| When recovery could not be improved in oil field where polymer was used, much oil remained in reservoir, and some polymer was adsorbed and left in rock pore. The left polymer would depress permeability of reservoir, moreover it could confine the impact of post displacement agent. The polymer used at chinese oilfield almost is polyacrylamide (PAM), which was not degraded hard and its viscosity was great in reservoir. It was figured in academe that microbe is able to degrade remaining polymer in reservoir. Therefore, it should be significative for stable production of oilfield, that new strain able to degrade remaining polymer and flood is screened, cultivated and constructed, and was applied at oilfield after polymer flooding afterward.Four strain of bacteria degrading polymer were screened: JHW-1,JHW-3,JJF and JJH, which belongs to bacillus spp, clostridium spp, Pseudomonas spp and bacillus spp respectively. Under the condition of 45℃,pH6.0～8.0, 4 degrading bacteria could decrease viscosity of polymer 37%～52%, and compound bacterium composed of 4 degrading bacteria could reduce viscosity of polymer about 61%, when polymer became exclusive nutrient source. After sucrose was added to polymer culture medium, 4 degrading bacteria could lessen polymer viscosity 56%～92%, and the compound bacterium debase polymer viscosity 97% around.All 4 degrading strains can produce hydrolase to hydrolyze polymer, and JHW-1,JHW-3 and JJF are able to secret one or a few kind of aiding degrading protein components, which are capable to degrade polymer with hydrolase. JHW-1and JHW-3 would release new aiding degrading protein components to improve degradation performance more, while polymer and glucose or sucrose act as nutrient source. The nonprotein product from JHW-1,JHW-3 and JJH is reducing and capable to promote free radical redox reaction that would make polymer carbon chain rupture, but the product could not hydrolyze polymer. Amide group of polymer degraded could be hydrolyzed much to carboxylic acid and carboxylic ion, which could be a factor leading polymer carbon chain rupture. Hydrolyzing capability of strains would rise evidently,when glucose or sucrose exist in culture medium.A strain of MEOR bacterium, T11, which was capable to release surfactant and looked upon crude oil as nutrition, was determined in this paper. T11 could lower viscosity of crude oil from 64 mPa·s to 34 mPa·s, when sucrose and NH4NO3 contain in crude oil culture medium, under the optimum conditions. When T11 was infused to core and cultured for 7d, recovery would arise 10%～11% than that water flooding. Biosurfactants produced by T11 is detected as rhamnolipid, whose the most yield reaches 1080 mg/L and critical micelle concentration is 39.3mg/L.Fusant, CZ-7, was gained through protoplast fusion between JHW-3 and T11, and its growth condition had no evident distinction compare with the parents. CZ-7 had been cultivated in polymer crude oil culture medium containing 1.0mg/mL sucrose for 7 d, so polymer molecular weight would drop from 18×106 to 0.6×106, and surface tension of culture medium would fall 57.7mN/m to 28.6mN/m, moreover crude oil viscosity would decrease to 30.3mPa·s from 55.2mPa·s, under the condition 45℃,pH7.0. The capability of CZ-7 excesses that of the compoud system containing two parents on the whole.The compound bacteria that CZ-7 had been remixed with JHW-1,JJF,JJH,T11 was named with ZH-3, which had higher capability of degrading polymer, producing surfactant, reducing crude oil viscosity than that had no CZ-7. CZ-7 could degrade polymer and produce surfactant even no adeguate nutrition component, and promote other strains growing, which enhanced the capability of ZH-3.ZH-3 was injected into core and cultured, which would resume core permeability partly, after polymer flooding a long time. Recovery would improve 6.5% compare with polymer flooding, and crude oil viscosity would turn 42.6 mPa·s from 64.7 mPa·s, after ZH-3 culture medium slug that 0.4PV with 1.0g/L sucrose was infused into core and had cultivated for 7d. In heterogeneous strata, ZH-3 would displace more remaining oil in Low Permeability Formation; recovery increased range would turn lower, when permeability ratio augmented.Crude oil belong to heavy crude in Daqing Sabei transitional zone, where MEOR could be implemented. Nutrition substance was little in stratum water, so injeced bacterial liquid should be confected with sewage having much inorganic salt, and living cell concentration should be higher than 106 /mL in field test.
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