An efficient downhole oil/water-separation system with sucker-rod pump

At present, many oil fields in China have entered the high-water-cut production period, and the water cut of oil wells has continued to rise. Therefore, how to reduce the water cut of the produced liquid, reduce the amount of surface water treatment, shorten the ineffective water circulation, and reduce the comprehensive production cost have become the key problems restricting the sustainable economic exploitation of a high-water-cut oil field. To this end, the development model of circular displacement and the oil-recovery technology of a downhole oil/water-separation system with sucker-rod pump (DOWS-SRP) are proposed. The technology system consists of downhole oil/water-separation devices, an injection/production pump-string system, a sealing system, and downhole data-test system, mainly applied to separating the oil and water in the well through the separation device. The separated water is then directly injected into the formation and the separated concentrated liquid is lifted to the ground so the water injection and oil recovery are completed simultaneously in the same wellbore. The field-test data show that after the implementation of injection/production technology in the same well, the surface liquid-production volume decreased by 90%, the water-cut decreased by 27%, and the water/oil ratio decreased by 93%. In addition, the liquid volume of lifting, gathering, and treatment was greatly reduced, as well as the surface infrastructure investment, to achieve the purposes of cost saving, energy saving, and consumption reduction. At the same time, the downhole reinjection replaces surface water injection, transforming ineffective surface water circulation into effective internal displacement power in the reservoir and improving the yield and recovery rate. The successful application of the quaternary-oil-recovery block has made it possible to redevelop a large number of abandoned oil reservoirs, providing a potential basis for quaternary oil production. In addition, the preliminary energy-saving effect and economic-benefit analysis are performed. The data show that the energy-saving effect of this technology is obvious and good economic benefit is obtained. Copyright © 2020 Society of Petroleum Engineers.