Investigation Of Fracture Plugging And Diverting Patterns In Temporary Plugging And Diverting Fracturing

Field monitoring and indoor investigations reveal that temporary plugging and diverting fracturing(TPDF)technique can generate multiple fractures to improve the overall treatment effects.The TPDF technique can play a significant role in the development of unconventional oil/gas resources.The key of TPDF field operation lies in diverter forming an effective tight plug and subsequent fracture diverting.The process of diverter forming tight plug is influenced by various factors.After plugging the existing fracture,the patterns of subsequent fracture initiation and propagation are more complicated due to the influences of a tight plug and the propped existed fractures.In-depth studies on the patterns of fracture plugging and diverting during are necessary,corresponding experimental methods and simulation techniques have not been developed.This work systematically investigates the diverter plugging and fracture diverting patterns by combining theoretical analysis,laboratory experiment and numerical simulation.The investigations not only provide new methods for the studies of TPDF,but also provide some theoretical guidance for the field operation of TPDF.The main achievements are listed as follows:(1)Analyzed the mechanisms of fracture plugging qualitatively and evaluated the effect of fracture plugging quantificationally.Fracture mouth plugging,in-fracture plugging,and fracture tip plugging can dramatically enhance the wellbore circumferential stress,fracture closure stress,and fluid flow restriction,respectively.Thus the fracture stops propagating due to the enhancement of fracture re-open pressure.Based on the extended finite element method(XFEM),this paper investigates the influences of unevenly distributed fracture net pressure on the fracture plugging effect.The results show tight plug change the distribution of fracture net pressure,and thefracture tip stress intensity factor decreases obviously.Thus the fracture stops propagating.(2)Established a new experimental method of in-fracture plugging with diverters and carry out systematical in-fracture plugging experiments.Fractures with various geometry can be created by controlling the confining stresses.Fracture width can be controlled by the use of steel balls propping the fracture.Diverters can flow in the pipeline smoothly by enlarging the inner diameter of the pipe.The methods above help to carry out the in-fracture plugging experiments.By comparison,a distorted fracture can be plugged faster than inclined flat fracture,axial fracture,or crosscutting fracture.Pure fibers can plug a 1.5 mm wide fracture efficiently,but can not plug a 2.5 mm wide fracture.Diverters tend to plug at the fracture mouth with high concentration,thus the injection time for forming a tight plug can be reduced greatly.The relation between fracture width and diverter diameter determines the success and the speed of building a tight plug.(3)Investigated the characteristics of pressure response and overall fracture geometry of the TPDF technique based on tri-axial hydraulic fracturing experiments.The experimental results verified the feasibility of creating different types of diverted fractures through injection diverters.When the differential stress is 2.5 MPa,the complex diverted fracture network can be obtained easily.When the differential stress reaches up to 7.5 MPa,the diverted fractures were mostly along the direction of initial fractures at high injection pressure.By comparison,powder-shaped diverters plug the created fractures more quickly and induced the injection pressure to increase more rapidly than that of fiber-shaped diverters.Fiber-shaped diverters formed a thicker but less tight plug than that formed by powder-shaped diverters.When injecting fluid without diverters,the pressure response curves typically exhibit an obvious fracture breakdown pressure and a stable propagation pressure.When injecting fluid with diverters,no obvious breakdown pressure and propagation pressure exhibit during fracturing were observed.(4)Numerical investigation of fracture diverting patterns for multiple circumstances during TPDF.In this paper,the numerical methods to simulate diverted fracture propagation during TPDF were built.Based on the simulation results,this paperdefines the concept of deflection angle to quantificationally investigate the diverting patterns of diverted fracture during near-wellbore TPDF.Moreover,this paper defines the concept of deviation angle to quantificationally investigate the diverting patterns of subsequent fracture during horizontal well staged TPDF.By comparing the activation pressure of natural fracture branches,this paper quantificationally investigates the diverting patterns of diverted fracture during in-fracture TPDF.