An Environmentally-friendly Method for Removing Polymer Plugging in Well Boreholes

With the progresses of industrial scale of high concentration and high molecular weight polymer flooding in Daqing oilfield, there are severe polymer plug problems, which occur in the perforated zone and the interstices of the formation adjacent the perforated zone. In attempts to remove or at lease reduce these polymeric build-up plugs, the strong oxidants are widely used in oilfields. The use of oxidants is undesirable because of the high price and short efficient period. What is more, it cannot meet standards of safety and environmental protection. This article presents lab and field test results of this removing polymeric plug method based on microbial degrading polymer. Lab experiments results show that polymers with different molecular weights were efficiently degraded by screened bacteria under different reservoir temperatures. It can be seen in visualization model that polymer plugs in pore were removed obviously. The polymer injection pressure was decreased 25%. The pilot tests in Daqing oilfield showed that by applying the method, average injection pressure of each well was decreased 435 psia, the average effective period reached to 520 days, and more than 7,000 barrels (bbl) of oil were increased in the test field.