| Fractured reservoirs are mostly low permeability reservoirs,and the reservoir rocks are relatively dense,and their strength and brittleness are also large,which often produces very complex natural fracture systems.The development and distribution of natural fractures affected the in-situ stress of reservoirs,and further affected the initiation and extension mechanism of hydraulic fractures.Natural fissure is a doubleedged sword.It studies the mechanism of the intersecting of natural cracks and hydraulic fractures,carries out the research work on the cracking and extension mechanism of hydraulic fractures in fractured reservoirs,and improves the recovery rate of fractured reservoirs to reduce and change the natural cracks and ensure the oil industry and social economy in China.It is of great significance to keep and stabilize the hair.In this paper,based on the theory of rock mechanics and fracture mechanics,the fractured sandstone reservoir of Xujiahe,Xinchang area,West Sichuan,is selected as the research object.The geological survey,rock mechanics parameters and natural fracture development of fractured reservoirs are studied and analyzed in order to provide basic data for the study of fracture and extension mechanism of hydraulic fractures.In the study of hydraulic crack initiation in fractured reservoirs,the stress distribution of the surrounding rock and the stress distribution of perforation are analyzed in view of the open hole completion and perforation completion.In view of the three cracking ways of the hydraulic cracks in fractured reservoirs,the judgment conditions for the cracking from the rock body are given and the natural fissure is given.The judgement model of shear cracking is obtained by combining the strength effect theory of structural plane,and the model is solved by the geodetic coordinate system,and the judgment model of opening and breaking along natural cracks is given,and the model is solved by the geodetic coordinate system.Taking a horizontal perforation well in the sandstone reservoir of Xujiahe fractured reservoir in Western Sichuan as an example,the cracking pressure is calculated and analyzed.The calculation results show that the research area tends to crack along natural cracks,which is the same as the actual results.In the study of hydraulic fracture extension in fractured reservoirs,the extended finite element method is combined with the extension of fractured reservoir hydraulic fracture,and the finite element theory of hydraulic fracture expansion in fractured reservoir is preliminarily studied.Two dimensional finite element model for crack propagation is developed.The interaction integral method is used to solve the stress intensity factor at the crack tip of hydraulic fracture,which can be effectively combined with the extended finite element method.The model of hydraulic fracture encountered by natural cracks is studied,the method of judging the extension direction of hydraulic fracture and the calculation process of determining the extension process of hydraulic fracture are obtained.As an example,the sandstone reservoir of the Xujiahe reservoir in Western Sichuan is taken as an example.The results show that the greater the perforation orientation,the greater the deflection of hydraulic fractures,but the hydraulic fracture will eventually turn to the direction perpendicular to the minimum horizontal principal stress,and the hydraulic crack is induced by hydraulic cracks before encountering natural cracks.When the natural fissure is orthogonal to the natural fissure,the tensile stress and shear force of natural cracks are symmetrical.When the hydraulic crack is inclined to the natural crack,the Zhang Yingli and shear stress of natural cracks are asymmetrical;the hydraulic crack is at the low approximation angle.It tends to deflect natural cracks and open natural cracks and extend along natural cracks,and the hydraulic cracks tend to pass through natural cracks directly under the high approaching angle. |
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