To investigate two-phase fluid flow processes influenced by phase interference, pressure drop, fracture roughness and environmental stress, a nitrogen-water two-phase flow experiment was carried out on highly rough granite fractures in an experimental triaxial cell. Pressure was used to control the two-phase fluid in the fracture. The results show that each fluid phase has a separate flow channel, even through rock fractures of large roughness. Correlation of the superficial velocities of the two-phase fluids identifies the annular flow at a high pressure drop due to the high kinetic energy of the gas phase; however, annular flow transitioned to complex flow with increasing fracture roughness and confining pressure. The relative permeability of water is greater than that of gas. The sum of the relative permeabilities of the two phases is less than unity due to phase interference. With increasing pressure head, confining pressure, and fracture roughness, the relative permeability of water shows a general decreasing trend and the sum of relative permeability continuously reduced, demonstrating that the localized flow paths of the different phases changed and the phase interference increased. The experimental relative permeability of gas is greater here than that determined by the nonlinear viscous coupling model and Corey model, but less than the straight-line relative permeability model (X-model). Among them, the viscous coupling model provides the closest approximation, indicating that the physical process of two-phase flow through highly rough and tight rock fractures is more like that through a pipe, rather than through porous media and parallel-plate channels.

In many regions of the world, crystalline bedrock aquifers are the only choice for groundwater supply. This is the case in northern Wisconsin, located in the upper Midwest of the continental United States. Here, groundwater flow to wells occurs only through fractures in the granitic basement. Although hydrofracturing of these wells is common and generally increases well yield, the precise mechanism for the increased yields remained unknown. Stressed and ambient flow logs were obtained in two 305-m-deep granitic boreholes in northern Wisconsin prior to hydrofracturing. From those logs, it was determined that nearly all of the groundwater flow to the boreholes occurred in less than 10 fractures in the upper 80 m, with no measureable contribution below that depth. Following hydrofracturing of the boreholes, stressed and ambient flow logs were again obtained. The transmissivity of the two boreholes increased by factors of 8.6 and 63 times. It was found that (1) the fractures that had contributed flow to the boreholes increased in transmissivity, (2) although the applied pressures were large enough in some instances to create new fractures, those new fractures did not increase the borehole transmissivities significantly, and (3) fractures without measureable flow before hydrofracturing remained without measureable flow. Hydrofracturing increases yield in granitic boreholes; however, that increase seems to only occur in fractures where flow was pre-existing and in the upper 80 m of the boreholes. These observations suggest that efforts to enhance yield in granitic aquifers should be focused on the upper part of the borehole.

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.