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

在加拿大，化学驱油目前正用于提高阿尔伯塔东南部、萨斯喀彻温西南部和阿尔伯塔地区一些中到稠油油藏的采收率。在cEOR操作中，将化学品注入威尔斯井中以提高油采收率，但不同的储层操作条件（例如pH、温度、盐度和碱和/或表面活性剂的存在）影响聚合物结构和尺寸。聚合物结构或尺寸的变化最终会损害增加的石油采收率性能、项目经济性，并且还导致难以在回采水中准确检测和表征聚合物（因此难以实现其最佳再利用）。因此，cEOR中使用的各种类型的超高摩尔质量聚合物需要精确描述聚合物摩尔质量和流体动力学尺寸，以便进行优化设计。目前的油田聚合物表征方法仅限于测定特性粘度来确定分子量。由于各种原因，诸如光散射或显微镜、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复合物的结构。此外，用于cEOR的聚合物的筛选和选择程序主要依赖于本体流变学性质，而拉伸流变学的作用还没有得到很好的理解。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对给定cEOR项目的化学品的高度误导性选择。为了克服这些挑战，这项工作将侧重于以下前沿研究：1）在不同储层环境下注入的聚合物尺寸和分子结构表征，2）开发用于检测和表征回产cEOR聚合物的方法，3）测量cEOR化学相互作用以开发最佳ASP段塞，4）延伸流变表征及其在cEOR性能中的作用，5）开发用于模拟通过多孔介质的化学流动的可靠数据库。将研究几个参数（例如pH、离子强度、温度和其他反应物混合比）对分子大小、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使cEOR工艺的设计更加有效。在研究的第二阶段，将使用毛细管破裂延伸流变仪来检查不同储层环境的各种cEOR化学品的毛细管破裂和延伸特性。粘弹性cEOR聚合物的毛细管变薄和破裂过程的动力学以及聚合物尺寸和结构表征将用于寻找/设计最合适的化学段塞。**

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.**