部分水解聚丙烯酰胺驱油过程中机械降解研究——分子量、粘度及相关参数的变化

Studies on Mechanical Degradation of Partially Hydrolized Polyacrylamide in Course of Polymer Flooding: Changes in Relative Molecular Mass, Viscosity and Related Parameters

以单分散PAM为标样,1mol/LNaCl水溶液为溶剂,用GPC-LS联合技术在25℃测定了水解度25.0%的驱油聚合物HPAM的分子链远程结构参数。HPAM在新配溶液中,〈M〉n和〈M〉w分别为4.672×106和4.820×106,开始聚合物驱2年、4年、6年后采出液中分别降至原值的12.6%和19.0%,18.4%和24.9%,20.2%和22.2%;均方回转半径值的变化相似。1000mg/L的HPAM清水溶液在45℃受剪切后,〈M〉n和〈M〉w随剪切速率和剪切时间增加而下降,5000s-1和3min时降至最小,为原值的25%左右。HPAM溶液流经2.0μm2岩心后,粘度(45℃,7.34s-1)和〈M〉w随注入流量增加而持续下降,粘度在流量20mL/min(2747s-1)时下降至原值的20.8%,〈M〉w在流量大于1mL/min(137s-1)后迅速下降,5mL/min(687s-1)时下降至原值的1/3以下,此后下降趋缓;粘度和〈M〉w在岩心渗透率为2.0,1.0μm2时下降较缓,为0.45,0.25μm2时下降剧烈。用地层水配制的溶液在45℃放置5天,HPAM的〈M〉n基本不变,〈M〉w轻度下降。结论:HPAM发生降解的主要原因是HPAM通过油层孔隙孔喉时高分子链受到剪切和拉伸共同作用而断裂;岩心内的降解与注入流量密切相关,临界流量是1mL/min(相当于175s-1);化学降解等不是主要因素。图7表2参19。

The long-range chain structural parameters of HPAM for EOR are measured at 25℃by using GPC-light scattering combinational technique with a monodispesity PAM standard sample and 0.1 mol/L NaCl aqueous solution as solvent. The values of 〈M〉nand〈M〉wof HPAM measured are of 4. 672×106and 4. 820×106in the original solution and are decreased down to 12. 6% and 19. 0%, 18. 4% and 24. 9%, and 20. 2% and 22. 2% of their initial values in the waters produced in 2,4 and 6 years after starting polymer flood, respectively; similar changes are observed in measurements of mean square gyration radius of polymer coils. After 1000 mg/L HPAM solution in fresh water having been sheared at 45℃, the〈M〉nand〈M〉wmeasured decrease with increasing shear rate or shearing time to lowest values, about 25% of their initial values, at 5000 s-1over 3 minutes. For the HPAM solution flown through cores of 2. 0μm2, the viscosity (at 45℃and 7. 34 s-1) and the〈M〉wdecrease continuously with increasing injecting flowing rate (FR): the viscosity is decreased to 20. 8% of its initial value at FR 20 mL/min (2747 s-1) and the〈M〉w decreases fast at FR>1 mL/min (137 s-1) and slow at >5 mL/min (687 s-1) and reaches <1/3 of its initial value at 5 mL/min; the viscosity and〈M〉wdecrease with increasing FR moderately in cores of permeability 2. 0 and 1. 0μm2and dramatically in cores of 0. 45 and 0. 25μm2. In formation water solution the〈M〉nof HPAM practically does not change and its〈M〉wslightly decreases when the solution is let stand at 45℃over 5 days. It is concluded that: the degradation of HPAM occurs mainly by the joint action of shear and tensile forces upon polymer chains in pore throats of reservoir strata; the degradation of HPAM in cores is closely related to FR with critical FR being of 1 mL/min, or a critical shear rate of 175 s-1; the chemical and other degradation may not be an important factor.