It is of great significance to optimize the design of multistage-fractured horizontal wells (MFHW) for increasing recoverable reserves. The main objective of this work is to provide a quantitative assessment of optimal decisions such as number of wells, number of fractures per well, mass of proppant and fracture dimensions. In this study, a rigorous performance simulation of multiwell pad is established to account for the interwell interference caused by varying-conductivity fractures connected to MFHW. Next, a semi-analytical approach is proposed to forecast the transient rate response and investigate the effect of fracture dimensions and completion parameters on estimated ultimate recovery (EUR). Finally, a systematic workflow that optimizes an overall economic objective is developed. The fracture design is posed as nested optimization, where the outer-optimization shell determines the number of MFHW and the number of fractures per MFHW, whereas the inner-optimization shell based on the time-dependent unified fracture design (UFD) involves the decisions on the optimal fracture dimensions. The results show that:
With consideration of technical constraint, the maximum EUR would be achieved on the best compromise between fracture dimensions.
In the condition of optimal fracture dimensions, EUR is monotonously increased with the increase of number of wells (nw) and number of fractures per well (nf).
With consideration of economic constraint, combination of nw and nf determines the achievable recovery and cost. The best accomplishment between nw and nf by balancing production vs. cost can maximize net present volume (NPV).
Under both the technical and economic constraints, when Nprop is relatively lower, more wells and less short-length fractures are suggested to maximize NPV; when Nprop is higher, less wells and more large-length fractures are designed.
This work enables operators to develop a better understanding of the optimum principle, and provides a theoretical guidance to obtain the optimal fracture design of multiwell pad by integrating production-estimation module, UFD module, and NPV module.