress difference decreases,the width and height of the crack increase,but the length of the crack decreases,and the pore pressure at the injection point increases.(5)Changing the direction of the hydraulic crack,it is found that when the prefabricated crack is perpendicular to the horizontal minimum principal stress,the crack is easy to expand,and the length of the crack formed is large,but the width and height of the crack and the pore pressure at the injection point are small;When the crack is parallel to the horizontal minimum principal stress,the crack is not easy to expand,and the length of the crack formed is small,but the width and height of the crack and the pore pressure at the injection point are large.(6)When simulating the intersection process of hydraulic cracks and natural cracks,it is found that the greater the stress difference,the easier the hydraulic cracks extend along the direction of the horizontal maximum principal stress;the larger the angle between the natural cracks and the horizontal maximum principal stress,the easier the hydraulic cracks extend along the direction of the horizontal maximum principal stress;the greater the tensile strength of the natural cracks,the easier the hydraulic cracks extend along the direction of the horizontal maximum principal stress.The crack width and pore pressure at the injection point will suddenly decrease when natural cracks open,but this will not happen when hydraulic cracks directly penetrate natural cracks.