Study On Initiation And Propagation Of Oriented Fracturing Hydraulic Fracture For Unconventional Reservoir

Unconventional oil and gas resources are rich in reserves,and their exploitation and utilization have been paid much attention by all countries in the world.As an important part of hydraulic fracturing technology,directional perforation fracturing technology plays an important role in the exploitation of resources in major oil and gas fields in my country due to its advantages in controlling fracture direction and increasing the volume of reservoir reconstruction.However,the current use of directional perforation technology in oilfields only stays at the level of fracturing construction technology and supporting process equipment,and the law of initiation and expansion of fractures is still unclear.As a result,the current conventional fracturing methods often fail to meet the requirements of efficient and stable development of unconventional reservoirs.Based on theoretical research,numerical simulation and experimental analysis,this paper studies the initiation and propagation mechanism of directional perforation fracturing fractures in unconventional reservoirs.First,a true triaxial hydraulic fracturing experiment is carried out to analyze the influence of the horizontal stress difference and perforation parameters on the initiation and propagation of hydraulic fractures.Secondly,the mechanism of fracture propagation simulated by traditional finite element and extended finite element is analyzed to clarify its principle.Finally,the corresponding numerical model was established by ABAQUS software to analyze the influence of factors such as perforation orientation,horizontal stress difference,perforation length,fracturing fluid properties and reservoir related physical properties on the initiation and propagation of hydraulic fractures under the conditions of single-well single-fracture fracturing,single-well multi-fracture fracturing and multi-well fracturing.Based on the research of this paper,the conclusions are as follows:1?Based on the traditional finite element method,the key technology of batch embedding zero-thickness Cohesive elements into the traditional finite element model is realized,and the problem that the traditional finite element method cannot realize the turning and intersection of the propagating cracks is solved.2?The physical experiment results of directional perforation and fracturing show that the morphology of hydraulic fractures can be artificially controlled by directional fracturing,and the problem of increasing the complexity of fractures can be realized.The orientation Angle of perforation,horizontal stress difference and perforation length affect the initiation pressure and propagation pressure of rock and the propagation pattern of fracture.3?Numerical simulation results of single well and single fracture fracturing conditions show that perforation orientation and horizontal stress difference have great influence on the propagation morphology of hydraulic fracture,while fracturing fluid viscosity and formation Poisson's ratio have little influence on fracture initiation pressure and fracture geometry size.With the increase of perforation orientation,the fracture initiation pressure increases,the fracture length decreases,and the fracture width decreases first and then increases.With the increase of horizontal stress difference,the fracture initiation pressure increases,the fracture length increases,and the fracture width decreases rapidly at first,then the decreasing rate slows down.With the increase of perforation length,the fracture initiation pressure decreases rapidly at first,and then the decreasing range decreases.The fracture length increases at first and then decreases,and the fracture width increases.When the total amount of fracturing fluid injected is constant,the injection displacement increases,the fracturing pressure decreases,the fracture length decreases,and the fracture width increases.The Young's modulus of the formation increases,the fracture initiation pressure decreases,the fracture length increases,and the fracture width decreases.The tensile strength of the formation increases,the initiation pressure increases,the fracture length decreases rapidly,and the fracture width increases rapidly.4?Numerical simulation results of single-well multi-fracture fracturing conditions show that the propagation path,fracture initiation pressure and fracture geometry are greatly different from those of single-well multi-fracture fracturing due to the interference of induced stress between fractures.When the perforation orientation,perforation phase Angle,horizontal stress difference and formation physical property are changed,the initiation pressure and fracture geometry size are changed regularly.5?The numerical simulation results of multi-well fracturing conditions show that under the condition of multi-well fracturing,the hydraulic fractures generated by different Wells will present regular changes,and the fracture length and width of fractures seriously disturbed by the stress between hydraulic fractures are shorter and larger,and the initiation pressure of rock is higher.