Optimization of Vertical Well Pattern and Hydraulic Fracture in Offshore Low-Permeability Reservoir: The Role of Low-Velocity Nonlinear Flow

Summary Offshore low-permeability oil reservoirs are an important component of global energy reserves, yet the drilling and fracturing costs are significantly higher than those onshore. Thus, offshore development typically requires fewer wells with higher production, which leads to larger well spacing, wider low-pressure gradient areas, and more obvious low-velocity nonlinear flow. Therefore, there is an urgent need to investigate the nonlinear flow on the well and the fracture design in offshore low-permeability reservoirs. Here, we first establish a reservoir simulation method with multimechanism, including low-velocity nonlinear flow, fracture conductivity reduction, matrix stress sensitivity, complex fault block, and fracture. A grid preprocessing technology is developed to implement embedded discrete fracture on corner point grid. Then, the nonlinear flow parameters are fitted based on experimental data. Finally, the optimal design of well and fracture is investigated. The results show that the staggered well pattern is first recommended, followed by opposite well pattern. As the matrix permeability increases, the recommended well spacing gradually increases, and the fracture penetration ratio and conductivity gradually decrease. The lower the matrix permeability, especially below 10×10−3 μm2, the more significant the nonlinear flow characteristics in the target reservoir block. When the matrix permeability is 2×103 μm2, compared with Darcy flow, the optimal well spacing, fracture penetration ratio, and conductivity differ by 50%, 17%, and 13.6%, respectively.