Investigation On The In-fracture Diversion Law Of Temporary Plugging And Diverting Fracturing In Fractured Reservoirs

Naturally fractured tight sandstone reservoirs typically have low matrix permeability,thus efficiently activating natural fractures will dramatically contribute to well productivity.However,it is difficult to activate natural fractures by the conventional reservoir stimulation methods in such reservoirs,and the volume of stimulation is limited.During temporary plugging and diverting fracturing technology,diversion agents are injected to bridge and form tight plug within the hydro-fracture,thus increasing the fracture net pressure and activating more natural fractures.Ultimately,the reservoir stimulated volume and well production will be greatly enhanced.Based on the classical intersection criterion of hydraulic fracture and natural fracture,this paper presents the formula to calculate the critical fracture net pressure of the four intersection modes between hydraulic fracture and natural fracture.Then,two calculation methods of plugging strength required for temporary plugging in fracture are established,and corresponding software is compiled for field application.Based on the basic theory of hydraulic fracturing numerical simulation,this paper establishes the finite element model of in-fracture temporary plugging and diverting fracturing in naturally fractured reservoirs.Lastly,this paper investigates the influences of various factors on the process of in-fracture temporary plugging and diverting fracturing.As for the deep naturally fractured sandstone gas reservoir in Kuqa foreland,when the approaching angle increases from 50°to 90°,the total area of natural fracture opening decreases by 17.28%;when natural fracture cementing strength increase from 4 MPa to 10 MPa,the maximum fracture width of the upper and lower branches of the open natural fracture decreases by0.55%and 13.21%respectively;when the horizontal principal stress difference increases from 10 MPa to 16 MPa,the maximum fracture width of the upper and lower branches of the open natural fracture decreases by 15.08%and 22.84%respectively;keeping the constant fluid injection volume,when the injection rate increases from 0.001 m~2/s to0.002 m~2/s,the maximum fracture width of the upper and lower branches of the open natural fracture increases by 13.62%and 11.68%respectively.It shows that natural fractures are more likely to activated in the reservoirs with smaller hydro-natural fracture approaching angle,lower horizontal principal stress difference,lower natural fracture cementing strength and higher fluid injection rate during in-fracture temporary plugging and diverting fracturing.The investigations are of great significance for understanding the mechanism of in-fracture temporary plugging and diverting fracturing in naturally fractured reservoirs and guiding field application.