Performance comparison of smart well design for waterflooding processes

Abstract

A common operational problem encountered during reservoir waterflooding is nonuniformity in oil sweep as a result of reservoir heterogeneity, which consequently leads to early water break-through and reduced oil recoveries. This is mostly due to the heterogeneous nature of reservoirs. Optimal control theory was found to be a very efficient algorithm in determining optimal injection and production trajectories of smart wells that lead the process to optimality. However, the solutions obtained by this algorithm are affected by optimization starting points. In this study, performance comparison of different well designs and at different optimization starting points for improving the efficiency of the waterflooding process was carried out. The study was done on a complex heterogeneous reservoir. The comparison was formulated as an optimization problem, where economic performance of each design was maximized with injection rates and producer bottomhole pressures as control variables. It has been found that optimization starting points affect the performance of vertical wells more severely than horizontal wells. A difference in the net present value due to a difference in initial points of up to 10.85% was found for a particular vertical well design, while 0.04% differential was recorded for horizontal wells. Furthermore, an increase in the number of controls also improves the economic performance of wells. An improvement of up to $8.48 million was recorded for vertical wells. For horizontal wells, this improvement is $14.96 million.