The goal of this paper is to investigate the near-wellbore phenomena with respect to fracture initiation. The 2D numerical model was developed, which takes into account the interaction of steel casing, cement, and surrounding rock and allows for a curved path of the fracture. The model incorporates an effective finite-difference numerical method for solving a system of coupled differential equations: 1D equations of power law fluid flow along the fracture trajectory and 2D equations of the linear elasticity for rock massif. The model predicts and evaluates the near-wellbore fracture pinching effect as a function of fracture trajectory, perforation misalignment angle, cement/formation properties, stress contrast, and fracturing fluid parameters.

The model developed has a limitation: it does not take into account the leakoff and pore pressure changes in near-wellbore zone during fracturing treatment. However, we believe that this limitation is not essential as it does not affect the quality of results obtained and can be eliminated easily.

Several different scenarios of fracture initiation and propagation were considered. We modeled the initiation and propagation of the fracture through the narrow channel (microannulus) along cement-rock interface as well as along the misaligned perforation. We also investigated different geometries of microannulus development and made conclusions on the most probable situation for different formation conditions. We conducted the comparative analysis of pressure drops and fracture width reductions for different types of fracture propagation. We also modeled fracture propagation for different perforation phasing angles. Based on the results of numerical experiments, we are able to provide some recommendations on how to avoid the worst case of the fracture initiation scenario.

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