Influence of Pressure Change During Hydraulic Tests on Fracture Aperture

Abstract

In a series of field experiments, we evaluate the influence of a small water pressure change on fracture aperture during a hydraulic test. An experimental borehole is instrumented at the Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The target fracture for testing was found from the analyses of borehole logging and hydraulic tests. A double packer system was developed and installed in the test borehole to directly observe the aperture change due to water pressure change. Using this packer system, both aperture and flow rate are directly observed under various water pressures. Results indicate a slight change in fracture hydraulic head leads to an observable change in aperture. This suggests that aperture change should be considered when analyzing hydraulic test data from a sparsely fractured rock aquifer.

Nonlinear groundwater flow during a slug test in fractured rock

“…Details on the site characteristics of KURT are described by Ji et al (2013). The host rock is a Mesozoic two-mica granite.…”

“…The major pathway for groundwater flow in a crystalline rock is fractures set in a low permeable rock matrix, and the variation of fracture spacing and interconnectivity of the fracture network make crystalline rock very heterogeneous. Moreover, several reported phenomena such as the nonlinear groundwater flow in a fracture (Zimmerman and Bodvarsson, 1996), the directional anisotropy of groundwater flow in a fracture (Boutt et al, 2006) and the aperture change during a hydraulic test (Ji et al, 2013) can make the characterization more uncertain.…”

Hydraulic properties and energy dissipation of deep hard rock under H-M coupling and cycling loads

“…Different stress conditions may cause the fracture opening/closing or shear expansion, which affected the formation of flow paths, the seepage characteristics of rocks would be changed [4]. So the mechanical properties of rocks under hydro mechanical coupled loads had significantly difference [5][6][7]. Many laboratory tests have been conducted to study the permeability evolution of rock samples including limestone, sandstone, and granite under triaxialcompression [8][9][10][11].…”

Effect of Pore Fluid Pressure on the Normal Deformation of a Matched Granite Joint

“…The term "joint" is defined as a crack or fracture in rock when there has been little or no transverse displacement [5]. The aperture of joints or fractures depends on the normal stress and on the pore fluid pressure in some engineering [6][7][8][9][10], such as oil or gas exploitation, enhanced geothermal system, and CO 2 geological storage, underground disposal of nuclear waste, and so on. The normal deformation behaviors of joints play an important role between hydraulic and mechanical coupling processes, because the variation of pore fluid pressure or normal stress will change the aperture, and then the aperture of fracture dominates the hydraulic properties [11,12].…”

“…However, most models tend only to quantify the variation of aperture as a function of normal stress, without considering the influence of pore fluid pressure. Despite the importance of pore fluid pressure, even fewer models considered the influence of pore fluid pressure on the normal deformation of a joint [6,8,10,26]. Some hydro-mechanical coupling models (H-M models) were based on the Terzaghi's effective stress [9,[27][28][29][30] or the Biot's pore elasticity theory [8], and assuming that the normal deformation path of a joint during pore fluid injection is overlapping with the normal stress loading processes.…”