Study On Fracture Propagation Law Of Spiral Perforation And Optimization Of Fracturing For Different Reservoirs

Perforation technology,as an important part in volume fracturing of horizontal wells,can control the fracture trend,improve the reservoir reconstruction volume,and play an important role in oil and gas production.Currently,the commonly used perforation method in the field is spiral perforation,which has shortcomings such as complex fracture morphology in the near wellbore area,and some perforations cannot initiate fracture,and spiral perforation is not suitable for all reservoir conditions.Based on this,this paper,starting from three aspects of indoor experiments,theoretical analysis,and numerical simulation,has studied the initiation and propagation laws of spiral perforation fractures under different factors,determined the reservoir conditions with poor spiral perforation fracturing effects,and conducted targeted optimization simulation of perforation fracturing.The specific work and conclusions are as follows:1.Based on indoor fracturing experiments,the effects of perforation phase angle,perforation depth,and horizontal stress difference on fracture initiation and propagation are preliminarily analyzed.The results show that the spiral perforation phase angle increases,the fracture initiation pressure increases,and the fracture complexity increases.The fracture type changes from tensile type to shear type;The fracture initiation pressure is negatively correlated with perforation depth and horizontal stress difference.Under low stress difference,fractures tend to deflect axially along the wellbore.As the horizontal stress difference increases,the fracture types are mainly tensile,and gradually expand along the vertical direction of the wellbore.Based on the theory of fracture mechanics,the calculation model of perforation initiation pressure is derived,and the influence of different factors on fracture initiation pressure is analyzed.2.Based on the three-dimensional discrete lattice method,a spiral perforation fracture model was established and simulation studies on fracture initiation and propagation under different factors were conducted.The results showed that when the horizontal stress difference was low,spiral perforation fractures were prone to deflect along the shaft axis,while when the horizontal stress difference was high,the non-uniform propagation of perforation was more severe.The fracture toughness of the reservoir increases,the fracture initiation pressure increases,the SRA(Stimulate Reservoir Areas)decreases,and the non-uniformity coefficient increases.The elastic modulus of the reservoir increases,the fracture initiation pressure decreases,the non-uniformity coefficient decreases,and the SRA increases.As the phase angle increases,the fracture initiation pressure increases,and the complexity of fractures near the wellbore increases.As the perforation depth increases,the SRA increases,and the nonuniformity coefficient and fracture initiation pressure decrease.However,the decrease in fracture initiation pressure decreases as the perforation depth increases.The perforation density increases,the fracture initiation pressure decreases,the SRA increases,and the nonuniformity coefficient decreases.The fractures change from independent fracture surfaces at low pore density to petal shaped fracture surfaces at high pore density.The fracturing fluid viscosity increases,the fracture initiation pressure increases,and the SRA and non-uniformity coefficient both increase.As the injection displacement increases,SRA first increases and then slightly decreases,leading to an increase in cracking pressure and a decrease in non-uniformity coefficient.Using large displacement construction can promote uniform expansion of each perforation,increase SRA,and achieve better reservoir reconstruction effects.3.Conduct coplanar perforation simulation and spiral perforation combined with variable displacement fluid injection simulation for low stress difference reservoirs,high stress difference reservoirs,and high fracture toughness reservoirs.The results show that under low horizontal stress difference,using coplanar perforation can reduce fracture initiation pressure and reduce fracture complexity in the near wellbore region,while using spiral perforation combined with variable displacement fluid injection technology has no obvious effect;Under high level stress difference,the most obvious way to enhance the uniform expansion of each perforation and improve the SRA effect is to use coplanar perforation or spiral perforation combined with pulse downflow injection mode;Under the conditions of high fracture toughness reservoirs,the fracture initiation pressure of coplanar perforations is smaller,the SRA is larger,each perforation expands more evenly.When using spiral perforation combined with stepped down injection mode,the SRA increases compared to the constant injection mode,while the non-uniformity coefficient decreases.It is recommended to adopt coplanar perforation mode or spiral perforation combined with stepped down injection mode under high fracture toughness reservoir conditions.