SPE Production & Operations
Volume 25, Number 3, August 2010, pp. 367-375

SPE-121728-PA

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

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DOI  More information 10.2118/121728-PA http://dx.doi.org/10.2118/121728-PA

Citation

  • Gomaa, A.M. and Nasr-El-Din, H.A. 2010. New Insights Into the Viscosity of Polymer-Based In-Situ-Gelled Acids. SPE Prod & Oper  25 (3): 367-375. SPE-121728-PA. doi: 10.2118/121728-PA.

Discipline Categories

  • 5.5.3 Chemical Treatments
  • 5.5.4 Rock/Fluid Interactions
  • 5.3.4 Acidizing

Keywords

  • diversion, gelled acids

Summary

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 (CaCl2), or ferric chloride (FeCl3) 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).

© 2010. Society of Petroleum Engineers

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History

  • Original manuscript received: 28 February 2009
  • Meeting paper published: 21 April 2009
  • Revised manuscript received: 23 December 2009
  • Manuscript approved: 25 February 2010
  • Published online: 8 July 2010
  • Version of record: 11 August 2010