Downhole water drainage from a gas reservoir for water dumpflood in an underlying oil reservoir

Abstract

For wells drilled in a bottom water-drive gas reservoir, water coning may lead to a considerable amount of water production which diminishes the gas recovery. If the gas reservoir has an oil reservoir underneath, a method called “Downhole Water Drain for Water Dumpflood” (DWDDF) can be performed to drain water from the aquifer underneath the gas reservoir and dump it into the oil reservoir to perform waterflooding. DWDDF technique can help increase gas production from the upper gas reservoir and oil production from the lower reservoir at the same time. In this study, a simple reservoir model having common rock and fluid properties found in Thailand was constructed using ECLIPSE100 numerical reservoir simulator in order to evaluate the performance of the conventional bottom-up production scenario and the proposed strategy of the DWDDF scheme.

The simulation study was divided into two parts: operating parameters and reservoir parameters. For the assessment of the operating parameter, results demonstrate that the best case of DWDDF produces 16.47% more barrels of oil equivalent (BOE) and 94.04% less water production when compared with the best case of the bottom-up scenario. Comparing between bottom-up and DWDDF schemes for different reservoir properties, it was found that gas reservoir thickness and column height of aquifer are key factors affecting BOE recovery as it is related to the amount of gas and water crossflows. Furthermore, the applicability of DWDDF is more effective when it is applied in a gas reservoir with good horizontal permeability and a lower kv/kh ratio.