1. 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.

2. 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

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

4. 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

5. Visualization of Employment

6. 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

7. 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

8. 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’?

9. 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.

10. Polymer Results

14. Temperature Effects AT-O3S

16. 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.

17. 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.

18. 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.

19. 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.

20. Literature
Al-Anazi, H.A., & Sharma, M.M. (2002). Use of a pH sensitive Polymer for Conformance Control. SPE Presented at the SPE International Symposium and Exhibition on Formation Damage Control held in Lafayette, Louisiana February 2002.
Dandekar, A.Y. Petroleum Reservoir Rock and Fluid Properties Second Edition. CRC Press Broken Sound Parkway NW, Suite 300 Boca Raton, FL. Page
Chia, P.C., Bai, B. Modeling Preformed Particle Gel Swelling and Deswelling Kinetics. Undergraduate Research, Missouri School of Technology, 20 March 2010.
Elsharafi, M.O., & Bai, B. (2015). Gel Pack-A Novel Concept to Optimize Preformed Particle Gels (PPGs) Conformance Control Treatment Design. Presented at SWPSC Conference held in Lubbock, Texas April 2015.
Elsharafi, M.O. (2015). Effect of Back Pressure on Gel Pack Permeability During Conformance Control Treatment. Presented at the 2015 Southwest Section of the AAPG Annual Convention held in Wichita Falls, Texas April 2015.
Xu, W., Ok, J.T., Xiao, F., Neeves, K.B., & Yin, X. (September 3rd, 2014). Effect of Pore Geometry and Interfacial Tension on water-oil Displacement Efficiency in oil-wet Microfluidic Porous Media Analogs. Paper, Physics of Fluids

21. Thank You! Any Questions?