Abstract
Refracturing is a key technology in enhancing the conductivity of fractures from hydraulically-fractured wells. However, the deflecting mechanism of the diverting fracture is still unclear. In this paper, a fully coupled seepage-stress model based on the extended finite element method (XFEM) was developed to realize the deflection mechanism of the refracturing fractures. The modified construction of refracturing was then verified by laboratory experiments. Furthermore, two new deflection angles considering the influence area along initial fracture length were introduced to evaluate the refracturing. The numerical results demonstrated that: (1) lower stress difference, larger perforation angle and longer perforation depth can lead to a higher deflection angle, thereby a more curving propagation path of the diverting fracture; (2) increasing injection rate or fluid viscosity can significantly enhance the diverting behavior; and (3) an initial location near the root of the initial fracture results in a larger value of the deflection angle, which is preferred for far-field refracturing. The conclusions in this study can be a systematic guide for the parameter optimization in refracturing treatment.
Highlights
Hydraulic fracturing is an effective way to enhance the simulated reservoir volume to conventional and unconventional reservoirs
An improved model with initial fracture was introduced to analyze the influence of geological data and hydraulic fracturing treatment, including the perforation azimuth angle, perforation depth, injection rate, fluid viscosity, horizontal stress difference, and far-field location of fracture initiation
The results show that a higher value of injection rate can result in a longer curving distance and more curvilinear geometries of the diverting fracture
Summary
Hydraulic fracturing is an effective way to enhance the simulated reservoir volume to conventional and unconventional reservoirs. All diverting fractures were assumed to initiate from the flaws perpendicular to the direction of the in situ maximum horizontal stress This does not correspond to the field application. A fully seepage-stress coupling model based on XFEM was developed to model the diverting fractures in the refracturing process. The accuracy of this model was verified by using the commercial software ABAQUS and experiments [24,25,26]. An improved model with initial fracture was introduced to analyze the influence of geological data and hydraulic fracturing treatment, including the perforation azimuth angle, perforation depth, injection rate, fluid viscosity, horizontal stress difference, and far-field location of fracture initiation. According to the simulation results, the optimization of the refracturing application parameters can be proposed for a successful fracturing treatment
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