Ostwald ripening: Bubble distribution evolution in porous media

Ostwald ripening phenomenon is important in analysing geological gas storage projects where coarsening can lead to increased mobility of isolated gas bubbles. It is a spontaneous diffusive mass transfer from bubbles at higher pressure to those at lower pressures. Gas storage is typically carried out in deep saline aquifers or depleted hydrocarbon fields, presenting both two-phase and three-phase environments for ripening. We present a chemical potential difference based methodology compatible with parallel computations for simulating the Ostwald ripening of gas ganglia surrounded by liquids in arbitrary pore geometries. The method is coupled to a conservative level set model for capillary-controlled displacement. The model can conserve more than one phase to assess the impact of isolated oil and water phases in the system and handles real gasses. We simulate different fluid distributions and pore geometries in two-phase and three-phase ripening scenarios to study the impact of isolated residual phases, gas type, three-phase distributions, and wetting states. The results show that gas solubility and compressibility factor, local capillary pressure, and pore geometry affect the mass transfer rate. In a three-phase scenario, the equilibrium distribution of residual gas bubbles depends strongly on the initial three-phase fluid configuration and its properties (e.g., interfacial tension, wetting state, and interfacial area). The presence of oil ganglia speeds up the local coarsening process, while the presence of an isolated intermediate fluid phase can stabilise smaller bubbles. During fluid redistribution, we also identify cases with three-phase double displacements.