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Multi-Phase Flow Behavior in Low-Permeability Argillaceous Rock (LBNL Contact: Hui-Hai Liu (see contact information below))
Observations of flow processes in low-permeability argillaceous have shown that the traditional Darcy relationship between flow and the piezometric energy gradient is not appropriate. Many of the reports of such behavior are for saturated flow conditions. Although nuclear waste disposal in argillaceous rock is generally being investigated for saturated groundwater systems, the act of constructing the repository leads to desaturation of the rock in the vicinity of the excavations. As a result, for some period of time, a portion of the natural repository system will be unsaturated. This naturally leads to the question of the behavior of unsaturated flow in low-permeability argillaceous rock. Current investigations are looking into the effects of non-Newtonian flow processes and how this may affect unsaturated flow in low-permeability argillaceous rock. Constitutive relationships between water flux and hydraulic gradient and among capillary pressure, water saturation, and hydraulic conductivity have been proposed based on the hypothesis that pore water in clay becomes non-Newtonian as a result of water-clay interaction. These are being evaluated through comparisons with laboratory experimental observations.
Comparisons between calculated (solid curves) and measured (data points) water flux as a function of hydraulic gradient for different capillary pressures. The calculation is based on Equation (2-33). Data from Cui et al. (2008)
Natural analogues (LBNL Contact: Jim Houseworth (see contact information below))
Natural evolution of geologic systems is difficult to observe and predict because of the large spatial domains in which these systems operate, the long (geologic) time scales involved, and complex array of processes involved. One avenue to increase understanding is through observations and modeling of suitable analogues. Argillaceous formations often act as caprocks for petroleum reservoirs. The function of retaining trapped petroleum fluids provides a convenient indicator of formation integrity. Further, because of the economic interest in petroleum systems, many formations have been investigated worldwide. This provides a large information base concerning the evolution of argillaceous formations over a wide variety of geologic environments.
The findings from petroleum analogues highlight a number of natural processes that can affect the low-permeability characteristics of clay/shale formations. These processes include burial, sediment compaction, and dewatering; tectonic deformation, uplift, erosion, and glaciations; osmotic effects and mineral diagenesis; hydrogeologic processes and buoyant geofluids; magmatic intrusions and hydrothermal systems; siliciclastic and salt intrusions; and cavity formation. These processes all lead to mechanical failure of the rock; caprock failure is ultimately caused by changes in fluid pressure and/or rock stress that lead to the generation or reactivation of fractures or faults. Some of these have been directly identified as causing the loss of caprock integrity for petroleum reservoirs. An evaluation of the potential impacts of such processes on nuclear waste disposal in argillaceous rock should consider the impact that may be caused by the presence of preferential flow pathways that are implied by the petroleum analogue information.
Mohr diagrams showing modes of rock failure
Characteristics and Distribution of Argillaceous Formations in the United States (LBNL Contact: Patrick Dobson (see contact information below))
This task is to identify major shale and mudstone-bearing formations in the onshore sedimentary basins in the United States. Extensive evaluations of these basins have been conducted by the oil and gas and energy industries to identify petroleum resources as well as potential sites for geologic sequestration of carbon dioxide. This information is being gathered and synthesized to provide a database of the physical properties of shales and clay-rich rocks as well as the extent, thickness and depth of shale deposits for the purpose of high-level radioactive waste disposal.
|Hui-Hai Liu||Hydrogeology Dept Head
|Jim Houseworth||Staff Scientist||Hydrogeology Department||510-486-6459||510-486-5686||JEHouseworth@lbl.gov|
|Patrick Dobson||Staff Scientist