Conventional polymers used in enhanced oil recovery (EOR) are acrylamide-based copolymers of very high molecular weight. Their viscosity in aqueous solution depends on various physicochemical parameters such as monomer composition, concentration, average molecular weight, polydispersity, salinity level and ionic composition, temperature, etc. Moreover, solutions are non-Newtonian; they exhibit low-shear Newtonian plateau viscosity at a low-shear rate followed by a shear thinning region at a higher shear rate. In the absence of a predictive model, for any new polymer grade or lot, any new or slightly varying field condition, it is necessary to perform a whole set of viscosity measurements at varying concentrations, which is tedious, time-consuming, and not valuable. Flow curves (viscosity vs shear rate) were measured on a great number of polymer solutions in various physicochemical conditions (variation of the polymer microstructure, monomer composition, molecular weight, brine salinity, and temperature). The flow curves in dilute nonentangled, semidilute nonentangled, and semidilute entangled regimes were modeled by only two adjustable parameters: the intrinsic viscosity [ η ] and the relaxation time in the dilute regime λ d. The zero-shear viscosity η 0 (more specifically, the specific viscosity η s p) and the power law index n obey master curves that are solely functions of the overlap parameter C [ η ]. The relaxation time λ depends on C [ η ] and the relaxation time in the dilute regime λ d. All these results are consistent with predictions for a neutral polymer in a good solvent. By using these master curves, intrinsic viscosity of any polymer/brine system can be easily obtained at various temperatures from a single measurement in the semidilute regime in which viscosity is higher than water, and classic rheometers are very sensitive. The whole flow curve η ( γ ˙ ) can be predicted at any concentration, temperature, and molecular weight. For any unknown polymer/brine system, the determination of λ d enables us to determine the viscosimetric average molecular weight M of the polymer. Finally, by using the additive property of the intrinsic viscosity of binary solutions, a method is proposed to evaluate the molecular weight of field samples. Polymer physics is today considered well described and well known. However, the beauty and the usefulness of this physics have been partly ignored by the EOR community up to now. This study gives a methodology to predict the viscosifying behavior and the molecular weight of any acrylamide-based copolymer/brine system. By attributing the molecular weight rather than a viscosity value, on-site and lab quality control will be greatly improved.

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用于提高石油采收率的丙烯酰胺基聚合物的普遍增粘行为

用于提高石油采收率 (EOR) 的常规聚合物是基于丙烯酰胺的分子量非常高的共聚物。它们在水溶液中的粘度取决于各种物理化学参数，如单体组成、浓度、平均分子量、多分散性、盐度水平和离子组成、温度等。此外，溶液是非牛顿的；它们在低剪切速率下表现出低剪切牛顿平台粘度，然后在较高剪切速率下出现剪切稀化区域。在没有预测模型的情况下，对于任何新的聚合物等级或批次、任何新的或略有变化的现场条件，都需要在不同浓度下进行一整套粘度测量，这是乏味、耗时且没有价值的. 在各种物理化学条件（聚合物微观结构、单体组成、分子量、盐水盐度和温度的变化）下对大量聚合物溶液测量流动曲线（粘度与剪切速率）。稀非缠结、半稀非缠结和半稀缠结体系中的流动曲线仅由两个可调参数建模：特性粘度 [ η ] 和稀体系中的弛豫时间 λ d。零剪切粘度η 0 (更具体地，比粘度η sp)和幂律指数n服从仅作为重叠参数C[η]的函数的主曲线。弛豫时间 λ 取决于 C [ η ] 和稀释状态下的弛豫时间 λ d。所有这些结果都与在良好溶剂中的中性聚合物的预测一致。通过使用这些主曲线，任何聚合物/盐水系统的特性粘度都可以在不同温度下通过在粘度高于水的半稀释状态中的单次测量轻松获得，并且经典流变仪非常灵敏。可以在任何浓度、温度和分子量下预测整个流量曲线 η ( γ ˙ )。对于任何未知的聚合物/盐水系统，λ d 的确定使我们能够确定聚合物的粘度平均分子量 M。最后，利用二元溶液特性粘度的可加性，提出了一种评估现场样品分子量的方法。聚合物物理学今天被认为是充分描述和众所周知的。然而，到目前为止，EOR 社区已经部分地忽略了这种物理的美丽和有用性。本研究提供了一种方法来预测任何基于丙烯酰胺的共聚物/盐水系统的增粘行为和分子量。通过归因于分子量而不是粘度值，现场和实验室的质量控制将得到极大改善。