Summary
Dissolution kinetics of analcime (a zeolite), chlorite, and illite (layered
aluminosilicates) are examined in hydrochloric and mixtures of hydrochloric and
hydrofluoric acid systems. Dissolution kinetics were determined from batch
reactor experiments in the temperature range of 25 to 100°C. The reaction
progress was monitored by analysis of Al, Si, Fe, Mg, and Na concentrations in
the aqueous phase. The reactivity of these aluminosilicates was compared with
that of kaolinite under similar experimental conditions.
Models for the reaction of the aluminosilicates with each acid are
presented. The reaction kinetics incorporated into a geochemical
simulator predict matrix-stimulation results for formations containing these
minerals. Guidelines for design of matrix-stimulation treatments for
acid-sensitive formations are formulated.
Introduction
Sandstone acidizing is a complex operation because the treatment involves
flow and reactions in porous media where the reactive chemicals can contact a
wide range of minerals. The formation may contain various amounts of silica
(SiO2), clays (aluminosilicates such as kaolinite or illite), or alkaline
aluminosilicates such as feldspar and zeolites, as well as calcium and
magnesium carbonates. Recent studies on matrix stimulation have strongly
emphasized the importance of secondary and tertiary reactions in determining
the success of matrix treatments (Gdanski 1996, 1997a). However, for
acid-sensitive aluminosilicates, these reactions are especially important
because they occur at much shorter time scales than for the nonacid-sensitive
minerals. The presence of acid-sensitive aluminosilicates may dominate
treatment design considerations, even though they may be present in small
quantities compared to other aluminosilicates.
Appropriate selection of treatment fluids is key in preventing formation
damage in presence of acid-sensitive aluminosilicates. However, the extent
of secondary and tertiary reactions under reservoir conditions for each fluid
and mineral is difficult to quantify with laboratory testing alone (Ziauddin et
al. 2002a). In this study, a combination of laboratory testing and geochemical
simulations have been used to elucidate the underlying reaction mechanisms for
these minerals and to determine their impact on reservoir treatments.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
24 September 2003
- Revised manuscript received:
17 August 2005
- Manuscript approved:
18 August 2005
- Version of record:
20 May 2006
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