Wettability-dependent DNAPL migration in a rough-walled fracture

The migration of dense non-aqueous phase liquids (DNAPLs) in fractured rock is poorly understood in the context of surface wettability. Prior research has shown that DNAPL movement is influenced by fracture geometry and fluid flow conditions. However, no prior work had resolved how surface wettability affects DNAPL migration in rough-walled fractures. This gap motivated a closer examination of how contact angle and fracture surface properties interact with DNAPL flow. Existing studies typically focus on smooth fractures or do not isolate wettability effects. This study introduces a controlled experimental setup to isolate wettability's role. It was already known that DNAPLs tend to pool in fractures, but the mechanisms behind their migration remained unclear. This paper addresses the uncertainty by testing DNAPL movement under different wettability conditions. The results provide new insights into how DNAPLs behave in complex fracture geometries.

The aim of this study was to determine how DNAPL migration is influenced by the wettability of fracture surfaces. The researchers focused on how DNAPLs move through rough-walled fractures under varying wettability conditions. The motivation came from the need to better understand subsurface fluid dynamics in fractured rock systems. DNAPLs are known to pose environmental risks, so understanding their migration is crucial for remediation efforts. The study sought to clarify whether surface wettability could be used to predict or control DNAPL movement. It also aimed to test whether capillary and gravity pressures dominate under different wettability scenarios. The researchers proposed that surface properties could influence DNAPL migration patterns. This work may help improve models of contaminant transport in fractured media.

The study used a laboratory setup with a transparent, rough-walled fracture to simulate natural rock fractures. Three different wettability conditions were tested: hydrophilic, intermediate-wet, and hydrophobic surfaces. DNAPL migration was observed under linear and nonlinear groundwater flow regimes (Re=1 and Re=60). The researchers used high-speed imaging to track DNAPL movement through the fracture. They measured how DNAPL distributed across apertures of different sizes. Contact angles were measured to classify the wettability of each surface. Gravity and capillary pressures were calculated to assess their influence on migration. The study compared DNAPL migration paths and velocities under each condition.

DNAPL migration was fastest on intermediate-wet surfaces with a contact angle of about 90 degrees. On hydrophilic surfaces, DNAPL moved as disconnected blobs through larger apertures when Re=1. Hydrophobic surfaces retained DNAPL, forcing it to migrate through smaller apertures due to capillary barriers. At Re=60, DNAPL generally moved downward due to inertial pressure, but migration speed still varied by surface wettability. The fastest migration occurred on hydrophilic surfaces, while the slowest was on hydrophobic ones. The study found that capillary pressure dominated in linear flow, while inertial pressure was more significant in nonlinear flow. DNAPL migration was most unpredictable on hydrophobic surfaces. These findings suggest that surface wettability strongly influences DNAPL movement patterns.

The authors suggest that DNAPL migration is strongly influenced by surface wettability in rough-walled fractures. They propose that intermediate-wet surfaces may be most favorable for DNAPL movement due to the dominance of gravity pressure. Hydrophilic surfaces allow for faster DNAPL migration in linear flow regimes. Hydrophobic surfaces tend to retain DNAPL, forcing it to move through smaller apertures. The study implies that capillary barriers are more significant in linear flow conditions. Inertial pressure becomes more important in nonlinear flow regimes. The researchers suggest that these findings may have implications for DNAPL and oil recovery in fractured media. They propose that surface wettability could be used to predict or control DNAPL migration in subsurface systems.