Abstract
Fractures in low-porosity rocks can provide conduits for fluid flow. Numerous researchers have investigated fluid flow through fractures under saturated conditions. However, relatively little information exists on spontaneous imbibition in fractures, whereby a wetting fluid displaces a non-wetting fluid by capillarity. We investigated spontaneous imbibition of water displacing air in a suite of fractured low-porosity sedimentary and igneous rock cores (5.08-cm length by 2.54-cm diameter). Mode I fractures were induced in the cores by compression between opposing parallel flat plates. The following physical properties were measured: bulk density, r b ; solid-phase density, r s ; porosity, f; contact angle, q e ; fracture aperture width, x geo; and fracture surface roughness, W r . The wetting front in each fracture was imaged using dynamic neutron radiography. Early-time uptake exhibited a square root of time dependency, and was quantified by linear regression, with the slope equal to the fracture sorptivity, S f . Estimates of S f ranged from 10.1 to 40.5 mm s −0.5 , with a median value of 25.0 mm s −0.5 . There was a statistically significant effect of rock type on S f , with igneous rocks generally having lower mean values than sedimentary rocks. Differences in r b , r s , f, and q e between the rock types did not contribute significantly to the variation in S f . However, x geo and W r were significantly correlated with S f . These correlations indicated that S f increases with increasing x geo , as predicted by early-time capillary theory, and decreases with increasing W r , analogous to the decrease in fracture permeability with increasing surface roughness observed under saturated flow conditions.
| Original language | English |
|---|---|
| Article number | 180156 |
| Journal | Vadose Zone Journal |
| Volume | 18 |
| Issue number | 1 |
| DOIs | |
| State | Published - 2019 |
Funding
This research was sponsored by the Army Research Laboratory and was accomplished under Grant no. W911NF-16-1-0043. Portions of this research used resources at the High Flux Isotope Reactor, which is a USDOE Office of Science User Facility operated by Oak Ridge National Laboratory. E. Perfect acknowledges support from the Tom Cronin and Helen Sestak Faculty Achievement award. The solid-phase density, dry bulk density, and porosity data were collected by A.D. Vial.