ally defined as a permanent permeability reduction after the HPAM solution flows through the porous media), a water-phase velocity, and a lower mobility ratio between the water and oil phases (Wu et al. 2012; Zhang et al. 2015). All these allow higher oil recovery from the larger reservoir volume swept and higher oil-displacement efficiency with polymer fluids. Evidence from pilot tests in the Daqing oil field clearly demonstrates the feasibility and superiority of the HCPF method, which is worth pursuing (Yang et al. 2006b; Denney 2009; Zhu et al. 2013). Yang et al. (2006a) also used high-concentration HPAM solution to conduct flooding studies for a Canadian oil field and illustrated the promising effect of HPAM, showing that it can increase the recovery factor to 21% of original oil in place (OOIP), even though, during the process of HCPF, the oil/water mixture is more easily emulsified and is separated with more difficulty because more HPAM is produced with the liquid. Emulsifications are ubiquitous in oil-production operations, and they are often responsible for oil-productivity impairment and increased production costs associated with transportation and separation, which are more serious in the HCPF process. Emulsions formed without addition of particles or chemicals might be stabilized by polar components in the crude oil such as resins and asphaltenes. Numerous publications have reported that a number of factors could impact the emulsion stability. McLean and Kilpatrick (1997) studied the role of asphaltenes and their interactions with the resins and surrounding crude media in forming interfacial films leading to emulsion stability. Grutters et al. (2007) observed that polar resins, such as naphthenic acids, play an important role in stabilizing the emulsions. Liu et al. (2002) used zeta-potential measurements to study the interaction between bitumen and clay in aqueous solutions. Yang et al. (2007) studied the stability of paraffin/water emulsions, and they argued that the adsorption of particles at interfaces may be controlled by adjusting the electrostatic interaction between particles and the interface without changing hydrophobicity, which is thought to be a main controlling factor of emulsion type and stability. Wang and Alvarado (2008) sampled aqueous phase and oil from a Wyoming reservoir and studied the effect of salinity and pH on emulsion stability. The role of polymer is to further provide stabilization conditions for emulsions, leading to more-complex emulsification behavior. Rigidity of the water/oil interface has been attributed to significant contributions to the suppression of films, hence limiting coalescence. In other words, the rigidity of the surface that is reflected by the rheology is not controlled by interfacial tension in these stable emulsions. At the same time, significant effort has been dedicated to designing protocols to break up harmful emulsions in oil production (Kokal 2005; Nasiri et al. 2013; Liu et al. 2014). Many dehydration methods, such as gravity sedimentation, cent...

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