Laboratory Studies of Gas Flow Through a Single Natural Fracture

Abstract

The relationship between the aperture and gas conductivity of a single natural fracture was investigated in the laboratory. Fracture conductivity was evaluated as a function of both the applied fluid pressure gradient and average fracture aperture, the latter ranging from 600 to 200 μm. Fracture apertures were determined independently on the basis of both fracture deformation and fracture volume measurements. Flow generally occurred in the linear and transitional flow regime between linear and fully nonlinear flow. The transition was found to be smooth and well described by an equation of the form: −(dp/dx) = av + bv2, where dp/dx is the pressure gradient and v is the fluid velocity. The linear and nonlinear fracture conductivities were found to be functions of the aperture and surface roughness of the fracture in agreement with existing empirical equations. A new physical model for fracture flow is also formulated based on an analogy to pipe flow.

Numerical simulation of air- and water-flow experiments in a block of variably saturated, fractured tuff from Yucca Mountain, Nevada

“…In other words, in order to approximate the effects of variable saturation, fracture transmissivities in the MAFIC input file were manually adjusted at each of six average matric potentials selected to encompass the range of matric potentials imposed in the experiment. The apertures used to estimate the unsaturated fracture transmissivities in MAFIC were twice as large as those listed in table 7, in accordance with the observation from both experiments (Schrauf and Evans, 1986) and the numerical simulations described earlier that mean physical aperture is roughly twice the equivalent hydraulic or pneumatic aperture calculated from the cubic law. Table 9 lists the transmissivity values for individual fractures at each matric potential considered.…”

“…Their measured curves exhibited hysteretic behavior and relatively distinct air-entry pressures and were welldescribed by functional relations originally developed for porous media. The pneumatic properties of fractures in tuff and their relation to average physical apertures were presented in Schrauf and Evans (1986), who also presented techniques for identifying nonlinear flow behavior during air-injection tests.…”

Assessment of the State-Of-The-Art of Numerical Simulation of Enhanced Geothermal Systems

“…"However, Schrauf and Evans (1986) made the important observation that although the full form of the cubic law may not hold, it is often the case that increments of closure result in changes in ah which are only slightly smaller, at least provided that the closure is not great.…”

The seismo-hydro-mechanical behaviour during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in-situ stimulation experiment

“…24 57 hours a day, year-round) and the increased aversion to nuclear power generation have 58 motivated global efforts to optimize methods for extracting deep geothermal energy for 59 electricity production. However, currently, geothermal power production is limited to distinct 60 geological conditions, where fluid flow rate in geothermal reservoirs carry sufficient heat 61 (Saar, 2011) incremental form of the cubic law might hold such that changes in mechanical aperture give 296 rise to equal changes in hydraulic aperture, at least for normal loading (e.g., Schrauf and 297 Evans, 1986;Evans et al 1992;Chen et al, 2000). For shear-induced dilation, an additional 298 complication arises from channel clogging due to gouge production (e.g.…”