Polymer flooding is a widely employed Enhanced Oil Recovery (EOR) technique, aimed at improving sweep efficiency and maximizing hydrocarbon recovery. Accurate monitoring of polymer concentration in production fluids is essential for optimizing EOR operations and assessing reservoir performance. However, the presence of contaminants, such as solid particles, oil droplets, and other contaminants makes polymer concentration determination quite challenging on production side.

Main limitations of current quantification techniques are summarized below:

  • The bleach method might not be applicable to polymers containing 10% to 25 mol% or more ATBS and suffers from interferences with divalent cations.

  • The chemical oxygen demand method is sensitive to chloride content limiting its application to low salinity water. It also suffers interferences from oil contamination.

  • Refractometry requires stable water composition, free of oil.

  • Time resolve fluorescence is sensitive to salinity fluctuations and presence of oil contaminants.

These methods are also sensitive to variation of chemical composition of the polymer such as an increase of its hydrolysis degree during propagation through the reservoir.

This paper presents the results of the first field implementation of a robust analytical approach utilizing Size Exclusion Chromatography (SEC) coupled with a Refractive Index Detector (RID) to determine polymer concentrations in oilfield production fluids from the UNLF polymer flooding pilot in Kuwait.

The following protocol was implemented:

  1. Production fluid samples were submitted to a pre-treatment step consisting in reducing Mw distribution to a specific and controlled lower Mw distribution before being diluted in the brine used as mobile phase for the SEC device.

  2. The polymer-containing solution was injected into the SEC columns and separated from the smaller impurities.

  3. The eluted fractions from the SEC column were directed to the RI detector measuring changes in refractive index as molecules pass through. RID signal was converted into polymer concentration using a calibration curve.

Results showed that SEC effectively separates polymer from contaminants, eliminating the need for extensive sample pre-treatment and providing a direct measurement of polymer concentration even in complex matrix. The calibration curve generated with known polymer standards ensures accurate and quantitative results. The SEC-RID is not affected by the polymer chemical composition, making it compatible with any EOR polymer and unsensitive to potential increase in hydrolysis degree through the reservoir. The system was used to adjust the parameter of the pilot maximizing project performances.

Size Exclusion Chromatography coupled with a Refractive Index Detector offers a reliable and universal method for determining polymer concentrations in oilfield production fluids during polymer flooding. It selectively quantifies polymer while excluding interfering contaminants, making it an invaluable tool for optimizing EOR processes and assessing reservoir performance. Incorporating this technique into oilfield monitoring practices improves the efficiency and sustainability of polymer flooding operations.

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