Most common mechanisms of unrecovered oil in reservoirs with bottom water are water coning and cresting. The effects involve a dynamic deformation of OWC, invasion of water to the well’s completion resulting in excessive water production and poor recovery. Coning cannot be controlled by chemical and mechanical water shut-off techniques but the Downhole Water Sink (DWS) method has proven to be effective. Dual-completed DWS wells control coning by draining water from the bottom (sink) completion so the top (oil) completion inflows water-free oil. Despite high productivity and recovery, DWS wells produce large volumes of water that pose environmental compliance problem and cost.

A DWS modification, the Downhole Water Loop (DWL) technique controls water coning without large volumes of produced water (PW). DWL wells are triple-completed so instead of lifting the sink water to the surface, they use downhole pumps to drain and re-inject the water to the same aquifer. DWL wells have environmental advantage of waste volume minimization and productivity advantage of maintaining water drive pressure. Their disadvantage, however, is the need for keeping up with injectivity decline. The objective of this study is to identify economic feasibility of DWL technique for different technical scenarios using reservoir simulator.

Simulation models have been developed to compare economic performance of conventional, DWS, and DWL wells. The Environmental Control Technology (ECT) approach was used to identify productivity and environmental cost benefits for DWS and DWL in relation to conventional well. The results show broad range of conditions where DWS is economically superior to conventional except for high-water-cost areas, where DWL shows best economic performance. However, injectivity decline appears to be the cost-controlling factor for DWL wells.

The comparison of three types of wells, conventional, DWS and DWL reveals benefits of multi-functional wells that improve productivity and reduce pollution. DWL wells could keep water downhole, save energy for water lifting, and control water coning with minimum environmental impact. Also, the case study shows considerable savings in the oil production cost with DWL for oil reservoirs with high-injectivity bottom aquifers in the high water cost areas.

You can access this article if you purchase or spend a download.