Kinetics of a Super-Absorbent Polymer Cody Chancellor & Connor Kirby Dr. Mahmoud Elsharafi & Dr. Jeong Tae Ok McCoy School of Engineering, Midwestern State University Wichita Falls, TX 76308, USA 2016 SPE Southwestern North America Student Paper Contest on April 2, The University of Texas at Austin, TX.

What are Superabsorbent Polymers? Sodium polyacrylate, polyacrylic acid Swells when exposed to water by absorbing it. Swells to a certain ratio which is affected by various factors. Salinity of the brine Temperature of the brine pH of the brine

After exposure to DI water Dry, unswelled polymer After exposure to DI water

Use of a Superabsorbent Polymer Oil industry uses it to control water flow in oil reservoirs Reduces differences in reservoir permeability Injected into reservoir with a brine Swells and enters high permeability zone Effects on low permeability zone negligible

Visualization of Employment

Conditions in a Reservoir Salinity Sodium ions make up the majority of reservoir salinity. Calcium ions make up the second largest percentage. Other cations, like Magnesium+2 and Potassium+1, are also present. pH varies based on previous extraction operations and the contents of the in formation brine. Temperature Can range from ~0°C to upwards of 100°C

How do These Affect the Polymer? Salinity Calcium ions Divalent cations react catastrophically with the polymer’s Sodium crosslinker Precipitates out of solution with polymer as Calcium polyacrylate Sodium ions A larger concentration of Sodium ions results in a lower swelling ratio and stronger polymer pH A decrease in pH generally translates to a decrease in swelling ratio An increase in pH increases the effects of Calcium on the polymer Temperature Swelling ratio drops as temperature increases Temperature increases the effects of Calcium on the polymer

What can be Done for Calcium? ‘Preflush’ the reservoir This technique cannot be relied upon to remove all traces of Calcium from the reservoir. How severe are the effects of precipitation? What about an ‘acid wash’?

Methodology A brine consisting of Sodium Chloride and/or Calcium Chloride and deionized water was mixed by percent weight A specific amount of polymer was weighed out by a percentage of the solution. (the polymer’s weight was not included in the solution weight) When pH was adjusted, it was done by adding drops of 0.1N or 6N HCl. The brine was added on top of the polymer in a centrifuge tube The solution was agitated for 40 seconds. The solution was allowed to settle for 20 seconds. A reading was taken and the agitation step was repeated. Temperature was adjusted using preswollen samples in a bath heater.

Polymer Results

Temperature Effects AT-O3S

Discussion Mixed brines still experienced significant precipitation especially in deswelling. Once the percent change between the peak and final volumes is considered, there is clearly a decrease in precipitation as pH drops. pH is a major factor in the precipitation of the polymer at low salinities. Temperature caused significant deswelling in pH values above about 1.5 (~15%-30%). At lower pHs, the swelling ratios actually increased.

Conclusion Mixed brines appeared to have a much lower maximum swelling ratio when compared to CaCl2 only brines with the same concentration. pH has a significant inhibiting effect on the precipitation reaction of the Calcium and the polymer at low Calcium concentrations. The precipitation effect has not been fully prevented, but polymer losses have been greatly reduced in brines containing Calcium Chloride. Greater temperatures cause further precipitation in all but the most acidic solutions.

Recommendations Industry The use of a preflush to drop the concentration of divalent cations. The use of an acid wash to reduce the precipitation of polymer with small amounts of remaining divalent cations. Use a larger amount of polymer in reservoirs containing divalent cations.

Acknowledgements We would like to thank our mentors, Dr. Elsharafi and Dr. Ok from the McCoy School of Engineering, for providing this opportunity to us. We would like to thank the EURECA program and Dr. Rincon-Zachary for their generous financial support of our research. We would like to thank the McCoy School of Engineering for providing us with lab space and equipment. The Midwestern State University Chemistry Department was a great help, both in providing supplies and expertise, especially regarding the reaction between the polymer and Calcium.

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