| Application of hydrophobically associating polyacrylamide (HAPAM) in high temperatureand high salinity reservoirs has become one of the hottest research areas of polymer floodingin recent years. In the part of introduction, the preparation, the measurement techniques onflow properties through porous media and viscoelasticities of HAPAM were described.Furthermore, according to the strucure characteristics of HAPAM, some factors influencingoil-displacement capability were discussed from two respects, sweep efficiency and oildisplacement efficiency. The influence factors include the effective viscosity, viscoelasticity,interfacial viscosity, water quality and critical association concentration in porous media.Hydrophobically associating terpolymers (PATT) were prepared by the micellarcopolymerization technique using acrylamide (AM),2-trimethylammonium ethylmethacrylate chloride (TMAEMC) as a cationic monomer, and small amounts of5,5,5-triphenyl-1-pentene (TP <0.5mol-%) as the hydrophobe. The structure ofAM/TP/TMAEMC terpolymer (abbreviation: PATT) was char-acterized by FT-IR and1H-NMR. The evidence for hydrophobic microdomains was obtained utilizing pyrene-probefluorescence. Hydrophobical association propertie were studied in the paper. As expected, theterpolymers exhibited improved viscosity enhancement properties as the concentrationexceeded2500mg/L. Under the same constraints, the apparent viscosity increases withincreasing content of hydrophobic segments. In addition, with other six kinds of polymer, theproperties of salt tolerance, temperature resistance and viscoelasticity were studied in thepaper.Additionally, the flow properties in porous media of two classes of polymers (HPAMsand HAPAMs), including resistance factor, residual resistance factor, effective viscosities anddynamic retention capacity were studied.Influence of permeability and injection rate on effective viscosity was investigated. The calculation formula of effective viscosity wasrevised. The causes of different retention capacity for two classes of polymers have beenexplored in the paper. The results of single molecule force spectroscopy showed that theadhesion force between HPAM and SiO2was about79.5pN. For HAPAM, the adhesion forcewas200-272pN due to different length of hydrophobic segments. Therefore, the absorptionbetween HAPAM and SiO2was much stronger than that of HPAM. The results of dynamiclight scattering indicated the proportion of HAPAM molecules with molecular dynamicsradius bigger than103nm was larger than that of HPAM. So, the entrapment may more likelyto happen for HAPAM in fine pores. Moreover, the adsorption behaviors of two kinds ofpolymer on the surface of SiO2were simulated by Materials Studio. The results showed thatthe absolute value of adsorption energy of HAPAM (477eV) was more than that of HPAM(420eV). This means that the adsorption of HAPAM on the surface of SiO2more likely tooccur. Although associative polymer shows the very high resistance factor, residual resistancefactor and retention capacity by comparison with conventional polymer, the effectiveviscosity of two kinds of polymer didn’t appear to be much different with slightly betterHPAM.Oil displacement efficiency of two kinds of polymer was studied in this paper. Inhomogeneous model, the tertiary oil recovery of HPAM was always higher than that of fourassositive polymers. The tertiary oil recovery increases with increasing the effective viscosityof polymer under the experimental condition. the oil-displacement efficiency of conventionalpolymer HJ is always lower than that of assositive polymer DH5in different permeabilities(0.5、1、1.5、2.5、3μm2) at the same concentration of2,000mg/L. Only in heterogeneous modeland a suitable permeability ratio (about2.8), the tertiary oil recovery of HAPAM is higherthan that of HPAM. Both high and low permeability ratios are not good for oil displacementefficiency of HAPAM.The microstructures of two types of polymers in solution and porous media wereinvestigated by scanning electron microscopy (SEM) to reveal the relationship between themorphology and properties. The specimens were prepared by accelerated freeze-drying inorder to keep polymers with their original morphology without distortion. In aqueous solution, three-dimensional network structure formed in polymer skeletons both in conventionalpolymer and associative polymer was clearly observed. However, the associative polymerexhibited a compact three-dimensional network structure, while only loose network structurewas found in conventional polymer. For assositive polymer, a number of filaments are foundattaching to the polymer skeletons, which are nearly non-existent in traditional polymer. Itwas the reason why associative polymer showed the very high apparent viscosity bycomparison with conventional polymer. However, in the middle of core, most of networksformed by HPAM skeletons are larger and more integrated than HAPAM. For HAPAM, mostnetworks are formed by a limited number of polymer skeletons and have structure defect. Onthe one hand, the retention loss of HAPAM is larger than that of HPAM, causing a reductionin the amount of movable polymer chains in the pores. On the other hand, the narrow space inporous may restrict HAPAM to form the associative structure. That’s why the effectiveviscosity of associative polymer is lower than that of conventional polymer. |
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