| The author’s research group had obtained non-linear acrylamide polymer with heat-resistance above85℃and higher salinity than100g/L, and can be used for flooding oil under high temperature and high salt reservoirs, but the critical association concentration of this kind of copolymer was high (1g/L or higher). This paper aimed at obtaining copolymers PSAn with different branched chain length and reducing the critical associated concentration of oil displacement agent, in order to decrease flooding capacity and the flooding cost through the synthesis of surfactant monomerSMAn(n=4,20)with different chain length,salt-resi stance and heat-resistance. Solution properties,flooding performance, and adsorption performance in the quartz sand surface about PSAn were studied. Microscopic associated structure, hydrophobic associating mechanism and molecular chain size of copolymers PSAn in water and brine solutions were deeply systematic studied, and the relationship of molecular structure, supramolecular association structure and properties of non-linear copolymers was revealed.At30℃, for copolymers PSA4and PSA20, the critical associated concentrations were0.8and0.5g/L in water,0.5and0.3g/L in70g/L NaCl brine solutions respectively, and their viscosities in brine solutions were significantly higher than in water. Copolymers PSA4and PSA20in brine solutions all exhibited strong viscosifying ability and unique salt-thickening behavior twice, and viscosifying ability of PSA20was stronger.In0～110g/L NaCl solutions, the apparent viscosities of the two copolymers solutions in70and100g/L NaCl solutions had reached maximum value twice, respectively, the viscosities were835.8and741.8mPa-s for polymer PSA4with a polymer concentration of2g/L,1019and829.8mPa-s for polymer PSA20with a polymer concentration of2g/L.In0～160g/L CaCl2solutions, the aqueous PSA4and PSA20solutions with a polymer concentration of2g/L all exhibited apparently salt-thickening behavior in140g/L CaCl2solutions, and the apparent viscosities were865mPa-s and1089mPa-s.Polymers PSAn in70g/L NaCl solutions exhibited heat-thickening phenomenon within the scope of25～30℃, but there was no heat-thickening behavior in pure water within25～80℃.Copolymers PSAn solutions also showed good activity in surface and interface, and PSA20had better activity in surface and interface than PSA4For1g/L polymer PSA20solutions in water and in70 g/L NaCl solution, respectively, the surface tensions were27.51and22.02mN/m, and the interfacial tension were1.97and0.07mN/m.Through the simulation of high temperature(80℃) and high salt(about120g/L) reservoir conditions of a block of zhongyuan oilfield, the results of displacement experiment on different polymer concentrations in permeability range of65～90(10-3μm2) indicated polymers in concentration range0.3～1g/L of low polymer dosage range all had achieved high resistance coefficient and residual resistance coefficient, more than14and3.5respectively. The displacement curve of0.8g/L PSA20brine solutions in permeability range within75-340(10-3μm2) showed that, PSA20within the medium scope of permeability all had achieved high resistance coefficient and residual resistance coefficient, more than14and3respectively. By comparing injection performance of PSA20and HPAM indicated that, for polymer PSA20, the resistance coefficient and residual resistance coefficient in the porous medium were apparently bigger than HPAM, which indicated that the non-linear polymer PSA20had better ability to reduce the water-oil mobility ratio and the hydrofacies permeability in high permeable zone than linear polymer HPAM.Results of flooding oil efficiency experiments indicated that polymer PSA20showed excellent application prospect in high temperature and high salt reservoir by a further12.5%recovery ratio on the basis of water flooding.The polymer PSA20static adsorption experiments in quartz sand showed that when liquid-solid ratio was10mL/g, adsorption capacity had reached equilibrium. Adsorption capacity along with the change of initial concentration had isothermal adsorption curve characteristics of typical lundgren muir type.The adsorption capacity of PSA20became stability when the adsorption time was24h. The adsorption capacity of polymer PSA20on the surface of quartz sand was decreased with increasing temperature, which was in contrast to the change process of linear polymer HPAM reported by literatures.Adsorption capacity of PSA20was increased firstly and then decreased with increasing salinity,and the maximum adsorption amount was923.31μg/g.The method of combining ultraviolet spectrum with fluorescence spectrum through pyrene probe was used for investigating the formation of hydrophobic micro-environment for the PSAn copolymers solutions. With increasing the polymer concentrations in water and70g/L NaCl solutions, resulting the increase of absorbance A, the decrease ofI1/I3values, and the increase of Ic/Im values. In different concentrations of NaCl solutions, when the concentration of NaCl was70g/L, absorbance A and Ie/Im values all reached the maximum, besides,I1/I3values were still bigger, which revealed the salt-induced viscous mechanism of PSAn. At the same time, the association structure became loose, hydration size was the largest and association reached maximum, and solutions had appeared salt-thickening for the first time. When the concentration of NaCl was100g/L, absorbance A of PSA4and PSA20appeared the second peak,I1/I3values all reached minimum, besides, Ie/Im values still remained bigger, which indicated that complexation of Na+and C-O bonds in molecular branched chains strengthened intermolecular association, and formed association with a lot of big size hydrations and strong association again, therefore, the second salt-thickening appeared. In the whole concentration range of CaCl2, A values of2g/L PSA4and PSA20solutions rapidly increased to2.363and2.778respectively, and these values were higher than those in NaCl solution with the same concentration, and had continued to140g/L CaCl2, then A value increased slowly. For1.5g/L polymers PSA4and PSA20solutions in70g/L NaCl solutions within the scope of20～80℃, absorbance A and Ie/Im values all increased continuously, and I1/I3values showed irregular wave type change. Change processes of A at different temperatures of1.5g/L PSAn in140g/L CaCl2solutions were similar to those in NaCl solutions.The results of research about dynamic light scattering method showed that hydrodynamic radius (Rh) mainly distributed in single molecule area and small association area when polymers in water and30g/L NaCl solutions, and hydrodynamic radius (Rh) of0.6g/L PSA20solutions distributed in27.77-40.39nm single molecule area and180.93-263.21nm small association area.Rh distributed in30.99-57.93nm single molecule area,249-574.63nm small association area and872-1630.52nm big association area when1.2g/L polymer PSA2o in70g/L NaCl solutions. At the same PSA20concentrations, effective hydrodynamic radius in70g/L NaCl solutions were higher than in30g/L NaCl solutions and water, and hydrodynamic radius of0.5g/L polymer PSA20in70g/L and30g/L NaCl solutions and water were201.9133.7and162nm respectively. lg/L polymer PSA20in different concentrations of NaCl solutions, hydrodynamic radius of association reached maximum in70g/L NaCl solutions, resulting the largest solution viscosity. By using static light scattering and stimulation with Berry, the heavy molecular weight Mw was6.75×106g/mol, the radius of gyration (Rg) was189nm and the second virial coefficient A2was8.6×10-5cm3·mol/g2, which indicated non-linear polymer PSA2oin brine solutions had good solvation and higher gyration radius than linear HP AM with ultrahigh molecular weight. By observing the use of atomic force microscopy found that polymer PSA20in solutions formed unique rod-shaped association structure, and rod-shaped association structure became more closely and neatly with increasing polymer concentrations, which illustrated conformation stretching of molecular chain of polymer PSA20in solutions. |
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