1,721,142 research outputs found
A novel One Domain Approach for free fluid-porous medium transport simulation. Preliminary results
Full text linkWe present a new numerical solver for free-fluid flowing over and inside a porous medium. It is based over a macroscopic approach and one fictitious medium is assumed inside the domain, according to the One Domain Approach. Preliminary results are shown and compared with the ones provided by the well-known DuMux solver which applies a two Domain Approach
Fronts in two-phase porous media flow problems:The effects of hysteresis and dynamic capillarity
No full textIn this work, we study the behavior of saturation fronts for two-phase flow through a long homogeneous porous column . In particular, the model includes hysteresis and dynamic effects in the capillary pressure and hysteresis in the permeabilities. The analysis uses traveling wave approximation. Entropy solutions are derived for Riemann problems that are arising in this context. These solutions belong to a much broader class compared to the standard Oleinik solutions, where hysteresis and dynamic effects are neglected. The relevant cases are examined and the corresponding solutions are categorized. They include nonmonotone profiles, multiple shocks, and self-developing stable saturation plateaus. Numerical results are presented that illustrate the mathematical analysis. Finally, we discuss the implication of our findings in the context of available experimental results.Deutsche Forschungsgemeinschaft, Grant/AwardNumber: 327154368; Technische-Universitat Dortmund; Universiteit Hasselt, Grant/AwardNumber: BOF17BL04; Fonds Wetenschappelijk Onderzoek, Grant/Award Numbers: G051418N, G0G1316N; Darcy Center, Eindhoven University ofTechnology and Utrecht University; Cluster of Excellence in Simulation Technology, Grant/AwardNumber: (EXC310/2); Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Grant/Award Number: 14CSER016Mitra, K (reprint author), Tech Univ Dortmund, Fac Math, Vogelpothsweg 87, D-44227 Dortmund, Germany.
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Investigation of Different Throat Concepts for Precipitation Processes in Saturated Pore-Network Models
No full textThe development of reliable mathematical models and numerical discretization methods is important for the understanding of salt precipitation in porous media, which is relevant for environmental problems like soil salinization. Models on the pore scale are necessary to represent local heterogeneities in precipitation and to include the influence of solution-air-solid interfaces. A pore-network model for saturated flow, which includes the precipitation reaction of salt, is presented. It is implemented in the open-source simulator DuMuX\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\end{document}. In this paper, we restrict ourselves to one-phase flow as a first step. Since the throat transmissibilities determine the flow behaviour in the pore network, different concepts for the decreasing throat transmissibility due to precipitation are investigated. We consider four concepts for the amount of precipitation in the throats. Three concepts use information from the adjacent pore bodies, and one employs a pore-throat model obtained by averaging the resolved pore-scale model in a thin-tube. They lead to different permeability developments, which are caused by the different distribution of the precipitate between the pore bodies and throats. We additionally apply two different concepts for the calculation of the transmissibility. One obtains the precipitate distribution from analytical assumptions, the other from a geometric minimization principle using a phase-field evolution equation. The two concepts do not show substantial differences for the permeability development as long as simple pore-throat geometries are used. Finally, advantages and disadvantages of the concepts are discussed in the context of the considered physical problem and a reasonable effort for the implementation and computational costs. Presentation of a pore-network model for single-phase flow with salt precipitation including pore-space alterationsDifferent concepts to calculate the amount of precipitation in throats and the throat transmissibility are presentedBetween the concepts large differences in the permeability and precipitation distribution are observed in the networkFunding
Open Access funding enabled and organized by Projekt DEAL. This work was fnancially supported by the German Research Foundation (DFG), within the Collaborative Research Center on InterfaceDriven Multi-Field Processes in Porous Media (SFB 1313, Project Number 327154368).
