Well Trajectory Optimization of Homogeneous and Heterogeneous Reservoirs by the Use of Adjoint-Based Optimization Technique

It is essential to delineate well placement and trajectory of production or injection wells, which is an important step of any field development program. Drilling a well is an expensive process in terms of money, time and effort invested. Being an expensive item, wells must be carefully studied before being drilled. In order to make this process more efficient, this study presents a computer-assisted approach of determining the optimal well trajectory using adjoint-based optimization technique. The algorithm is based on surrounding the injection or production wells with dummy wells; a technique proposed in earlier studies. These dummy wells have a minimal rate of injection or production so as to minimalize their influence on the simulated output. The sum of the gradients of the objective function with respect to the flow rate in each dummy well over the life-time of the reservoir is used to define an improved well trajectory. The whole process is repeated until the maximum net present value is achieved. In order to ensure that the newly optimized well trajectory is drillable, the algorithm restricts the curvature of the trajectory. The optimization algorithm was applied to synthetically generated homogeneous and heterogeneous reservoirs to improve a single well trajectory. Depending on the reservoir, fluid and economic parameters, the algorithms display the adeptness to predict optimized well type and trajectory of wells. Although the optimization results showed a considerable improvement in the net present value of the project, the algorithm can get stuck in local optima.