In-situ Redistribution of Dormant Gas Reservoir Energy to Maximise Oil Recovery

摘要

This paper discusses a novel development concept of internalrngas injection, in which the energy of gas reservoirs is used tornmaximise production and ultimate recovery of depleted oilrnreservoirs.rnThe South West (SW) Ampa Block 11 field in Brunei isrncharacterised by highly stratified formations containingrnnumerous, often areally extensive, stacked thin reservoirsrnalternated with sealing shales. The sequence contains arnvariation of oil, gas, oil rim and water reservoirs. Due tornfaulting and reservoir shale-out, Block 11 oil reservoirs arernisolated and therefore lack support from an active aquifer. Thernpressures in the oil reservoirs have declined severely, resultingrnin low production rates and a low ultimate recovery (currentrnrecovery factors range from 20% to 40% for individualrnreservoirs).rnA novel development concept of internal gas injection is nowrnproposed to provide energy to the oil reservoirs at low unitrncost. Block 11 contains gas reservoirs that underlie the morernshallow oil reservoirs, and contain an abundance of energy.rnThe internal gas injection scheme will be implemented byrndrilling two “injection” wells. Within each well-bore gas willrnbe produced from the gas reservoirs and injected directly intornthe oil reservoirs. The process will be controlled usingrnintelligent well completions. The scheme will substantiallyrnincrease the oil production rates and reserves. The injected gasrnwill be back-produced both during the proposed developmentrnand after economic oil production has ceased, without loss ofrngas ultimate recovery. The proposed internal gas injectionrnscheme is believed to be an industry first.