Acknowledgements
This work was fnancially supported by the German Research Foundation (DFG), within the Collaborative Research Center on Interface-Driven Multi-Field Processes in Porous Media (SFB 1313, Project Number 327154368). This study was supported by the Special Research Fund (BOF) of Hasselt University, Project BOF22KV03
Estimation of Capillary‐Associated NAPL‐Water Interfacial Areas for Unconsolidated Porous Media by Kinetic Interface Sensitive (KIS) Tracer Method
No full textAbstract
By employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass‐bead materials and three natural porous media systems to quantitatively characterize the influence of the porous‐medium grain‐, pore‐size and texture on the specific capillary‐associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy‐scale numerical model. Linear relations between the specific capillary‐associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary‐associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary‐associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary‐associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.Key Points
The capillary‐associated interfacial area is measured with the kinetic interface sensitive tracer method in six unconsolidated porous media
It is found the maximum specific capillary‐associated interfacial area is linearly correlated to the inverse mean grain diameters
The higher capillary‐associated interfacial area is found in natural porous media due to surface roughness and irregular grain shapesAbstract
By employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass‐bead materials and three natural porous media systems to quantitatively characterize the influence of the porous‐medium grain‐, pore‐size and texture on the specific capillary‐associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy‐scale numerical model. Linear relations between the specific capillary‐associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary‐associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary‐associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary‐associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.Key Points
The capillary‐associated interfacial area is measured with the kinetic interface sensitive tracer method in six unconsolidated porous media
It is found the maximum specific capillary‐associated interfacial area is linearly correlated to the inverse mean grain diameters
The higher capillary‐associated interfacial area is found in natural porous media due to surface roughness and irregular grain shapesDeutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Hydraulic fracturing in unconventional gas reservoirs: risks in the geological system part 1
No full textHydraulic fracturing of unconventional gas reservoirs rapidly developed especially in the USA to an industrial scale during the last decade. Potential adverse effects such as the deterioration of the quality of exploitable groundwater resources, areal footprints, or even the climate impact were not assessed. Because hydraulic fracturing has already been practised for a long time also in conventional reservoirs, the expansion into the unconventional domain was considered to be just a minor but not a technological step, with potential environmental risks. Thus, safety and environmental protection regulations were not critically developed or refined. Consequently, virtually no baseline conditions were documented before on-site applications as proof of evidence for the net effect of environmental impacts. Not only growing concerns in the general public, but also in the administrations in Germany promoted the commissioning of several expert opinions, evaluating safety, potential risks, and footprints of the technology in focus. The first two publications of the workgroup "Risks in the Geological System" of the independent "Information and Dialogue process on hydraulic fracturing" (commissioned by ExxonMobil Production Deutschland GmbH) comprises the strategy and approaches to identify and assess the potential risks of groundwater contamination of the exploitable groundwater system in the context of hydraulic fracturing operations in the Munsterland cretaceous basin and the Lower Saxony Basin, Germany. While being specific with respect to local geology and the estimation of effective hydraulic parameters, generalized concepts for the contamination risk assessment were developed. The work focuses on barrier effectiveness of different units of the overburden with respect to the migration of fracking fluids and methane, and considers fault zones as potential fluid pathway structures
Hydraulic fracturing in unconventional gas reservoirs : risks in the geological system, part 2
No full textHydraulic fracturing is a method used for the production of unconventional gas resources. Huge amounts of so-called fracturing fluid (10,000-20,000 m(3)) are injected into a gas reservoir to create fractures in solid rock formations, upon which mobilised methane fills the pore space and the fracturing fluid is withdrawn. Hydraulic fracturing may pose a threat to groundwater resources if fracturing fluid or brine can migrate through fault zones into shallow aquifers. Diffuse methane emissions from the gas reservoir may not only contaminate shallow groundwater aquifers, but also escape into the atmosphere where methane acts as a greenhouse gas. The working group "Risks in the Geological System" as part of ExxonMobil's hydrofracking dialogue and information dissemination processes was tasked with the assessment of possible hazards posed by migrating fluids as a result of hydraulic fracturing activities. In this work, several flow paths for fracturing fluid, brine and methane are identified and scenarios are set up to qualitatively estimate under what circumstances these fluids would leak into shallower layers. The parametrisation for potential hydraulic fracturing sites in North Rhine-Westphalia and Lower Saxony (both in Germany) is derived from literature using upper and lower bounds of hydraulic parameters. The results show that a significant fluid migration is only possible if a combination of several conservative assumptions is met by a scenario
Novel approach for modeling kinetic interface-sensitive (KIS) tracers with respect to time-dependent interfacial area change for the optimization of supercritical carbon dioxide injection into deep saline aquifers
No full textTracer methods represent techniques commonly used for the characterization and for the monitoring of transport processes in geo-reservoirs (e.g., CO2 storage). The current short communication addresses the development of a conceptual, mathematical and numerical model for a new tracer class (KIS tracers, Schaffer et al., 2013) useful for the characterization of fluid fluid interfacial areas during supercritical CO2 injection into deep saline aquifers. This tracer type has the potential to quantify the amount of fluid fluid interfacial areas, important for the quantification of reactions at the fluid interface, which can implicitly lead to optimized injection strategies, a better assessment of the extent of the CO2 plume and of the storage efficiency. The presented modeling approach overcomes the drawback of the current standard multiphase multicomponent models, which ignore kinetics of mass transfer over the interfacial area between the CO2 and brine and consider only the volumetric fraction of the fluids or their mass and molar fractions, respectively. In this model, the concept of a specific interfacial area obtained from pore network modeling is used to complement the constitutive relationships between capillary pressure and saturation. It is a two-phase four component flow and transport model with a kinetic mass transfer of tracers between the two fluids and taking the dissolution of CO2 in brine into account. Two numerical simulation scenarios are shown as examples for the design of experimental work in laboratory and eventually in the field. The modeling approach follows the assumptions of previous experimental work (Schaffer et al., 2013). Their implications are investigated by sensitivity analyses to narrow the physical range of reaction rates for further experiments and molecular tracer design. Both examples indicate that the tracer concentration is sensitive with respect to the interfacial area and, therefore, KIS tracer utilization both in the lab and in the field appear to be feasible for implementation. (C) 2014 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evaporation dynamics and energy partitioning over drying porous surfaces - from pores to landscapes
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