Onset dynamics of air-water menisci on rock fracture surfaces

B. B. Horodecky, E. Perfect, H. Z. Bilheux, J. W. Brabazon, C. H. Gates

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Information on menisci dynamics and equilibrium contact angles, θe, is needed for modeling multiphase flow of fluids in geologic formations. The wettability of fracture faces is relevant to applications such as waterflooding in enhanced oil recovery and evaluation of caprock integrity for geologic carbon sequestration. We investigated the vertical capillary rise of air-water menisci on exposed fracture faces for a sandstone, a shale, and three granites. The experimental design approximated that employed in the Wilhelmy plate method. Replicate fracture faces were prepared by fracturing cylindrical rock cores using the Brazilian method and splitting the fractured cores apart along their fracture planes. Meniscus onset was imaged from a cross-sectional perspective using dynamic neutron radiography, and quantified with change point analysis. An existing model for meniscus onset fitted the experimental data very well (median R2 = 0.96). Capillary rise was typified by [Formula Presented] scaling (where t is time), followed by a constant equilibrium height, ze. The average time taken for the menisci to reach ze was 0.39 s, with no differences between rock types. The menisci achieved a greater vertical extent on the fracture faces of the sedimentary rocks as compared to those of the granites. Apparent θe values were calculated from the best fit estimates of ze using the Wilhelmy plate equation for a smooth and planar vertical surface. Despite the fractal roughness of some of the fracture faces, there was a significant linear relationship (R2 = 0.80) between the apparent θe values and intrinsic θe values measured on polished surfaces of the same rocks using the sessile drop method. The regression equation indicated the apparent θe values were consistently greater than the intrinsic values. This overestimation may be due to averaging of pixels at the air-water-solid interface, a required step in the image analysis. Further exploration of the range of applicability and measurement accuracy of this proposed new technique would be valuable.

Original languageEnglish
Article number103754
JournalAdvances in Water Resources
Volume146
DOIs
StatePublished - Dec 2020

Funding

This research was sponsored by the Army Research Laboratory and was accomplished under Grant Number W911NF-16-1-0043. Portions of this research utilized resources at the High Flux Isotope Reactor and Center for Nanophase Materials Sciences, which are DOE Office of Science User Facilities operated by Oak Ridge National Laboratory. E. Perfect acknowledges support from the Tom Cronin and Helen Sestak Faculty Achievement award.

Keywords

  • Contact angle
  • Inertial capillarity
  • Meniscus shape
  • Neutron radiography
  • Surface roughness

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