Evaluate the Effect of pH on the Mixed Brine and Chemical Solutions Cody Chancellor Dr. Mahmoud Elsharafi McCoy School of Engineering, Midwestern State University Wichita Falls, TX 76308, USA 2016 NTASC at Midwestern State University Wichita Falls, TX

What are Superabsorbent Polymers? 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 Sodium polyacrylate, polyacrylic acid 35-60 mesh Inverse Polymer Suspension

After exposure to DI water Dry, unswollen 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 increases as temperature increases Temperature increases the effects of Calcium on the polymer

What can be Done for Calcium? ‘Preflush’ the reservoir This technique is not always effective. How severe are the effects of precipitation in mixed brines? How does pH affect this?

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 HCl. The brine was added on top of the polymer in a centrifuge tube The solution was agitated The solution was allowed to settle A reading was taken and the agitation step was repeated.

Polymer Results

Discussion Mixed brines were relatively unaffected until a pH below 1 was attained. Brines of only Calcium Chloride saw decreases over a larger pH range. pH is a factor in the precipitation of the polymer at low salinities, even in mixed brines. pH has a greater effect on Calcium Chloride brines than mixed brines.

Conclusion Dropping reservoir pH during an SAP treatment could be effective at preventing precipitation 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 in all cases, but polymer losses have been greatly reduced in brines containing Calcium Chloride. The dampening effect of Sodium ions on polymer swelling may play a role in decreasing pH effects over larger range.

Acknowledgements We would like to thank our mentor, Dr. Elsharafi 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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