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

在加拿大，化学驱目前正在应用于阿尔伯塔省东南部、萨斯喀彻温省西南部和劳埃德明斯特地区的一些中稠油油藏，以提高采收率。在cEOR作业中，将化学物质注入井中以提高采收率，但不同的油藏作业条件（例如pH、温度、盐度、碱和/或表面活性剂的存在）会影响聚合物的结构和尺寸。聚合物结构或尺寸的变化最终会影响到采收率的提高、项目的经济效益，也会给后采出水中聚合物的准确检测和表征带来困难（因此也会影响到聚合物的最佳再利用）。

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.