| 1. |
- Babakhani, Peyman, et al.
(författare)
-
Comparison of a new mass-concentration, chain-reaction model with the population-balance model for early- and late-stage aggregation of shattered graphene oxide nanoparticles
- 2019
-
Ingår i: Colloids and Surfaces A. - : ELSEVIER. - 0927-7757 .- 1873-4359. ; 582
-
Tidskriftsartikel (refereegranskat)abstract
- Aggregation as an essential mechanism impacting nanoparticle (NP) functionality, fate, and transport in the environment is currently modelled using population-balance equation (PBE) models which are computationally expensive when combined with other continuum-scale reactive transport models. We propose a new simple mass-concentration-based, chain-reaction modelling (CRM) framework to alleviate computational expenses of PBE and potentially to facilitate combination with other fate, transport, and reaction models. Model performance is compared with analytical PBE solution and a standard numerical PBE technique (fixed pivot, FP) by fitting against experimental data (i.e., hydrodynamic diameter and derived count rate of dynamic light scattering used as a representative of mass concentration) for early- and late-stage, aggregation of shattered graphene oxide (SGO) NP across a broad range of solution chemistries. In general, the CRM approach demonstrates a better match with the experimental data with a mean Nash-Sutcliffe model efficiency (NSE) coefficient of 0.345 than the FP model with a mean NSE of 0.29. Comparing model parameters (aggregation rate constant and fractal dimension) obtained from fitting CRM and FP to the experimental data, similar trends or ranges are obtained between the two approaches. Computationally, the modified CRM is an order-of-magnitude faster than the FP technique, suggesting that it can be a promising modelling framework for efficient and accurate modelling of NP aggregation. However, in the scope of this study, reaction rate coefficients of the CRM have been linked to collision frequencies based on simplified and empirical relationships which need improvement in future studies.
|
|
| 2. |
- Babakhani, Peyman, et al.
(författare)
-
Modified MODFLOW-based model for simulating the agglomeration and transport of polymer-modified Fe0 nanoparticles in saturated porous media
- 2018
-
Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 25:8, s. 7180-7199
-
Tidskriftsartikel (refereegranskat)abstract
- The solute transport model MODFLOW has become a standard tool in risk assessment and remediation design. However, particle transport models that take into account both particle agglomeration and deposition phenomena are far less developed. The main objective of the present study was to evaluate the feasibility of adapting the standard code MODFLOW/MT3D to simulate the agglomeration and transport of three different types of polymer-modified nanoscale zerovalent iron (NZVI) in one-dimensional (1-D) and two-dimensional (2-D) saturated porous media. A first-order decay of the particle population was used to account for the agglomeration of particles. An iterative technique was used to optimize the model parameters. The model provided good matches to 1-D NZVI-breakthrough data sets, with R 2 values ranging from 0.96 to 0.99, and mass recovery differences between the experimental results and simulations ranged from 0.1 to 1.8 %. Similarly, simulations of NZVI transport in the heterogeneous 2-D model demonstrated that the model can be applied to more complicated heterogeneous domains. However, the fits were less good, with the R 2 values in the 2-D modeling cases ranging from 0.75 to 0.95, while the mass recovery differences ranged from 0.7 to 6.5 %. Nevertheless, the predicted NZVI concentration contours during transport were in good agreement with the 2-D experimental observations. The model provides insights into NZVI transport in porous media by mathematically decoupling agglomeration, attachment, and detachment, and it illustrates the importance of each phenomenon in various situations.
|
|
| 3. |
- Basirat, Farzad, et al.
(författare)
-
Experimental and modeling investigation of CO2 flow and transport in a coupled domain of porous media and free flow
- 2015
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 42, s. 461-470
-
Tidskriftsartikel (refereegranskat)abstract
- A solid understanding of the transport mechanisms of gaseous CO2 near the land surface is necessary for developing reliable monitoring techniques and predictive models for possible CO2 leakage from deep underground storage. The objective of this work has been to develop an experimental method along with a simulation model for gaseous CO2 flow and transport in a system including both the porous media and the free air space above it. The experimental system consisted of a two-dimensional bench scale rectangular sandbox containing homogenous sand with an open space of still air above it. Gaseous CO2 was injected in different modes and the CO2 breakthrough was measured on specified ports in the system by using CO2 concentration sensors. A numerical model combining the gas flow in the porous medium and the free flow region was developed and used to model the experimental data. In this quest, the Discontinuous One-Domain approach was selected for modeling transport between the free flow and porous regions. The observed and simulated CO2 breakthrough curves both in the dried sand and in the free flow matched very well in the case of uniform injection and satisfactorily even in the case of point injection. Consequently, it seems that the model reasonably matches the observed data in the cases where the boundary condition is well defined. In summary, our results show that the developed experimental setup provides capability to study gaseous CO2 flow and transport in a coupled porous medium - free flow system and that our modeling approach is able to predict the flow and transport in this system with good accuracy.
|
|
| 4. |
- Basirat, Farzad, et al.
