Abstract: On account of intractable treatment of produced fluid in oilfield and high cost of nanoparticle preparation, rhombic-spherical mixed calcium carbonate nanoparticles were synthesized from produced fluid of Lukeqin heavy oil. Foam stability test and core displacement test were conducted to study the foam stabilization performance of calcium carbonate nanoparticles and the oil displacement effect of the foam system. The results showed that the synthesized calcium carbonate nanoparticles effectively enhanced the foam stability; when the mass fraction of nanoparticles was 0.2%, the salinity of the system was 5 000 mg/L and the temperature was 80 ℃, the foaming volume of nanoparticles was 530 mL, and the foam drainage half-life was 528 s; the foam system had excellent salt and temperature tolerance and adsorption resistance; the water flooding in the reservoirs (water content up to 80%) was converted to foam flooding, and the nanoparticle foam had a stable flooding pressure difference of about 3 MPa, and the recovery rate was increased from 39.84% to 80.16%. Calcium carbonate nanoparticles were stably synthesized by using oilfield produced fluid, which can be used as foam stabilizer to improve foam stability, and can be used in field flooding test to improve foam flooding effect.

Key words: produced fluid in oilfield, CaCO₃ nanoparticles, foam flooding, enhanced oil recovery