Computed tomography imaging of air sparging in porous media

Abstract

This paper describes the use of an X ray computerized tomography scanner for noninvasive, three‐dimensional, high‐resolution imaging of air distribution patterns during air sparging in water‐saturated sandpacks. Experiments were performed in Plexiglas cylindrical cells using well‐defined Ottawa sands. The reconstructed images provide detailed porosity and air saturation distributions previously unavailable. Two classes of behavior were observed. In high‐permeability (106 darcy) uniform sandpacks a relatively few, discrete, and tortuous air pathways were formed. Steady state was rapidly attained, and the intrachannel air saturations were low (0.10). In contrast, low‐permeability (3 darcy) sandpacks increased the breadth of air contact, delayed attainment of steady state, and displayed high air saturations (0.50). The concept of a hydrodynamic stagnation saturation and standard one‐dimensional fractional flow theory proved useful in explaining the experiments. Numerical simulation confirms the explanations, even when capillary pressure and compressibility effects are included.