Summary
Emulsified acid (30 vol% diesel and 70 vol% HCl) has been used in both
matrix and acid fracturing treatments. Injecting the acid in this form has
several advantages including retarding the reaction of the acid with rock,
reducing corrosion to well tubulars, and minimizing acid additives. However,
using this acid to treat wells with asphaltene deposition requires removing
asphaltene first using a suitable aromatic-based solvent, and then using a
matrix acid treatment. This additional step increases the cost and time needed
to execute acid treatments.
To remove asphaltene deposition and enhance well productivity, hydrochloric
acid was emulsified in xylene. Xylene was the external phase, and was used to
dissolve asphaltenes. Then the acid as the dispersed phase dissolved the
carbonate rock, enhancing well productivity. Extensive laboratory work was
performed to ensure the stability of acid-in-xylene emulsion and measure its
apparent viscosity. Acid concentration was 15 wt% HCl, the acid volume fraction
was 0.7, and the balance was xylene with demulsifier. All tests were conducted
at room temperature and 160°F (bottomhole temperature).
The stability and apparent viscosity of emulsified acids were found to be a
function of the type of hydrocarbon phase used to prepare the emulsified acid.
Emulsified acids prepared with xylene had a lower apparent viscosity and were
stable for relatively shorter times. A matrix acid treatment based on
xylene-emulsified acid was applied in four wells without encountering
operational problems. Unlike previous matrix acid treatments using regular
acids, the four wells responded to the new treatment without increasing water
cut, except in one well that was wet before the treatment.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
11 August 2008
- Meeting paper published:
11 October 2008
- Revised manuscript received:
6 March 2009
- Manuscript approved:
28 June 2009
- Published online:
30 November 2009
- Version of record:
11 May 2010
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