Disturbance rule of near-wellbore stress field and casing deformation risk in the process of shale oil well groups fracturing

The development of shale oil and gas commonly adopts the method of three-dimensional well group construction. However, the disturbance of near-wellbore in-situ stress field may lead to issues such as wellbore instability, casing damages, and changes in reservoir permeability, severely affecting the production life span and recovery efficiency of oil and gas wells. In this study, based on the geomechanical finite element method, a three-dimensional numerical model was established by using Petrel 3D modeling software and ABAQUS finite element software. This model was employed to systematically analyze the variation patterns of near-wellbore in-situ stress field during the fracturing process in well groups. Additionally, a risk assessment of casing stress and deformation at various positions along the entire wellbore was conducted. This research indicates that the overlapping of fractured zones from different fracturing stages results in repeated disturbances of the in-situ stress field, which causes the decrease of maximum horizontal principal stress around the well by 25 MPa and the direction deviation angle exceeding 45°, significantly promoting the casing deformation and serving as one of the key contributing factors. When the fractures from horizontal wells within the pad extend into the wellbore region of adjacent wells, the axial displacement of the casings in adjacent wells significantly increases. Numerical simulation results demonstrate that the peak casing displacement in the stress disturbance overlap section sharply increases from 8.25 mm to 36.08 mm, and the maximum Mises effective stress partly exceeds 700 MPa. Furthermore, the repeated and complex changes in the magnitude and direction of the near-wellbore in-situ stress field exacerbate the risk of casing deformation. The numerical simulation results present high coincidence with measured field data, indicating strong engineering applicability of this model. The findings provide important guidance for the design of 3D well groups fracturing and prevention of casing deformation.