(författare)
-
Modeling Gas Transport in the Shallow Subsurface in Maguelone Field Experiment
- 2013
-
Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; , s. 337-345
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, TOUGH2/EOS7CA model is used to simulate the shallow injection-monitoring experiment carried outat Maguelone, France, during 2012 and 2013. The ultimate objective of the work is to improve our understanding ofgas transport in the shallow subsurface as well as to develop and validate the model to monitor it. This workrepresents first results towards modelling the nitrogen and CO2 injection experiments carried out. The pressure datafrom the first injection experiments in summer 2012 is used as basis for comparison. Work is presently going on toincorporate the experimental data into the numerical simulation further.
|
|
| 5. |
- Basirat, Farzad, et al.
(författare)
-
Modeling gas transport in the shallow subsurface in the Maguelone field experiment
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Developing reliable monitoring techniques to detect and characterize CO2 leakage in shallow subsurface is necessary for the safety of any GCS project. To test different monitoring techniques, shallow injection-monitoring experiment have and are being carried out at the Maguelone, along the Mediterranean lido of the Gulf of Lions, near Montpellier, France. This experimental site was developed in the context of EU FP7 project MUSTANG and is documented in Lofi et al. (2012). Gas injection experiments are being carried out and three techniques of pressure, electrical resistivity and seismic monitoring have been used to detect the nitrogen and CO2 release in the near surface environment. In the present work we use the multiphase and multicomponent TOUGH2/EOS7CA model to simulate the gaseous nitrogen and CO2 transport of the experiments carried out so far. The objective is both to gain understanding of the system performance based on the model analysis as well as to further develop and validate modelling approaches for gas transport in the shallow subsurface, against the well-controlled data sets. Numerical simulation can also be used for the prediction of experimental setup limitations. We expect the simulations to represent the breakthrough time for the different tested injection rates. Based on the hydrogeological formation data beneath the lido, we also expect the vertical heterogeneities in grain size distribution create an effective capillary barrier against upward gas transport in numerical simulations.
|
|
| 6. |
- Basirat, Farzad, et al.
(författare)
-
Numerical modelling of CO2 injection at small-scale field experimental site in Maguelone, France
- 2016
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 54, s. 200-210
-
Tidskriftsartikel (refereegranskat)abstract
- To evaluate the performance of downhole and surface geophysical monitoring methods, a series of shallow gas injection-monitoring experiments has been performed in a coastal saline aquifer at Maguelone, France. The recorded data include pressure measurements with a Westbay multilevel completion and CO2 saturation at an observation well derived from electrical resistivity with a modified Waxman-Smits (MWS) model. In this work, the aim is to develop a simulation model capturing the gas transport behavior and consistent with field data. For this purpose, the simulation of the CO2 injection experiment is carried out with two conceptual models, a homogeneous model and a heterogeneous model treated with multiple realization Monte Carlo simulations. Numerical simulator TOUGH2 with the equation of state module EOS7C is used for the simulations. Comparison of the model results with field data suggests that the pressure responses are captured with relatively good accuracy. Similarly, the model also provides an overall reasonable agreement and correct order of magnitude for predicted gas saturation values. However, as the heterogeneity pattern in the field data remains largely unknown, the model predictions can only be used to capture the mean behavior as well as to provide insights into how heterogeneity can influence the system behavior, by means of sensitivity analyses of the influence of heterogeneities on individual realizations.
|
|
| 7. |
|
|
| 8. |
- Basirat, Farzad, et al.
