Wormhole formation and compact dissolution in single- and two-phase CO2-brine injections

Injection of acids and CO2 into geologic formations leads to dissolution of soluble minerals comprising reservoirs rocks. This increases the uncertainty in predicting the security and injectivity of geologic CO2 storage. Here through time-lapse computed tomography of injection experiments, we present the first dynamic data on wormhole formation and the fluid flow therein. We show that the dissolution during single-phase flow produces wormholes, as found previously, but that two-phase flow during CO2-brine injection leads to compact dissolution. The latter is explained by CO2 preferentially occupying wormhole seeds, which prevents their growth as CO2 is less reactive than acidic brine. On the other hand, the wormhole seeds continue to grow under single-phase flows with only acidic fluid. The results also suggest that initial Peclet and Damkohler numbers for the single-phase flow process would fail to describe the dynamic process of whether compact or wormhole dissolution would ensue.