Integrated well placement and fracture design optimization for multi-well pad development in tight oil reservoirs

Multi-well pad has been considered the most efficient horizontal well development technique in unconventional reservoirs since it does not only maximize oil production but also significantly reduces operation costs and environmental footprints by drilling a group of wells on a single pad. To optimize both well placement and hydraulic fracture parameters simultaneously in a multi-well pad is still largely unexplored and remains to be a challenging task. In this study, we develop a global optimization framework based on generalized differential evolution (GDE) algorithm to maximize the expected net present value (NPV) in a constrained well-pad production optimization. More specifically, differential evolution (DE) algorithm is extended for constrained optimization problem through a generalized selection operation. Unlike the penalty functions, the GDE is capable of handling the constraints without introducing any extra parameters. Subsequently, a new well completion economic model is firstly proposed based on a 200 well completion dataset. This enables us to integrate the available field information into the optimization framework and obtain a practical optimum scenario for the multi-well pad development. Furthermore, a geological model is generated and matched to the field production data and operation costs of a four-well pad in Cardium tight oil formation. Based on the newly developed economic model and well-tuned simulation model, the well spacing, well length, fracture spacing, fracture half-length, and fracture conductivity of each well in a multi-well pad are optimized and a highest NPV is achieved. The oil recovery and NPV of the optimum scenario derived through the GDE are increased by 37.2 and 63.7% respectively in comparison with the field reference case.