(författare)
-
Small scale laboratory design investigation of leakage of gaseous CO2 through heterogeneous subsurface system
- 2012
-
Konferensbidrag (refereegranskat)abstract
- The technology for geological sequestration of carbon dioxide has been developed to reduce the CO2 emissions into the atmosphere from the use of fossil fuels in power generation and other industries. One of the main concerns associated with the geological storage is the possible leakage of CO2 into the shallow aquifers, for which effective detection methods are needed. The processes related to the spreading and trapping of CO2 in the reservoir formation and in supercritical conditions have received major attention and form the basis of understanding of CO2 trapping processes. Some of the CO2 may, however, also leak to the upper layers of the rock and all the way to land surface through faults and imperfections in the seal. A proper understanding and capability to detect such leaks is essential for a safe performance of any storage operation. This, in turn, involves a proper understanding of the processes related to the transport of gaseous CO2 in the nearsurface conditions, a topic that has received considerably less attention. The objective of this study is to analyze the transport and migration of gaseous CO2 in heterogeneous porous media, in controlled laboratory conditions. CO2 may reach the unsaturated zone by different leak mechanisms which may subsequently affect how and where it can be detected by leakage monitoring program. These mechanisms include exsolution from CO2 supersaturated water and continuous bubbling or gas flow along a leakage path. Below the water table, gaseous CO2 can also be trapped under capillary barriers. However, as more CO2 is supplied by leakage from below the water table, the pressure may at some point exceed the entry pressure of the barrier leading to a leak event. Similarly, fluctuations in the water table may also produce leak events of temporarily trapped CO2. In the unsaturated zone, the CO2 is heavier than air and may accumulate below ground surface and move laterally. The presence of heterogeneity influences both the movement and detectability of the CO2. Our laboratory experiment is designed and implemented for measuring CO2 distribution in time and space through the heterogeneous porous material. The CO2 concentrations through the domain are measured by using sensitive gas sensors. To better understand the consequences of CO2 leakage and how it can be detected, this study presents a conceptual model together with the design and setup of an experimental system to understand the transport, trapping and detectability of gaseous CO2 in a heterogeneous shallow geological system.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- Envall, Ida, et al.
(författare)
-
Existing evidence related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones : a systematic map
- 2023
-
Ingår i: Environmental Evidence. - : Springer Nature. - 2047-2382. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: In Sweden there are nearly one million soil-based on-site wastewater treatment systems (OWTSs). OWTSs may contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). Hence, in certain cases, a high P removal rate (up to 90%) of OWTSs is required by Swedish authorities. Since these requirements may have costly consequences to property owners, it is debated whether they are too strict. In this debate, it is often claimed that the soil retention of P occurring in the natural environments may be underestimated by authorities. Soil retention is the inhibition of the transport of P through the ground, due to different chemical, physical and biological processes occurring there. These processes make the P transport slower, which may reduce the unwanted impact on receiving water bodies. However, the efficiency of soil retention of P remains unclear. The objective of this systematic map was to collect, code, organise and elucidate the relevant evidence related to the topic, to be able to guide stakeholders through the evidence base, and to support future research synthesising, commissioning, and funding. The systematic map was carried out in response to needs declared by the Swedish Agency for Marine and Water Management but the conclusions should be valid for a wider range of countries across boreo-temperate regions.Methods: Searches were made for peer-reviewed and grey literature using bibliographic databases, search engines, specialist websites, and stakeholder contacts. The references were screened for relevance according to a predefined set of eligibility criteria. A detailed database of the relevant studies was compiled. Data and metadata that enable evaluation and discussion of the character and quality of the evidence base were extracted and coded. Special focus was placed on assessing if existing evidence could contribute to policy and practice decision making. Descriptive information about the evidence base was presented in tables and figures. An interactive evidence atlas and a choropleth were created, displaying the locations of all studies.Review findings: 234 articles out of 10,797 screened records fulfilled the eligibility criteria. These articles contain 256 studies, performed in the field or in the laboratory. Six different study types were identified, based on where the measurements were conducted. Most studies, including laboratory studies, lack replicates. Most field studies are observational case studies.Conclusions: It is not possible to derive valid generic measures of the efficiency of soil retention of P occurring in the natural soil environment from available research. Neither does the evidence base allow for answering the question of the magnitude of the potential impact of OWTSs on the P concentration in recipients on a general basis, or under what conditions OWTSs generally have such an impact. A compilation of groundwater studies may provide examples of how far the P may reach in x years, but the number of groundwater studies is insufficient to draw any general conclusions, given the complexity and variability of the systems. Future research should strive for replicated study designs, more elaborate reporting, and the establishment of a reporting standard.
|
|
| 13. |
- Envall, Ida, et al.
