Coning Control and Recovery Improvement Using In-situ Water Drainage/Injection in Bottom - Water - Drive Reservoir

Abstract

Abstract Technology that directly controls water coning employs in-situ water drainage using oil wells with downhole water sink (DWS) bottom completions. With DWS, the well's oil productivity dramatically improves as oil can be recovered from a thin pay zone underlain by bottom water – an impossible undertaking for conventional wells. However, concurrent drainage of large volumes of water depresses water drive – particularly in the reservoir systems with small aquifers. A natural extension of the water sink technology for small aquifers is the concept of returning the drained water to the same aquifer using triple-completed wells with downhole water loop (DWL). DWL technology retains all benefits of water coning control without depleting energy of water drive. However, DWL well completions have to be properly spaced to avoid pressure interference and the drained water must be oil-free to be injected in-situ into the same well. The reported simulation study compares recovery performance of conventional, DWS and DWL wells in variety of oil reservoirs with bottom water coning from aquifers of different size and strength. The results show increasing superiority of DWL over conventional and DWS wells in reservoirs with decreasing aquifer strength. For example, when the aquifer is big, the DWL well recovery is similar to that for conventional and DWS wells but is 5-fold slower than that for DWS. However, when the aquifer is small, DWL recovers 60 percent more oil with 43 percent less water in 10 percent shorter time comparing to conventional well, while DWS fails to perform at all due to the fast depletion of reservoir pressure. Also, the simulation experiments demonstrate operational flexibility of DWS and DWL wells. For conventional wells, a small improvement in recovery requires reduced production rate and extended producing time. In contrast, the recovery process of DWS and DWL wells can be optimized for maximum recovery, minimum production time or minimum produced water by seeking the best combination of the oil production and water drainage/injection rates.