Abstract
The method of nanofluid flooding to enhance heavy oil recovery has attracted much attention in oilfields. An EOR technology named alkali-silica nanoparticle-polymer (ANP) flooding was designed to enhance heavy oil recovery. The performance of the ANP flood system on reducing interfacial tension (IFT), altering the wettability of rock surface, emulsifying and displacing heavy oil were compared with that of polymer (P), alkali-polymer (AP) and nanoparticle-polymer (NP) flood systems. Visual flooding test was conducted to investigate the displacement mechanisms of different flood systems in porous media. ANP nanofluid could remain stable over 30 days without sedimentation of nanoparticles. The emulsifying ability of the four flood systems for heavy oil followed the order: P < NP < AP < ANP. Based on the analysis of droplet size distribution of emulsion and changes of IFT value with alkali concentration, the best formula of ANP system to emulsify heavy oil was 0.3% [w/v] Na2CO3 + 0.1% [w/v] silica nanoparticle + 1000 mg L~(-1) polymer. Electrostatic repulsion between silica nanoparticles and oil droplets played a dominated role on stabling ANP emulsion. ANP flood system could change the wettability of rock surface to a more water-wet state (contact angle varied from 85.4° to 35.6°). Core and visual flooding tests proved that ANP flood system had a better sweep and displacement efficiency for heavy oil than other three flood systems (P, AP and NP), which could enhance heavy oil recovery by 21.19% after water flooding in a sandstone core. Emulsification is the main mechanism for ANP flooding to enhance heavy oil recovery.
NSTL