Carbonate Acidizing: The Effect of Corrosion Inhibitor and Emulsion Preventer on Pore Volume to Breakthrough

TL;DR

This study shows that additives in hydrochloric acid used for carbonate rock stimulation improve reaction control and wormhole formation efficiency.

Contribution

The study demonstrates that corrosion inhibitors and emulsion preventers significantly affect acid-rock reaction kinetics and wormhole formation in carbonate acidizing.

Findings

Additives reduced pore volume to breakthrough (PVbt) values at low flow rates, indicating improved wormhole formation efficiency.

The presence of additives decreased optimal interstitial velocity by 77%, suggesting better reaction control.

Micro-CT images confirmed dominant wormhole formation with additives, while samples without additives collapsed before breakthrough.

Abstract

Acid stimulation of carbonate rocks aims to create channels
within
the rock, known as wormholes, to restore or enhance permeability,
increasing production. Among the acids used in this type of treatment,
15 wt % hydrochloric acid (HCl) stands out due to its high reactivity,
formation of soluble reaction products in aqueous media, and cost-effectiveness.
To minimize corrosion of metallic structures and avoid emulsion formation
after contact with formation oil, acid solutions are commonly prepared
with additives such as corrosion inhibitors and emulsion preventers.
To evaluate the influence of these additives on wormhole formation,
this study performed core flooding experiments at different injection
rates to construct pore volume to breakthrough (PVbt) curves,
both in the presence and absence of these additives. The tests employed
15 wt % HCl solutions, with and without additives, using Indiana Limestone
rocks containing 98.57% calcite. The experiments were conducted in
a core flooding system under an injection rate range of 0.25–16
mL/min, at 25 °C, with a confining pressure of 2000 psi and back
pressure of 1200 psi. After the tests, the cores were analyzed by
X-ray microcomputed tomography to evaluate wormhole formation. The
results indicated that additives reduced PVbt values at
low flow rates, suggesting slower reaction kinetics and higher wormhole
formation efficiency. The presence of additives decreased the optimal
interstitial velocity by approximately 77% (from 0.91 to 0.21 cm/min),
indicating that they provide better reaction control and enhance treatment
efficiency. Moreover, micro-CT images confirmed the formation of dominant
wormholes at almost all flow rates in the presence of additives, whereas
in their absence (e.g., at 0.5 mL/min), the sample collapsed before
breakthrough. The Buijse–Glasbergen model provided a good fit
to the experimental data (R
2 = 0.99) for
the additive-free curve. For the additive-containing system, however,
an empirical adjustment of the model exponent was required to improve
the correlation (from R
2 = 0.85 to R
2 = 0.93). The results demonstrate that these
additives not only inhibit corrosion and prevent emulsions but also
controlled the reactivity effect. This behavior significantly broadens
the scope of their application, reinforcing their strategic importance
in carbonate reservoir treatments.

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