The dimensional character of permeability. Dimensionless groups that govern Darcy’s flow in anisotropic porous media.

The dimensional character of permeability in anisotropic porous media, that is,its dimension or dimensional equation, is an information that allows setting thedimensionless groups that govern the solution of the flow equation in terms ofhydraulic potential patterns. However, employing the dimensional basis {L, M,T} (length, mass, time), the dimensionless groups containing the anisotropic per-meability do not behave as independent monomials that rule the solutions. Inthis work, the contributions appearing in the literature on the dimensional char-acter of permeability are discussed and a new approach based on discriminatedand general dimensional analysis is presented. This approach leads to the emer-gence of a new and accurate dimensionless group,kxkyl∗2yl∗2x, a ratio of permeabilitiescorrected by the squared value of an aspect factor, beingl∗xandl∗ytwo arbitrarylengths of the domain in the directions that are indicated in their subscripts. Spe-cific values of this lengths, which we name ‘hidden characteristic lengths’, arealso discussed in this article. To check the validity of this dimensionless group,numericalsimulationsoftwoillustrative2-Dseepagescenarioshavebeensolved.The authors would like to thank SéNeCa Foundation for the support given to this research and for the scholarships awarded to Martínez-Moreno E. to carry out her doctoral thesis

Estudio numérico de las cuñas salinas y de recirculación en el problema de Henry mediante los grupos adimensionales discriminados

[ESP] El problema patrón de Henry, que describe los fenómenos de flujo y transporte que emergen en escenarios de intrusión salina en acuíferos costeros, está regido por un sistema acoplado de ecuaciones en derivadas parciales. La caracterización del mismo, a partir de la adimensionalización discriminada de sus ecuaciones, conduce a dos grupos adimensionales que definen los patrones estacionarios de flujo y concentración, grupos que se diferencian de los establecidos por Henry y adoptados por la comunidad científica en las últimas décadas. Mediante el método de redes se simula este problema para un rango suficiente de valores de estos grupos, comprobando que las longitudes de la cuña de intrusión y de recirculación se diferencian a medida que nos alejamos de los valores de Henry, llegando a desaparecer la recirculación de agua salada junto al lado del mar. Para evitar la influencia de la longitud del acuífero en la solución se ha aumentado ésta suficientemente en cada caso. [ENG] The Henry benchmark problem, that describes the fluid flow and solute transport phenomena involved in salt intrusion scenarios in coastal aquifers, is ruled by a set of coupled partial differential equations. Its mathematical characterization, from the discriminated nondimensionalization of the equation, leads to the two dimensionless groups that define the solution patterns of stream function and concentration. These differ from those of henry already accepted by scientific community along the last decades. By the network method, this problem is simulated for a large number of pairs of values of the groups, demonstrating that the lengths of the concentration and recirculation wedges, measured at the bottom of the aquifer, differ as values moves away from Henry arriving be disappear. The length of the aquifer is enlarged to avoid its influence in the steady state patterns.Centro Universitario de la Defensa. Escuela de Turismo de Cartagena. Escuela Técnica Superior de Ingeniería Industrial UPCT. Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT). Escuela de Ingeniería de Caminos y Minas (EICM). Escuela de Arquitectura e Ingeniería de Edificación (ARQ&IDE). Parque Tecnológico de Fuente Álamo. Navantia. Campus Mare Nostrum. Estación Experimental Agroalimentaria Tomás Ferr

POTENTIAL EFFECTS OF GEOLOGIC STORAGE OF CO2 ON SURFACE WATER AND SHALLOW GROUNDWATER

ABSTRACT Storage of supercritical phase CO2 in deep saline aquifers is being considered to reduce greenhouse gases in the atmosphere, and this process is expected to increase the pressure in these deep aquifers. One potential consequence of pressurization is an increase in the upward flux of saline water. Saline groundwater occurs naturally at shallow depths in many sedimentary basins, so an upward flux of solutes could degrade the quality of aquifers, and threaten aquatic ecosystems where groundwater discharge is important. The objective of this research is to evaluate the impacts associated with increasing the upward flux of saline water as a result of CO2 storage, or other effects. The approach was to develop and evaluate simulations of salt concentration in a fresh water aquifer overlying saline groundwater that is subjected to changes in flux. The first task was to verify the solution of benchmark problems of density-dependent flow using the computational codes COMSOL Multiphysics. The COMSOL code was then used to analyze idealized 2D and 3D geometries representing the essential details of a shallow, fresh water aquifer underlain by a saline ground water in a sedimentary basin. The analysis was conducted in two stages, one that simulated the development of a fresh water aquifer by flushing out salt water, and another that simulated the effect of a pulse-like increase in the upward flux from the basin. The effects of saline encroachment were evaluated using a sensitivity analysis of key parameters, and the results were formulated in both dimensioned and dimensionless form. The results indicate that the depth of the fresh/salt interface is a function of the recharge rate, duration of fresh water flushing/basin flux rate, density of the saline water, as well as the formation anisotropy. The fresh/salt interface was found to be more uniform and shallower as the density of the salt water increased. Increased upward flux of saline water raised the fresh/salt interface, and it increased the salinity of water discharging to streams. However, the magnitudes of these effects appeared to be small. For example, the mass loading of chloride to streams only exceeded the TMDL for chloride at a reference location under extreme conditions. Nevertheless, the increases in chloride concentration in the fresh water system are long-lived, so this effect should be considered when designing a CO2 storage project. The significant contributions of this study include 1) identification of important controls on the encroachment of saline ground water on overlying fresh water resources; 2) evaluation of the expected impacts posed by increased flux from saline aquifers caused by CO2 storage

