The Bohai Bay Basin is very rich in heavy oil. Generally the water flooding recovery of heavy oil reservoirs is only 18-20% in Bohai Oilfield, which has great potential for EOR. Being a mature technology in onshore oilfields, polymer flooding in Bohai Oilfield faces a serious of difficulties including choosing the best polymer injection opportunity in limited platform life, poor applicability of existing polymers and polymer preparation and production fluid treatment restricted by platform space. In recent years, several large heavy oil fields have carried out chemical flooding test. In order to solve the above problems, the early stage polymer injection development mode which breaks the limit of secondary and tertiary oil recovery was practiced to fit the service life of platform; a new kind of hydrophobic associative polymer was designed to meet the demand of viscous crude oil, high hardness water, strong shear force and large well spacing in Bohai Oilfield; a serious new facilities used for polymer instant solution and production fluid treatment was designed to fit the narrow space of platform.
The tests show that the early stage polymer injection development mode in offshore heavy oil fields has achieved good results. It effectively reduces or stabilizes the water cut and increases oil production significantly. Based on the good test results, the scale of injection test in Bohai Oilfield expands continuously. It develops from 1 injection and 5 production in a single well group to 44 injection and 171 production in three oilfields, with polymer flooding reserves reaching 144×106m3. According to statistics, in the recent 5 years, the cumulative oil production of polymer flooding has reached 5.651×106m3, and the recovery rate is increased by 3.9%, which is expected to be 8% in the future. Successful application of the technologies has significantly improved the development effect of offshore heavy oilfields. Even in the low oil price period, it has created tremendous economic value for the company. Nowadays polymer flooding has become a necessary means of stabilizing oil and controlling water in old oilfields in Bohai.