Capillary rise in vuggy porous media

• https://doi.org/10.2118/194201-PA

Abstract — A formation-damage experimental study is conducted on synthetic homogeneous and vuggy cores. Glass beads of 1.0 mm are sintered to form a uniform core with a porosity of 42%, and finer-sized glass beads (25 and 100 µm) are used as the infiltrates. Glass beads are used as the matrix and infiltrate to reduce surface forces, and the flow is gravity dominated. Dissolvable inclusions are added during the sintering process to create vugs in the core. The pore-size to vug-size ratio is 1:100. The injected-particle sizes are chosen such that straining is the dominant trapping mechanism during the flow experiment. Infiltrate particles are injected at different flow configurations, and the resultant porosity, permeability, and effluent volume are measured. The results can be summarized as follows: Vugs get up to 32% smaller caused by the flow for the infiltrate, while the maximum change in the porosity is observed at the bottom end of the core, vug shape changes to a smoother and rounded surface, and particles go deeper (8 mm more) into the formation when vugs are present, causing damage deeper inside the formation.

• https://doi.org/10.1016/j.advwatres.2020.103671
• 10.1016/j.advwatres.2020.103671

Abstract — Carbonates are highly heterogeneous formations with large variations in pore size distribution and pore space topology, which results in complex multiphase flow behavior. Here we investigate the spontaneous imbibition behavior of fluids in vuggy carbonates. Glass beads of 1.0 mm diameter, with dissolvable inclusions, are sintered to form multiple configurations of heterogeneous vuggy core with variations in matrix porosity, vug size, vug spatial location, and number of vugs. The core fabrication process is repeatable and allows the impact of vug textural properties to be investigated in a controlled manner. Capillary rise experiments are conducted in these proxy vuggy carbonate core and compared with the homogeneous non-vuggy core as reference. Continuous optical imaging is performed to track the position of the air-water interface in the cores. To understand the change in capillary height in the presence of a vug, a volume-of-fluid two-phase numerical simulation is performed in a parallel set of connected and disconnected tubes. Finally x-ray tomography scans are performed to identify the shape of the air-water interface in a select few cores. The results can be summarized as follows: disconnected vugs result in higher capillary rise compared to non-vuggy porous media. The vugs act as capillary barriers, diverting fluid flow to the adjacent connected channels, which ultimately results in a higher overall capillary rise. The results of this work highlight that radius of spontaneous invasion of aqueous phases, such as fracture fluid and hazardous wastes, are affected by vug porosity but not their distribution.