Development of Reacted Channel During Flow of CO2 Rich Water Along a Cement Fracture

AbstractLab scale experiments were performed to characterize how coupling between reaction and flow affect time-dependent flux of CO2-rich water along leaky wells. The core flow system applies confining stress to a cement core with a single tensile fracture while CO2-rich water is injected at constant rate and elevated pore pressure. Results show no significant variation in pressure differential, despite the development of a texturally distinct calcium depleted channel along the fracture surfaces which is bounded by thin rims of precipitation. Silicon rich material remains in the channel and prevents wormhole development and large increases in aperture. Implications for time-dependent CO2 leakage are that even with high fluid flux, the leak does not get appreciably worse

Experimental Evidence for Self-Limiting Reactive Flow through a Fractured Cement Core: Implications for Time-Dependent Wellbore Leakage

We present a set of reactive transport experiments in cement fractures. The experiments simulate coupling between flow and reaction when acidic, CO₂-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 CO₂-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