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Hydrolyzed polyacrylamide (HPAM) was the traditional polymer and hydrophobically associative water-soluble polymer (HAWP) was the new polymer with three-dimensional network both used to flood to enhance oil recovery. The wellbore area was the most important part before the polymer solution injected into stratum. In this article, the shearing effects of the two polymers were studied by a wellbore simulation device. The viscosities of HPAM and HAWP solutions were both decreased around perforation of wellbore simulation device. Interestingly, viscosity of HAWP recovered from stratum 0.2 m. Until stratum 1.6 m, its viscosity recovered almost 50% of original. The data of intrinsic viscosity showed that the molecular chains of HAWP and HPAM were both degraded without any recovery. The contradiction was further studied by particle size and its microstructure. The mean particle size and particle size distribution data both showed HAWP recovered but HPAM was not. The microstructures of HAWP by atomic force microscopy images further explain the recovery of viscosity. The disassembled molecular chain was self-assembled into aggregate to newly network by hydrophobes with weaker linking than original solution. While the microstructure of HPAM was thoroughly split up to randomly coil without linking. In addition, the viscoelasticity of HAWP was also recovered to some extent but HPAM was not. All the results proved that HAWP has mobility control ability to displace oil in reservoir even if suffered severely shearing by wellbore.

The wettability of oil reservoir rock will affect the oil recovery efficiency by reducing the capillary force. A Gemini cationic surfactant containing double dodecyl chains and two quaternary ammonium headgroups was synthetized and used as a new wetting alteration agent. This paper focuses on the wettability alteration of Gemini cationic surfactants on oil-aged mica mineral surface. The results of contact angle data show that Gemini cationic surfactant have great wettability to alter oil-aged mica surfaces to mid-wetting even weakly water-wet. The adsorption morphology by atomic force microscopy shows that the degree of wettability alteration is mainly dependent on the coverage areas of surfactant molecules. Gemini surfactant formed monolayer on oil-aged mica surface and the monolayer has the trend to from a compact film with increasing concentration. Compared with the single chain surfactant, Gemini surfactant has stronger ability to alter oil-aged surfaces. Considering the flooding experiment in lab results, this Gemini surfactant might be a good choice to be used in chemical flooding.

In the low permeability and high water-sensitive reservoir, water injection may induce the clay minerals hydration swelling and dispersing migration, which are the main factors for formation damages. Sodium montmorillonite, which is easier to hydrate in water than other clay minerals, is usually used to analyze the hydration of clays. A quaternary ammonium salt cationic polymer was synthesized and used as a clay stabilizer. The stability of sodium montmorillonite by interaction with the quaternary ammonium salt cationic polymer was studied, and the swelled clay shrinkage property of the quaternary ammonium salt cationic polymer was also analyzed and assessed by using the XRD, ESEM and visual micro-lithography model from microcosmic points. The results show that the interplanar spacing of hydration swelling sodium montmorillonite observed by XRD decreased as the quaternary ammonium salt cationic polymer infiltrated into the clay and replaced exchangeable cations. ESEM observations show that the sodium montmorillonites were wrapped by quaternary ammonium salt cationic polymer because of the network structure, which could make the size of the hydration swelling sodium montmorillonites smaller. The visual microlithography models confirmed that the clays were wrapped by the quaternary ammonium salt cationic polymer. The hydration swelling and dispersing migration were thus inhibited. Considering the experimental results, this quaternary ammonium salt cationic polymer can play a significant effect on the inhibition of clay hydration swelling and dispersing migration.