Summary
Surfactant-based acids have been used for diversion because they are less
damaging to the formation. Amphoteric viscoelastic surfactant (VES) is the main
type of surfactant being used today. Low viscosity is observed in the live-acid
systems, whereas significantly increased viscosity is found when HCl reacts
with carbonate and generates divalent salts. The surfactant/acid system can be
broken after acid treatments by mixing with reservoir hydrocarbons, or by using
an external or internal breaker.
Amidoamine oxide, an amphoteric surfactant, was examined in this work. The
prepared surfactant-based live-acid system contained 20 wt% HCl, 4 wt%
surfactant, and 1 wt% corrosion inhibitor. Different organic acids/chelating
agents were added to live and spent acids. Calcium carbonate particles were
used to neutralize live acids. The objective was to examine how these organic
acids/chelating agents affected the rheological properties of spent-acid
systems. Measurements were made at temperatures from 75 to 200°F at a shear
rate of 10 sec-1 and a pressure of 300 psi. Several simple organic
acids (formic, acetic, propionic, and butyric) and chelating agents [glycolic
acid, lactic acid, gluconic acid, citric acid, tetrasodium ethylenediamine
tetraacetic acid (EDTA), tetrasodium L-glutamic acid, N, N-diacetic acid
(GLDA), and disodium L-glutamic acid, N, N-diacetic acid (HEIDA)] that are used
in the field were examined.
Experimental results indicated that the addition of simple organic acids or
chelating agents reduced the viscosity of spent acids significantly. This
reduction in viscosity increased with the number of carbon atoms in the organic
acid. The addition of organic acids reduced the temperature range in which the
surfactant can be used. Chelating agents (α-hydroxy carboxylic acids and
amino carboxylic acids) also tended to break the surfactant gel if enough
chelant was used. On the basis of the results obtained, organic acids can be
used to break surfactant gel. Transmission electron microscopy (TEM) tests were
first conducted to examine how organic acids/chelating agents interfered with
the formation of rod-like micelles in the surfactant-based acid. The results
showed that the addition of organic acids to the spent acid generated a fewer
elongated micelles and resulted in less apparent viscosity. In addition, if
chelating agents or simple organic acids are used, then the concentration of
the surfactant should be increased to compensate for the loss of viscosity
induced by the addition of the organic acids.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
20 November 2009
- Meeting paper published:
10 February 2010
- Revised manuscript received:
26 March 2010
- Manuscript approved:
14 July 2010
- Published online:
30 November 2010
- Version of record:
22 February 2011
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