1. 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

2. 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

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

8. 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?

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 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.

10. Polymer Results

14. 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.

15. 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.

16. 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.

17. 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

18. Thank You! Any Questions?