Controls on groundwater and surface water salinity in coastal Bangladesh

Salinity in surface water and groundwater is a pervasive issue along coastal Bangladesh, a low-lying megadelta where around 35 million people live. A large amount of this land has been reclaimed using a network of low-lying polders. The area is particularly susceptible to flooding from tropical cyclones. Cyclone induced storm surges coupled with the low-lying reclaimed land can breach polder embankments and cause extensive flooding, resulting in excess salinity in soil and surface water. Salinity in drinking water is known to cause adverse effects on human health. It is, therefore, important to identify the controls surface water and groundwater salinity in these coastal areas. A fully coupled surface-subsurface model of a coastal polder by using HydroGeo- Sphere is developed to investigate the impact of storm surge events on groundwater salinity. The hydrological parameters were calibrated from the fieldwork at a field site in the Dacope Upazila, in the southwest coastal region of Bangladesh. The results suggest that sudden salt fluxes in the pond are likely to build up salinity in the underlying sediment. A set of scenarios were considered: a cyclone induced storm surge during both the monsoon and dry seasons, and both with and without remediation. The results show that surge events caused a rise in salinity in drinking water and near-surface groundwater. However, rapid remediation after a surge event could help mitigate the severity of the impact on drinking water. This provides suggestions for water resources management planning. The 2D cross-section model was extended to the 3D model to improve the understanding of the salinity process. Climate change scenarios were then used to evaluate the effects of episodic cyclone surges on shallow groundwater salinity. This study suggests that more frequent cyclones would worsen not only salinity in near-surface groundwater but lateral saltwater intrusion at the shallow or deep aquifers.Open Acces

Numerical investigations of heat and mass transport in fractured porous rock masses

Fluid flow processes in the subsurface are accompanied by heat and mass transport with several important feedbacks including reactive flow, and precipitation/dissolution processes. Heat and mass transport through fractured rock masses occurs in many natural systems such as the plumbing of volcanic systems, mesothermal ore deposits, and post-seismic fluid flow. Anthropogenically-driven systems, such as fluid-injection in Enhanced Geothermal Systems (EGS), and the injection of waste-water from hydrocarbon extraction also involve heat and mass transport through porous or fractured rocks. Understanding in detail how mass and heat transfer interact in natural or in industrial applications requires numerical models in combination with field and laboratory experiments to determine the dominating factors. This thesis examines the impact of heat and mass transport on high pressure fluid propagation in the subsurface, as well as different numerical approaches of transient heat flow in fractured porous media and the heat exchange between flowing fluid and host rock. Many fluid-triggered seismic events show a tendency for upward migration of the seismic cloud, generally assumed to reflect a fluid-pressure dependent permeability. In a numerical investigation that combines pressure-dependent permeability with thermal and salinity effects, it is found that over short timescales pressure-dependent permeability does indeed have the strongest influence on asymmetric diffusion. However, it is also demonstrated that over longer timescales, for example the lifetime of a geothermal reservoir, temperature and salinity effects play an increasingly important role. Assessing the thermal field of a geothermal resource or in a CO2 sequestration project is essential for proper design and management. Typically, numerical simulations assume that the fluid and solid phases are in thermal equilibrium, an assumption that has to date not been investigated in detail. This assumption is examined in this work by simulating fluid and heat flow in a simple geometry to analyse the influence of site specific parameters on the simulation result. It is shown that the equilibrium model is not sensitive to porosity contrasts, while the non-equilibrium model shows a sensitivity to porosity contrasts, with simulation results diverging more strongly in less permeable zones. In a simulation of a hypothetical geothermal system, the equilibrium model shows higher production temperatures with a divergence of up to 7% between the approaches, which could impact the economic feasibility of a project. Finally, a new approach is introduced to determine the heat transfer coefficient h between rock walls and flowing fluid using the non-equilibrium model. Based on a numerical experimental setup with simple geometry and steady state scenario, a dynamic heat transfer coefficient is derived that depends on fracture aperture and flow velocity. This model is based on well-defined physical parameters, it is adaptable to complex geometries, and intrinsically adjusts to spatial heterogeneities and temporal changes in flow and temperature field. A possible extension of this dynamic approach is demonstrated in numerical simulations the reservoir scale