Abstract:In view of the difficulties in resuming production after shutdown of the low-pressure high-productivity deep wells in Carboniferous reservoirs in pre-salt Kenjiyake oilfield due to poor formation pressure maintenance, the reasons why the setting depth of conventional multistage-gas lift tools is limited were analyzed, and an innovative approach, i.e., the combination of coiled tubing (as a velocity string) and gas lift technology was proposed for wells with a depth exceeding 4,000 m in pre-salt oilfields. This approach was carried out for the first time worldwide, and has won the national patent of Kazakhstan (№1951 от 22,12,2016г). Theoretically, the deeper the coiled tubing is lowered, the lower the bottom hole flowing pressure is. A larger drawdown will facilitate the formation fluid influx, bring the well potential into full play, and finally achieve a better drainage and production effect in combination with gas lift. At present, the pressure at the gas distribution station of the injection pipe network is 114 atm, and the setting depth of coiled tubing can be 4,000 m or more as suggested by simulating calculation, which exactly satisfies the drainage and production requirements of target zones. This calculation has been verified by a pilot test on running of coiled tubing. This technology works under snubbing conditions, doesn't contaminate reservoirs and meanwhile overcomes the difficulties in resuming production after well killing. The application of this technology reduces the bottom-hole flowing pressure, removes the high water-cut liquid loading at hole bottom and in the vicinity of it, and eliminates the plugging thereof. Reasonable incremental production has been realized in individual wells upon resuming production, achieving sustainable safe production. This technology was successfully applied on the site; the total incremental production from 4 wells reached 42,627 tons. The shutdown wells caused by low formation pressure or failure of production resumption by conventional gas lift were effectively utilized. The successful application of this technology has generated a good effect in incremental production, and provides a technological breakthrough and guarantee for cost-effective operations under the condition of long-lasting sluggish oil price.