Capillary rise in vuggy media

TL;DR

This study investigates how vugs in carbonate rocks influence capillary rise, revealing that disconnected vugs increase capillary height by acting as barriers and diverting fluid flow, with implications for fluid invasion in heterogeneous formations.

Contribution

The paper introduces a controlled experimental setup to analyze the impact of vug textural properties on capillary rise in carbonate analogs, combining physical experiments with numerical simulations.

Findings

Disconnected vugs increase capillary rise compared to homogeneous media.

Vug porosity affects invasion radius, but distribution does not.

Vugs act as capillary barriers diverting fluid flow.

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.