A Study On Microbial Blockage-removing Technology In Polymer Injection Wells

The polymer flooding technology has been put into industrial application in many oilfields as Daqing, Shengli etc. As the incremental injection volume of the polymer solution, the injection pressure increase gradually year by year and especially there were some cases that the polymer solution can not be flooded normally. The difficulty in polymer injection has great effect on the oil displacement. The reason mainly lies in the fact that the long chain of high molecular polymer can block the subsurface pores and channels and then reduce the fluid flowing ability in the formation. In this research a sort of bacteria capable of degradation of the partially hydrolyzed polyacrylamide (HPAM) is flooded into the formation towards the residual polymer to dredge the pores-channels and reduce the pressure, so as to unplug the formation and increase the injection volume.The strain of the PHPA degradation bacteria (BL2) was screened from the water production of an oilwell at the polymer flooding block. By static degradation experiment at lab, the culture medium formula and the optimum degradation conditions were determined. That was at 45℃and by pH 7.3, on the basis of crude oil as carbon source and NH4H2PO4 as Nitrogen source, ten percent of the inoculum concentration was mixed with the PHPA solution for eight hours. The results indicated that the percentage loss of the solution viscosity reached 36.2% at the point of the lowest solution viscosity and the relative molecular weight had been reduced by a order of magnitude.The simulated experiment by the unplugging bacteria in homogenous cores showed there was obvious reduction of the injection pressure for cores with different permeability and the reduction magnitude was over 50%.The simulated experiment on pressure reduction with heterogeneous cores showed that after injection of the HPAM solution there were pressure reductions at all the inlet, the testing point of high permeability and the testing point of low permeability by 51%, 43.9% and 28.3%, respectively.The studies proved that the strain BL2 can degrade the retained HPAM, so as to improve the injection capacity, finish the quota of polymer injection and to enhance the overall oil recovery at the oilfield to a satisfactory level.