Enhanced Oil Recovery Test Based on Wells and Stations Utilization to Reduce Cost After Polymer Flooding

Abstract

How to improve oil recovery for ultra-high water cut reservoir efficiently is a major technical problem needed to resolve in oilfield development at home and abroad. Currently, the water cut of reservoir and average oil recovery recovery factor have been as high as 95% and 56% after polymer flooding in Daqing Oilfeild, respectively, with 44% of the remaining geological reserves underground showing a great potential for further tapping. During the development of ultra-high water cut oilfield, we should consider reducing the investment cost of the new well drilling and stations so as to decrease cost and increase benefit. Specifically, we re-utilize the spare wells and injection distribution system of the injection stations after ASP flooding tests and significantly reduce investment cost. In this paper, we propose a new scheme of combining spare well station reusing and ASP flooding to further enhance oil recovery for the reservoir after polymer flooding. The field test, with 35 injection wells and 44 production wells, has been conducted in B2X block in Daqing Oilfield to reduce the cost of new drilling wells and new injection stations construction by 31.835 million dollars. By implementing physical simulation experiment to optimize the injection parameters and system formula, we determined that ASP formula for this test is to use polymer with 25 million molecular weight, petroleum sulfonate surfactant and sodium carbonate. The numerical simulation forecast shows that ASP flooding could further improve oil recovery by more than 10 percent. This test has been carried out and good response has been seen. The polymer pre-slug and the ASP main slug were injected in February and May 2015 respectively. Up to October 2017, the accumulated injection pore volume has been 0.61 PV, the injection pressure has risen by 4.2 MPa, the fluid absorption thickness ratio has increased by 31.4%, largest water cut decline of single well has reached 20.8% and the stage incremental oil recovery was 8.13%. Due to the reduced cost of no new drilling wells and no new injection station construction, the field test has achieved good technical and economic development effect. Now, the test area has increased oil by 1.161million barrels (158.9 thousand tons), with 58.07 million dollars economic returns. The prediction via numerical simulation shows that the final incremental oil recovery would be increased by 10.44%, the accumulated increasing oil production would be 1.491 million barrels (204 thousand tons), and the economic returns would be 74.57 million dollars (calculated as $50 per barrel). Through combing largely reducing the investment cost by reusing well station with ASP flooding, this field test achieved good technical and economic development effect. It can be broadly applied in ultra-high water cut blocks after polymer flooding in Daqing Oilfield.