Experimental Evidence
for Self-Limiting Reactive Flow
through a Fractured Cement Core: Implications for Time-Dependent Wellbore
Leakage
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Abstract
We present a set of reactive transport experiments in
cement fractures.
The experiments simulate coupling between flow and reaction when acidic,
CO<sub>2</sub>-rich fluids flow along a leaky wellbore. An analog
dilute acid with a pH between 2.0 and 3.15 was injected at constant
rate between 0.3 and 9.4 cm/s into a fractured cement core. Pressure
differential across the core and effluent pH were measured to track
flow path evolution, which was analyzed with electron microscopy after
injection. In many experiments reaction was restricted within relatively
narrow, tortuous channels along the fracture surface. The observations
are consistent with coupling between flow and dissolution/precipitation.
Injected acid reacts along the fracture surface to leach calcium from
cement phases. Ahead of the reaction front, high pH pore fluid mixes
with calcium-rich water and induces mineral precipitation. Increases
in the pressure differential for most experiments indicate that precipitation
can be sufficient to restrict flow. Experimental data from this study
combined with published field evidence for mineral precipitation along
cemented annuli suggests that leakage of CO<sub>2</sub>-rich fluids
along a wellbore may seal the leakage pathway if the initial aperture
is small and residence time allows mobilization and precipitation
of minerals along the fracture