Characterization of Ultra-High Molecular Weight Oilfield Polymers for Optimal Chemical Enhanced Oil Recovery Performance and Reuse of Produced Water

在加拿大，目前正在实施化学驱油，以提高阿尔伯塔省东南部、萨斯喀彻温省西南部和劳埃德明斯特地区一些中稠油油藏的采收率。在三次采油作业中，将化学剂注入油井以提高采收率，但不同的油藏操作条件(例如，pH、温度、盐度以及碱和/或表面活性剂的存在)会影响聚合物的结构和大小。聚合物结构或尺寸的变化最终会损害增量采油性能和项目经济性，也会导致在回采水中准确检测和表征聚合物(从而实现最佳再利用)的难度。 因此，用于cEOR的各种类型的超高摩尔质量聚合物需要准确地描述聚合物的摩尔质量和流体力学尺寸，以便进行最佳设计。目前油田聚合物表征方法仅限于用特性黏度测定聚合物的相对分子质量。由于各种原因，光散射或显微镜、SEC、紫外可见测量和液相色谱等技术不能准确地研究这些大分子的复杂结构。此外，聚合物的筛选主要依赖于本体的流变性，而拉伸流变学的作用还不是很清楚。由于聚合物溶液可能具有明显不同的剪切和拉伸行为，因此对拉伸数据的有限了解可能导致为给定的cEOR项目选择高度误导性的化学品。 为了克服这些挑战，这项工作将集中在以下前沿研究：1)不同油藏环境下注入聚合物的尺寸和分子结构表征；2)开发用于检测和表征回采聚合物的方法；3)测量用于开发最佳三元复合驱段塞的cEOR化学相互作用；4)拉伸流变特性及其在cEOR性能中的作用；5)开发一个可信的数据库，用于模拟化学在多孔介质中的流动。将研究几个参数(如pH、离子强度、温度和其他反应物混合比)对分子尺寸、摩尔质量、摩尔质量分布和聚集体形成的影响。了解这些对聚合物结构和尺寸的影响将有助于更有效地设计cEOR工艺。在第二阶段的研究中，将使用毛细管破裂延伸菱形仪来测试不同油藏环境下各种COOR化学剂的毛细管破碎和伸长特性。粘弹性聚合物的毛细管稀化和破碎过程的动力学以及聚合物的尺寸和结构表征将用于寻找/设计最佳的化学段塞。

In Canada, chemical flooding is currently being applied to increase recovery from a number of medium to heavy oil pools in southeast Alberta, southwest Saskatchewan and in the Lloydminster region. In cEOR operations, chemicals are injected into wells to increase oil recovery, but different reservoir operating conditions (e.g. pH, temperature, salinity and presence of alkali and/or surfactant) affect polymer structure and size. Changes in polymer structure or size ultimately compromise the incremental oil recovery performance, project economics, and also contribute to difficulties in its accurate detection and characterization in back produced water (and therefore its optimal reuse). Therefore, various types of ultra-high molar mass polymers used in cEOR require an accurate description of polymer molar mass and hydrodynamic size for their optimal design. The present methods of oilfield polymer characterizations are limited to intrinsic viscosity measurement for molecular weight determination. The techniques, such as light scattering or microscopy, SEC, ultraviolet visible measurements and liquid chromatography, are not capable of accurately investigating these macromolecular complex structures for various reasons. Moreover, screening and selection procedure of polymers for cEOR are mainly relies on bulk rheological properties, while the role of extensional rheology is not well understood. Since polymer solutions can have markedly different shear and extensional behaviours, the limited knowledge of extensional data can lead to a highly misleading selection of chemicals for a given cEOR project. To overcome these challenges, this work will be focused on following cutting edge research: 1) Injected polymer size and molecular structure characterization under different reservoir environment, 2) Developing method for detection and characterization of back produced cEOR polymers, 3) Measurements of cEOR chemical interaction for development of an optimal ASP slug, 4) Extensional rheological characterization and its role in cEOR performance, 5) Developing a credible database for modelling chemical flow through porous media. The effect of several parameters (e.g. pH, ionic strength, temperature and other reactant mixing ratios) on the molecular sizes, molar masses, molar mass distribution, and the formation of aggregates will be studied. Understanding these effects on polymer structure and size will enable the more efficient design of cEOR process. For the second phase of the research, the capillary breakup extensional rhometer will be used to examine the capillary breakup and elongation properties of various cEOR chemicals for different reservoir environments. The dynamics of the capillary thinning and breakup process for viscoelastic cEOR polymers together with polymer size and structure characterization will be used to find/design the best suitable chemical slug.