Abstract:

Aimed at the channeling problem of CO₂ flooding in low permeability reservoir of Changqing, acid resistant nanospheres （AR-NS） were prepared by inverse microemulsion polymerization using acrylamide （AM） as monomer, 4-styrene sulfonate （SSS） and dimethyl diallyl ammonium chloride （DMDAAC） as functional monomers, N, N’-methylene bis acrylamide （MBA） as crosslinking agent, sodium bisulfite and ammonium persulfate as initiators. The results show that the smooth microspheres with high dispersion are found in the emulsion, with an average particle size of 255 nm. The mass retention rate of the acid resistant nanospheres is still about 20%, when the temperature is 450 ℃. It has good temperature resistance. Under the condition of acid formation water, the expansion ratio of the acid resistant nanospheres is 13.8 times, while that of the ordinary nanospheres is only 3.7 times. When the reservoir temperature is 85 ℃ and the concentration is 5 000 mg/L, the viscosity of the suspension is only 0.56 mPa·s, and it has good injectability. The plugging experiment of supercritical CO₂ flooding in low permeability heterogeneous fractured core shows that the plugging efficiency of fractured core is 95.41% and the recovery efficiency is increased by 21.03% after acid resistant nanospheres injection. Acid resistant nanospheres have excellent plugging channeling effect in low permeability CO₂ flooding reservoirs.

Key words: CO₂ flooding reservoir, acid resistance, polymer nanospheres, plugging channeling performance