Influence Of Post-fracture Cavity On Hydraulic Fracture Penetration Of Existing Fractures

For a long time,hydraulic fracturing technology has become one of the core technologies in oil and gas development.How to carry out efficient development through hydraulic fracturing technology is very important for oil and gas production.There are a large number of existing fractures and cavities randomly distributed in fracture-vuggy reservoirs.These existing fractures and cavities have a complex influence on the propagation of hydraulic fractures.Existing studies show that existing fractures have an important influence on the propagation behavior of hydraulic fractures.Domestic and foreign scholars have conducted a large number of experimental analysis and mechanism research on the interaction between hydraulic fractures and existing fractures,and achieved certain results.However,there are few studies on the influence of the cavity behind the existing fracture on the penetration of the existing fracture.These need to be further studied.So it can provide some help for the development of fracture-vuggy reservoir.In view of the complicated hydraulic fracture propagation mechanism in fracture-vuggy reservoirs,this paper carried out hydraulic fracturing research involving a single existing fracture and a single cavity behind the fracture.Firstly,on the basis of fracture mechanics and elastic mechanics,this study established a mechanical model for the intersection of hydraulic fractures and existing fractures under the influence of cavities,and obtained the stress field expression of fracture tip under the influence of cavities on the basis of previous studies.Secondly,a cubic specimen with a single existing crack and a single cavity behind the crack is taken as the research object.We carried out a series of hydraulic fracturing tests on specimens with cavities at different positions and existing fractures with different dip angles,and analyzed the influence of posterior cavities on the penetration of hydraulic fractures through existing fractures.Finally,we use GDEM software to simulate the typical test conditions,and verify the comparison with the test results and theoretical analysis,and further reveal the influence mechanism of the post-fracture cavity on hydraulic fracture penetration of existing fractures.The main results of this study are as follows:(1)The existence of the post-fracture cavity will magnify or reduce the stress intensity factor at the tip of the hydraulic fracture,affect the stress at the tip of the hydraulic fracture,and then affect the expansion of the hydraulic fracture.(2)The existence of the post-fracture cavity will affect the tensile stress region near the side of the existing fracture surface and affect the propagation behavior of hydraulic fractures penetrating the existing fractures.In a certain working condition,the existence of the cavity behind the fracture will make the hydraulic fracture which cannot penetrate the existing fracture penetrate the existing fracture.(3)The existence of the post-fracture cavity will affect the position of the hydraulic fracture passing through the existing fracture.Compared with the case without the cavity,the position of the hydraulic fracture passing through the existing fracture is closer to the region where the post-fracture cavity is located.(4)The existence of post-fracture cavities will affect the propagation path of hydraulic fractures after they exit the existing fractures.The propagation path of hydraulic fractures after they exit the existing fractures is determined by the result of the competition between the direction of maximum principal stress and the tensile stress zone of post-fracture cavities.