Water-Insoluble Residue Following Acid Hydrolysis of Water-Soluble Polysaccharides
Authors: Pober Kenneth W. , Hoff Michael H. , Darlington R. Keith 
Published: December 2007

Summary
This paper illustrates a detailed procedure to determine acid-insoluble polymer residue. The procedure is quantitative and reproducible. Several water-soluble polymers have been evaluated by this procedure. Values polymers have been evaluated by this procedure. Values for insoluble residues at various hydrolysis times and temperatures for some common oilfield polymers are given. The insoluble residue content varies with the procedure used to do the polymer hydrolysis. During the procedure used to do the polymer hydrolysis. During the hydrolysis reaction, the insoluble residue from a cellulosic polymer goes through a minimum, then increases depending on hydrolysis time, temperature, and acid strength.

Introduction
The use of water-soluble polymers is a common practice in drilling operations, completion, workover, and production of oil and gas. After they have performed as production of oil and gas. After they have performed as required, water-soluble polymers are often acid-hydrolyzed to "break" solution viscosity or to remove the polymer as in a filter cake. Water-soluble polysaccharides are degraded in acidic media to a water-soluble polysaccharides are degraded in acidic media to a water-soluble fraction and an insoluble residue. This insoluble residue is a concern in oil and gas operations because of the potential to cause formation damage. Laboratory tests potential to cause formation damage. Laboratory tests with sandstone cores have shown that some polymer-mediated damage is temporary and reversible with acid polymer-mediated damage is temporary and reversible with acid treatment. The degree to which the damage is reversible is a function of the extent of acid degradation of the polymer and the amount of insoluble polymer residue. polymer and the amount of insoluble polymer residue. Our intention was to compare our laboratory results on percent insoluble residue with other reports in the percent insoluble residue with other reports in the literature. A literature survey for a method of determining insoluble residues from polymers upon acid hydrolysis revealed no detailed, definitive procedure. This procedure probably falls into the "everybody knows how to do it" category. Apparently, various methods are practiced, but with no published procedure, there is no basis for a uniform comparison of results. An illustration follows. Various authors have reported guar gum tocontain insoluble residues ranging from 3 to 12wt%. Polymers vary in behavior to aciddegradation. Hydrolysis time and temperatureaffect the degree to which polymers aredegraded and, hence, the amount of detectableinsoluble residue. Mahajan and Barronreported insoluble residues for severalpolymers, by hydrolysis in 15 % HCl. Their investigation, however, was limited to a singlehydrolysis time and temperature, and details oftheir procedure were not reported. In view ofthese findings, our objective then became two fold:to develop a simple acidhydrolysis procedure for determining insolubleresidue, andto evaluate a variety of oilfieldpolymers by this method.

Experimental
The procedure developed calls for common laboratory equipment, Millipore (TM) apparatus, and care in handling filter packs throughout the process, Complete details for the acid hydrolysis procedure are presented in the Appendix.
JPT
P. 2185