Matrix diffusion is an important mechanism for solute transport in fractured rock. We recently conducted a literature survey on the effective matrix diffusion coefficient, D(m)(e), a key parameter for describing matrix diffusion processes at the field scale. Forty field tracer tests at 15 fractured geologic sites were surveyed and selected for the study, based on data availability and quality. Field-scale D(m)(e) values were calculated, either directly using data reported in the ...

Because the continuum approach is relatively simple and straightforward to implement, it has been commonly used in modeling flow and transport in unsaturated fractured rock. However, the usefulness of this approach can be questioned in terms of its adequacy for representing fingering flow and transport in unsaturated fractured rock. The continuum approach thus needs to be evaluated carefully by comparing simulation results with field observations directly related to unsaturated flow and ...

Ground deformation, commonly observed in storage projects, carries useful information about processes occurring in the injection formation. The Krechba gas field at In Salah (Algeria) is one of the best-known sites for studying ground surface deformation during geological carbon storage. At this first industrial-scale on-shore CO2 demonstration project, satellite-based ground-deformation monitoring data of high quality are available and used to study the large-scale hydrological and ...

This paper presents a hysteretic water retention curve (WRC) and unsaturated hydraulic conductivity model for deformable soils based on the change in pore-size distribution (PSD). The PSD plays a decisive role in the water retention behaviour of soils. Although its evolution during deformation is rather complicated, experimental data showed that the overall shapes and distribution characteristics of the PSD function are not significantly altered. Based on these findings, the PSD function ...

This paper presents simulation results related to coupled thermal–hydraulic–mechanical (THM) processes in engineered barrier systems (EBS) and clay host rock, in one case considering a possible link to geochemistry. This study is part of the US DOE Office of Nuclear Energy’s used fuel disposition campaign, to investigate current modeling capabilities and to identify issues and knowledge gaps associated with coupled THMC processes and EBS–rock interactions associated with repositories ...

The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca ...

Injectivity is critical for injection of CO2 into saline aquifers. Previous model studies indicate that injectivity can be impaired by salt precipitation near the injection well. These results are largely determined by the relationships between permeability and salt precipitation. In this study, we develop a new relationship for permeability change owing to salt precipitation near a CO2 injection well. This relationship differs from previous relationships in that it considers the fact ...

One of the most important design variables for a geological nuclear waste repository is the temperature limit up to which the engineered barrier system (EBS) and the natural geologic environment can be exposed. Up to now, almost all design concepts that involve bentonite-backfilled emplacement tunnels have chosen a maximum allowable temperature of about 100°C. Such a choice is largely based on the consideration that in clay-based materials illitization and the associated mechanical ...

Preferential flow and solute transport are common processes in the unsaturated soil, in which distributions of soil water content and solute concentrations are often characterized as fractal patterns. An active region model (ARM) was recently proposed to describe the preferential flow and transport patterns. In this study, ARM governing equations were derived to model the preferential soil water flow and solute transport processes. To evaluate the ARM equations, dye infiltration ...

Preferential flow in the unsaturated soil is an important and common phenomenon, which is difficult to characterize. The major objective of this study was to analyze preferential flow distributions using visualized soil water flow patterns and the active region model (ARM), which has been developed recently. Thirteen infiltration experiments were conducted in the field, including different soils, various initial and boundary conditions controlling the infiltration processes, and ...

Recent studies have shown that fractional Brownian motion (fBm) and fractional Gaussian noise (fGn) are useful in characterizing subsurface heterogeneities in addition to geophysical time series. Although these studies have led to a fairly good understanding of some aspects of fBm/fGn, a comprehensive introduction to these stochastic, fractal functions is still lacking in the subsurface hydrology literature. In this paper, efforts have been made to define fBm/fGn and present a ...

We have developed a new coal-permeability model for uniaxial strain and constant confining-stress conditions. The model is unique in that it explicitly considers fracture–matrix interaction during coal-deformation processes and is based on a newly proposed internal swelling stress concept. This concept is used to account for the impact of matrix swelling (or shrinkage) on fracture-aperture changes resulting from partial separation of matrix blocks by fractures that do not completely cut ...

To reveal the sources of energy-saving potential of each component and compare the thermodynamic properties of the compressed air energy storage (CAES) system and the supercritical compressed CO2 energy storage (SC-CCES) system, most related works have been done using conventional exergy analysis. However, conventional exergy analysis cannot reveal the thermodynamic interactions among components. Therefore, conventional and advanced exergy analyses are applied to evaluating the CAES and ...

As the effective stress increases, low-permeability rock undergoes fairly small porosity changes, but significant decrease in the permeability. Empirical relationships based on laboratory-measured data, typically exponential or power laws, have been proposed to describe the stress–permeability, stress–porosity, and permeability–porosity relationships. However, these approximations yield poor fitting in low effective stress ranges, or unreasonable prediction for certain effective ...

Summary Tensile strength is a critical parameter for hydraulic fracturing, predicting fracture initiation and propagation in reservoirs, especially in shale reservoirs with complex natural fractures and fissures. The tensile strength of conventional rocks, such as sandstone and limestone, has been well-studied and -documented. There are many studies of the tensile strength of laminated shale, which focus on scale effects, loading direction, and temperature effects; however, the studies ...