# Superabsorbent Polymer

Note: In this post, I would like to introduce the superabsorbent polymer (SAP),which could be used as conformance control agent in oil and gas field. SAPs could absorb and hold a large amount of water or aqueous solutions even under high pressure and high temperature. Just as described in the summary of my proposal, in my research, I mainly test the flow properties of SAP through the fracture or fracture-like model, and the rheological properties with rheometer. Some of the swelling and deswelling behaviors and the effects on the injectivity of SAP through fractures were investigated also. Today SAPs will be introduced in general here. Later,  The following context is modified from an unpublished paper by my advisor and me. All rights reserved.

The superabsorbent polymers (SAPs) most commonly available are hard, dry, granular or powdered products made up of a cross-linked polymer with a three dimensional network structure that absorbs and holds a large amount of water and swells up to 200 times its original size and weight in fresh water or aqueous solutions while maintaining its physical structure. [1-4] SAPs are increasingly used in multiple fields of human activity, such as biomedical, agricultural, personal care, and industrial because of its high water absorbing capability. [4-6] Recently, SAPs have been applied in conformance control and water shutoff because they have significant advantages over the bulk gels used in in situ gelling processes, such as controllable size and strength, high chemical and temperature resistance, minimum formation damage, less surface facility requirements, and environmental friendly. [7] Except for the super water absorbency, the mechanical properties of SAPs are very important to the conformance control processes, such as the strength and injectivity. Dynamic mechanical analysis (DMA), rheometry and core flooding experiments are commonly used to determine the mechanical properties. Comparing to core flooding experiments, DMA and rheometry are much more cost-effective.

The SAP used in the research is LiquiBlock™ 40K (40K), a commercial product from Emerging Technology Inc. 40K is crosslinked acrylamide/potassium acrylate copolymer and the major component is 2-Propenoic acid, potassium salt, polymer with 2-proenamide. Its molecular structure is shown in Scheme 1.

Scheme 1. The molecular structure of 2-Propenoic acid, potassium salt, polymer with 2-proenamide.

In preparation for the rheological experiments, preselected dried SAP particles between 20- and 30-mesh were dispersed in 0.05%, 0.25%, 1.00%, and 10.00% sodium chloride solutions for 24 hours to achieve the maximum swelling. Because the density of both dried SAP and swollen SAP is higher than the density of brine, the swollen SAP always precipitated at the bottom of the centrifuge cell. The original and ultimate volumes of SAP in a centrifuge cell were recorded. The swelling ratio of the SAP was calculated from the following equation:

$S_{w}=\frac{V_{s}}{V_{d}}\times 100\%$

where Vs is the volume of swollen SAP and V0 is its original volume. Table 1 shows the ultimate swelling ratios for SAPs in various concentrations of brine.

Table 1. Swelling Ratios for SAP in Brine

 Brine Conc. (%) Swelling Ratio (%) Original Dia. (mm) Swollen Dia. (mm) 0.05 20455 0.595-0.841 3.506-4.955 0.25 9659 0.595-0.841 2.730-3.859 1.00 5682 0.595-0.841 2.287-3.233 10.00 3125 0.595-0.841 1.874-2.649

REFERENCES

1. Tang, H. (ChemEOR, Inc.) U.S. USPTO 20,070,204,989

2. Bai, B.; Liu, Y.; Coste, J.-P.; Li, L. SPE Res Eval & Eng 2007, 10, 415-422.

3. Das, M.; Zhang, H.; Kumacheva, E. Annu. Rev. Mater. Res. 2006, 36, 117-144.

4. Buchholz, F. L.; Graham, A. T. In Modern Superabsorbent Polymer Technology; John, Wiley & Sons, Inc.: New York, 1997; chapter 1, 7, pp 22.

5. Raju, K. M.; Raju, M. P.; Mohan, Y. M. Polym. Int. 2003, 52, 768-772.

6. Samchenko, Y. M.; Ul’berg, Z. R.; Komarskii, S. A. Colloid J. 2004, 66, 350-354.

7. Liu, Y.; Bai, B.; Wang, Y. Oil Gas Sci. Technol. – Rev. IFP. 2010. http://ogst.ifp.fr/index.php?option=article&access=standard&Itemid=129&url=/articles/ogst/pdf/first/ogst09046.pdf