Interaction laws of hydraulic fractures and natural fractures in shale reservoirs
Numerous natural fractures within shale reservoirs will influence the propagation routes of hydraulic fractures in hydraulic fracturing,and clarifying the interaction law between them has directive significance in specifying the reservoir fracture propagation mechanism and optimizing the fracture network.With the use of real shale cores,this paper simulated the interactions between hydraulic fractures and natural fractures in hydraulic fracturing process on the basis of prepositioning a single fracture in advance.The influence of hydraulic fracture approaching angle,depth of injection holes,cementation strength of natural fractures,and confining pressure on the interaction behaviors of hydraulic fractures and natural fractures were studied by using single-variable method.The results showed that three types of interactions were observed:hydraulic fractures opening the natural fractures,deflecting after traveling a certain distance along natural fractures,and penetrating the natural fractures.The maximum slip distance and maximum slip rate at opening were the highest among all interaction results,followed by deflection,and were the smallest for penetration.Compared to tensional fracture initiating,the maximum slip rate was smaller and maximum slip distance was larger under shear fracture initiation.Large approaching angle,small injection hole depth,high cementation strength and high confining pressure are beneficial to the balanced propagation of hydraulic fractures.Otherwise,complicated fracture networks can easily be formed by the communication of hydraulic fractures with natural fractures.The above results have certain reference significance for improving fracture network morphology and optimizing fracturing design of shale reservoirs.
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