Summary
Matrix acidizing is used in carbonate formations to create wormholes that
connect the formation to the wellbore. Hydrochloric acid (HCl), organic acids,
or mixtures of these acids are typically used in matrix-acidizing treatments of
carbonate reservoirs. However, the use of these acids in deep wells has some
major drawbacks, including high and uncontrolled reaction rates and corrosion
to well tubulars, especially those made of chromium-based tubulars (Cr-13 and
duplex steel); and these problems become severe at high temperatures. To
overcome problems associated with strong acids, chelating agents were
introduced and used in the field. However, major concerns with most of these
chemicals are their limited dissolving power and negative environmental
impact.
L-glutamic acid diacetic acid (GLDA), a newly developed environmentally
friendly chelate, was examined as a replacement for acid treatments in deep oil
and gas wells. The solubility of calcium carbonate (CaCO3) in the
new chelate was measured over a wide range of parameters. Coreflood tests were
conducted using long Indiana limestone cores 1.5 in. in diameter and 20 in. in
length, which allowed better understanding of the propagation of this chemical
in carbonate rocks. The cores were X-ray scanned before and after the injection
of chelate solutions into the cores. The concentration of calcium (Ca) and
chelate was measured in the core effluent samples. To the best of our
knowledge, this is the first study to examine the fate and propagation of
chelating agents in coreflood studies.
GLDA has a very good ability to dissolve Ca from carbonate rocks over a wide
pH range by a combination of acid dissolution and chelation. The addition of 5
wt% sodium chloride (NaCl) did not affect the GLDA performance at pH = 13 but
significantly accelerated the reaction at pH = 1.7. Compared with other
chelating agents, GLDA dissolved more Ca than ethanoldiglycinic acid (EDG) but
less than hydroxyethyl ethylenediamine triacetic acid (HEDTA) at high pH
values. GLDA of pH = 1.7 was able to form wormholes at 2 and 3
cm3/min. GLDA was found to be thermally stable at temperatures up to
350°F.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
18 November 2009
- Meeting paper published:
26 October 2010
- Revised manuscript received:
20 April 2010
- Manuscript approved:
24 August 2010
- Published online:
31 March 2011
- Version of record:
15 September 2011
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