Field Techniques for Accurate Back Produced Polymer Quantification for Enhanced Oil Recovery Projects
Authors: Renta D. V. , De Vita A. G. , Diaz Toro P. C. , Terra N. , Metidji M. Ould 
Published: April 2024

Accurate quantification of polymer content plays a key role in the success of polymer flooding projects, encompassing both the injection side and the production side. Lately, the focus on monitoring polymer concentration in produced water has intensified due to its potential implications for water treatment challenges. These include the formation of tighter emulsions, heater fouling, incompatibilities with other chemical products, among others. If left unaddressed, these factors can significantly impact the economics of Enhanced Oil Recovery (EOR) projects.

To mitigate these issues effectively, obtaining precise information about polymer concentration in produced fluids is imperative. Such data enables us to comprehend and forecast the impact on water treatment facilities, enabling a proactive strategy for optimizing water treatment and reinjection. Furthermore, understanding the quantity of polymer produced from each well serves as a valuable tool for gaining insights into reservoir behavior and project responses, functioning as a "tracer" for analysis.

This paper presents a comprehensive study of diverse techniques for the field-level monitoring of polymer concentration in produced water. The goal was to identify the most suitable method for each project, considering simplicity, cost, implementation, and accuracy. Normally, due to the advantages in terms of cost and simplicity, the most used method is bleach, but when this technique coul dn't be applied, other methods were evaluated.

The methods examined were bleach, starch iodide, chemical oxygen demand (COD) and size exclusion chromatography (SEC), with SEC serving as the reference or "universal" method. To achieve this goal, extensive analyses were conducted on several samples collected from a variety of global projects. These analyses provided valuable insights into the applicability of these methods in terms of accuracy, variability, and limitations. The results unveiled the following fundamental findings: Bleach method can systematically overestimate polymer concentrations, showing significant interference from sample color. The lack of a representative blank sample can also lead to an overestimation of polymer content introducing errors in the results depending on the matrix. Additionally, this method didn't allow to monitor polymers with 25% of acrylamide tertiary butyl sulfonic acid (ATBS). This could be explained by the polymer chemistry, not being possible to develop turbidity due to the ATBS functional groups.The COD method, while suitable in clean samples, showed significant differences compared to the reference method even after pre-treatment. Since it is not a polymer selective technique, it can overestimate polymer concentration by also measuring the rest of organic matter present in the sample.Starch-iodide can provide good estimations of polymer concentration, but it can also underestimate polymer content which could be explained on the chemical side by the potential hydrolysis suffered by the polymer during its passage through the reservoir.

In conclusion, it is evident that there is no universal method for measuring polymer concentration in production water. Instead, a case- by-case study must be conducted, considering factors such as applicability, costs, and required precision. Each method must be carefully evaluated to ensure its suitability for the specific context, thereby enabling accurate and cost-effective polymer quantification in production water. This study aims to contribute valuable insights into the selection and application of polymer concentration monitoring methods in EOR projects.