New Insights Into the Viscosity of Polymer-Based In-Situ-Gelled Acids

Abstract

Diversion techniques must be employed to remove all the damage from the entire producing interval. Diversion in carbonates is more difficult than in sandstones because of the ability of acid to significantly increase the permeability in carbonates as the acid dissolves carbonate rocks. The apparent viscosity of the in-situ-gelled acid based on polymer plays a key role in diversion because it creates a viscosity differential in treated and untreated zones. An extensive literature survey and field data show that there is no agreement on the effectiveness of this acid system. Therefore, this study was conducted to better understand this acid system and determine factors that impact its viscosity buildup. Three commercially available in-situ acids were examined.The effect of salts and iron (III) [Fe(III)] contamination on the apparent viscosity of these acids was examined in detail. Several new findings were identified, including that polymer and other additives were separated out of the acid when these acids were prepared in high-salinity brines. Preparing the in-situ-gelled acid with saline waters decreased the viscosity of the acid in live and partially neutralized conditions. Concentrated hydrochloric acid (HCl) solutions produced high concentrations of calcium ion that reduced the viscosity of the in-situ-gelled acid system. Therefore, in-situ-gelled acids that are based on polymers should be used at low HCl concentrations (3 to 5 wt% HCl). Sodium (NaCl), calcium (CaCl 2 ), or ferric chloride (FeCl 3 ) reduced the apparent viscosity of live gelled acids. A brown precipitate was noted during the neutralization of acid systems that contained Fe (III), even in the presence of the recommended concentration of iron-control agents. Therefore, in-situ-gelled acids that are based on polymers should be prepared using low salinity waters and used at low HCl concentrations (3 to 5 wt% HCl).

HCl/Formic In-Situ-Gelled Acids as Diverting Agents for Carbonate Acidizing

“…The increase in the formic acid concentration is associated with a reduction in HCl concentration. However, Gomaa and Nasr El-Din (2010b) showed that changes in initial HCl concentration did not have a significant effect on the viscosity of live in-situ-gelled acids. The effect of formic and acetic acids on the viscosity of live in-situ-gelled acids was investigated by van Domelen and Jennings (1995).…”

“…The concentrations of HCl and formic acid were selected so that all acid systems had an initial acid concentration that was equivalent to 5 wt% HCl (on a molar basis). On the basis of Gomaa and Nasr El-Din (2010b), this acid concentration gave high viscosity and best diversion performance. The five acids tested had the following acid concentrations:…”

Corrosion-Inhibitor Design for Compatibility with Acid-Gelling Polymers

“…Use of lower acid strengths for acid diversion jobs has been advocated for other reasons as well. Gomaa and Nasr-El-Din (2010) recommend use of 3 to 5% HCl for polymer diversion because lesser amounts of calcium ions are released from the spending reaction of HCl on formation carbonates, and the calcium ion concentration was shown to affect apparent viscosity. A 3 to 5% HCl concentration is also used by Yeager and Shuchart (1997), but for the purpose of quicker and more-efficient diversion, especially in lower-temperature and/or less-reactive formations.…”

Propagation of Regular HCl Acids in Carbonate Rocks: The Impact of an In Situ Gelled Acid Stage

“…However, 5 wt. % HCI was recommended because of the negative effect of the reaction products (CaC^) on the apparent viscosity of polymer solutions [22]. Therefore, in this study, a 5 wt.…”