Experimental studies of water seepage and intermittent flow in unsaturated, rough‐walled fractures

Abstract

Abstract. Flow visualization experiments were conducted on a transparent replica of a natural, rough-walled rock fracture from the Stripa Mine, Sweden, for inlet conditions of constant pressure and flow rate over a range of angles of inclination. The experiments demonstrated that infiltrating water proceeds through unsaturated rock fractures along nonuniform, localized preferential flow paths. Even though constant inlet conditions were maintained, pervasive unsteady or intermittent flow was also observed in these experiments, where portions of the flow channel underwent cycles of snapping and reforming. Experiments conducted on parallel plates with a sequence of apertures progressing from small to large to small reproduced intermittent flow. Measurements of the frequency of intermittent flow events and the volume of water metered between events were obtained from the fracture replica and parallel plate experiments and related to the Bond and capillary numbers to generalize the results. The frequency data from the fracture replica experiments did not follow the same trend as the data from the parallel plate experiments for similar Bond and capillary numbers, but the volume of water metered data was consistent in these experiments. IntroductionFractures in the unsaturated zone play an important role in water infiltration and contaminant transport. Field studies have provided considerable evidence that water proceeds along fast flow paths through partially saturated fractures. Bomb-pulse Chlorine 36 at Yucca Mountain, Nevada, was found at elevated concentrations several hundred meters deep, indicating that water had migrated from the land surface to these depths in a time period of only several decades [Liu et al., 1995]. Seeps collected in tunnels at Rainier Mesa, Nevada, were chemically distinct from matrix water, and their isotopic ratios indicated recent meteoric origin [Wang et al., 1993]. Recharge water was observed to flow quickly through a thick unsaturated fractured chalk zone in the Negev Desert in Israel [Nativ et al., 1995]. These observations were explained by water migrating rapidly along localized preferential flow paths through unsaturated rock fractures. Preferential flow channels reduce rock matrix-fracture interaction compared to models that predict spatially uniform flow, thereby accelerating groundwater travel in unsaturated fractured porous media [Glass et al., 1995]. Understanding the mechanisms controlling fast flow is important for developing conceptual models describing seepage of liquids through unsaturated, fractured porous media.Liquids in unsaturated porous media migrate under the combined action of gravity, pressure, capillary, and viscous forces. The relative magnitude of these forces can be quantified using the Bond and capillary numbers. The ratio between where A 9 is the density difference between the infiltrating liquid and the air, !7 is the gravitational acceleration constant, /3 is the angle of inclination of the fracture measured from the horizontal, b is the aperture, cr is ...

Unsaturated flow and transport through a fault embedded in fractured welded tuff

“…[35] While both laboratory and field observations [e.g., Trautz and Wang, 2002;Dahan et al, 1998;Su et al, 1999], including those in this study, consistently show the existence of dynamic flow behavior in unsaturated fractured rock at different scales, the temporal and spatial scales of the problem under consideration largely determine the practical importance of this dynamic behavior. For example, if our concern is the flow process for a given flow path, the dynamic behavior can be a dominant factor, one that needs to be considered (e.g., tray 6 in Figure 6).…”

“…A typical example is the flow path(s) associated with tray 6, within which there was a large degree of temporal variability in seepage rates. Trautz and Wang [2002] and Dahan et al [1998] have also reported similar dynamic flow behavior in unsaturated fractures, which may result from a combination of mechanisms such as gravity-driven instabilities [Nicholl et al, 1992[Nicholl et al, , 1993a[Nicholl et al, , 1993b[Nicholl et al, , 1994, the development of capillary islands [Su et al, 1999], or switches along fracture intersections [Glass et al, 2002]. Additional mechanisms include alterations to the fault surface brought about by the shrinking/swelling of infill material within the fault [Salve and Oldenburg, 2001] and other alterations to fracture surfaces [e.g., Weisbrod et al, 1998Weisbrod et al, , 1999Weisbrod et al, , 2000.…”

TH{_}PULSE: Program for Calculating Infiltration of Episodic Liquid Fingers in Superheated Rock Fractures - Theory, User's Manual and Sample Applications

“…In recent years, a number of laboratory, field, and theoretical studies have been performed to analyze localized preferential flow paths in unsaturated sub-boiling fractures [e.g., Glass, 1993;Nicholl et al, 1994;Glass and Nicholl, 1996;Pruess, 1998;Su et al, 1999]. It was consistently observed that liquid flow forms in narrow fingers under mainly gravitational forces, and that fingering flow often occurred in intermittent rivulets, induced by gravitational instability.…”

“…This method has been shown to give good accuracy for heat exchange between reservoir fluids and confining beds [e.g., Pruess et al, 1999]. In TH_PULSE, the method was included mainly to allow direct comparison with TOUGH2 simulation runs, where the same heat exchange approach can be utilized.…”

Experimental investigation of heat transfer in a falling down rivulet of liquid FC-72 on the vertical heated foil

“…The results of such studies were used to plot the maps of varieties of rivulet flows of different liquids (water, water solution of ethyl alcohol, water solution of glycerine) over the inclined plate. As the liquid flow rate increased, the drop flow, straight flow, meandering flow, which converted into the film flow [2][3][4], were observed.…”