Surface-Volume Scaling Controlled by Dissolution Regimes in a Multiphase Flow Environment

Fluid-rock dissolution occurs ubiquitously in geological systems. Surface-volume scaling is central to predicting overall dissolution rate R involved in modeling dissolution processes. Previous works focused on single-phase environments but overlooked the multiphase-flow effect. Here, through limestone-based microfluidics experiments, we establish a fundamental link between dissolution regimes and scaling laws. In regime I (uniform), the scaling is consistent with classic law, and a satisfactory prediction of R can be obtained. However, the scaling for regime II (localized) deviates significantly from classic law. The underlying mechanism is that the reaction-induced gas phase forms a layer, acting as a barrier that hinders contact between the acid and rock. Consequently, the error between measurement and prediction continuously amplifies as dissolution proceeds; the predictability is poor. We propose a theoretical model that describes the regime transition, exhibiting excellent agreement with experimental results. This work offers guidance on the usage of scaling law in multiphase flow environments. Fluid-rock dissolution is ubiquitous in natural and engineered systems, including karst formation, geological carbon sequestration, and acid stimulation. Recent developed method for CO2 sequestration relies on mineralization, which transforms CO2 into carbonate minerals through geochemical reactions involving dissolution. The precise modeling of dissolution processes at the continuum-scale is dependent on the estimation of the overall dissolution rate using surface-volume scaling laws. This important scaling law is always established in a single-phase system. Here, through limestone-based microfluidics experiments, we find that the scaling is significantly affected by the dissolution regime in a multiphase flow environment. When the injection rate is lower, and the geometry is more homogeneous, the dissolution regime adheres to classic law. On the other hand, when the flow is stronger and the heterogeneity exhibits, the dissolution scaling significantly diverges. Our discovery indicates that a layer of CO2 gas attaches to the uneven surface, causing a shielding effect on the dissolution and resulting in a notable deviation. Through establishing a theoretical model for the regime transition, this work offers guidance on the usage of scaling law across various dissolution scenarios. The newly developed scaling can enhance dissolution modeling precision in multiphase flow-dissolution systems such as geologic carbon sequestration. We observe two regimes, and the scaling in regime II deviates significantly from classic law, with a poor predictability of dissolution rateWe identify a barrier effect in real rock samples that inhibits the contact of acid and rock for the deviation of scaling in regime IIWe propose a theoretical model for regime transition that offers guidance on the usage of scaling law in multiphase environment