Pore‐Scale Visualization and Quantification of Dissolution in Microfluidic Rough Channels

• Published in: Water resources research 2022-11, Vol.58 (11), p.n/a
• Main Authors: Zhou, Chen‐Xing, Hu, Ran, Li, Hong‐Wei, Yang, Zhibing, Chen, Yi‐Feng
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbon sequestration; Cavity expansion; Channels; Diffusion; Diffusion rate; Dissolution; dissolution experiment; dissolution rate; Dissolving; Dynamics; Evolution; Flow profiles; Flow velocity; Fractures; Geological faults; In situ leaching; Karst; Local flow; Mass transfer; mass transfer rate; Microfluidics; micro‐PIV; Petroleum; Smoothing; smoothing effect; soluble microfluidic; Surface roughness; Surface roughness effects; Velocity; Velocity distribution; Velocity profiles; Visualization
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2022WR032255

The dissolution dynamics of rough channels is a fundamental issue involved in widening fracture channels (cavity evolution), solution mining, and upscaling of dissolution rate. Previous studies have focused on the dissolution patterns at the sample scale, but the study of rough surface evolution at the pore scale is lacking. Here, we fabricate a soluble microfluidic chip with rough channels to investigate pore‐scale dissolution dynamics. Through direct, real‐time imaging of dissolution processes together with micro‐PIV measurements, we observe two distinct dissolution patterns and the roughness smoothing effect. The smoothing effect is characterized by the disappearance of small‐scale peaks and the rapid decline of the surface roughness factor. We demonstrate that this smoothing effect is attributed to the heterogeneous dissolution rates resulting from surface roughness. Through micro‐PIV measurements, we quantify that the roughness smoothing significantly affects the local mass transfer rate by modifying local flow velocity at the scale of 200 μm and by shrinking the diffusion zone (including eddy) at the scale of 2 mm, accelerating the mass transfer rate between diffusion and main flow zones. Due to the smoothing effect, the enhanced local mass transfer rate eventually intensifies the overall dissolution rate. Finally, we provide a theoretical prediction for the transition of two dissolution patterns, which agrees well with experimental observation. Our work develops a useful tool for studying the pore‐scale dissolution behavior in 2D rough channels and improves our understanding of how the pore‐scale dissolution behavior affects the overall dissolution rate and dissolution patterns. Plain Language Summary Understanding the geometry evolution of 2D rough channels or rough fractures subjected to reactive flow conditions is important in many geophysical processes and engineering practices, including the cavity expansion in a karst area, CO2 leakage through rock fractures or faults in geologic carbon sequestration and the acidizing stimulation of petroleum reservoirs. Much of the research has focused on dissolution patterns at the sample scale. At the pore scale, however, how the reactive flowing fluid reshapes the rough walls of channels or fractures is not well understood. To understand the pore‐scale dissolution behavior and its effect on dissolution rate, we perform flow‐through dissolution experiments in soluble rough channels. Through flow‐visualizati