(författare)
-
What evidence exists related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones? : A systematic map protocol
- 2020
-
Ingår i: Environmental Evidence. - : BMC. - 2047-2382. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background Soil-based on-site wastewater treatment systems (OWSs) are suspected to contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). However, along the flow path between the facilities and surface waters, different processes contribute to delay the transport of phosphorus through the ground. This may reduce the unwanted impact on receiving water bodies. However, the strength and significance of this so-called soil retention remains unclear. In Sweden, there are nearly one million OWSs. To protect surface waters, a high P removal rate (up to 90%) is often required by the local municipalities. However, since these requirements may have costly consequences to property owners, it is debated as to whether they are too strict. In this debate, it is often claimed that the retention of P occurring in natural environments may be underestimated by authorities. Accordingly, there is a need for a scrutiny of the available evidence related to soil retention of phosphorus from OWSs. This is the objective of the planned systematic map. Focus will be on boreal and temperate climate zones. Methods Searches will be made for peer-reviewed articles and grey literature using bibliographic databases, search engines, specialist websites and stakeholder contacts. The references will be screened for relevance according to a predefined set of eligibility criteria. At stage one, after testing and clarifying the eligibility criteria, the references will be single-screened based on title and abstract. At stage two, potentially relevant references will be screened in full-text independently by two reviewers. We will compile a detailed database of the relevant studies. Moreover, a narrative report will be produced, describing the research landscape in general terms. This will be carried out with a conceptual model, describing the processes involved in P retention in natural environments, as a foundation. It will be discussed where the respective studies/study types fit into the conceptual model, and also evaluated how each study/study type can be related to the overarching question of eutrophication. Moreover, we will describe identified knowledge gaps that warrant further primary research effort, as well as identified knowledge clusters that could be suitable for systematic reviews.
|
|
| 14. |
|
|
| 15. |
- Fagerlund, Fritjof, et al.
(författare)
-
A partially coupled, fraction-by-fraction modelling approach to the subsurface migration of gasoline spills
- 2007
-
Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 89:3-4, s. 174-198
-
Tidskriftsartikel (refereegranskat)abstract
- The subsurface spreading behaviour of gasoline, as well as several other common soil- and groundwater pollutants (e.g. diesel, creosote), is complicated by the fact that it is a mixture of hundreds of different constituents, behaving differently with respect to e.g. dissolution, volatilisation, adsorption and biodegradation. Especially for scenarios where the non-aqueous phase liquid (NAPL) phase is highly mobile, such as for sudden spills in connection with accidents, it is necessary to simultaneously analyse the migration of the NAPL and its individual components in order to assess risks and environmental impacts.Although a few fully coupled, multi-phase, multi-constituent models exist, such models are highly complex and may be time consuming to use. A new, somewhat simplified methodology for modelling the subsurface migration of gasoline while taking its multi-constituent nature into account is therefore introduced here. Constituents with similar properties are grouped together into eight fractions. The migration of each fraction in the aqueous and gaseous phases as well as adsorption is modelled separately using a single-constituent multi-phase flow model, while the movement of the free-phase gasoline is essentially the same for all fractions. The modelling is done stepwise to allow updating of the free-phase gasoline composition at certain time intervals. The output is the concentration of the eight different fractions in the aqueous, gaseous, free gasoline and solid phases with time.The approach is evaluated by comparing it to a fully coupled multi-phase, multi-constituent numerical simulator in the modelling of a typical accident-type spill scenario, based on a tanker accident in northern Sweden. Here the PCFF method produces results similar to those of the more sophisticated, fully coupled model. The benefit of the method is that it is easy to use and can be applied to any single-constituent multi-phase numerical simulator, which in turn may have different strengths in incorporating various processes. The results demonstrate that the different fractions have significantly different migration behaviours and although the methodology involves some simplifications, it is a considerable improvement compared to modelling the gasoline constituents completely individually or as one single mixture.
|
|
| 16. |
|
|
| 17. |
- Fagerlund, Fritjof, et al.
(författare)
-
Comparison of relative permeability-fluid saturation-capillary pressure relations in the modelling of non-aqueous phase liquid infiltration in variably saturated, layered media
- 2006
-
Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 29:11, s. 1705-1730
-
Tidskriftsartikel (refereegranskat)abstract
- The characteristic functions relating relative permeabilities and capillary pressures to fluid saturations (kr–S–Pc models) are of great importance for the modelling of sub-surface multi-phase flow and transport. In order to test their performance and to identify their important parameters, four well-known three-phase kr–S–Pc models have been tested against published experimental data on non-aqueous phase liquid (NAPL) migration in the unsaturated zone. Both homogenous systems and systems with embedded heterogeneities have been analysed. The results show that although there are differences between predictions based on the different models, all models exhibit some common problems and it is not obvious that any one model is more accurate than the other three. However, with the inclusion of a non-linear NAPL tortuosity factor, both the Brooks–Corey–Burdine and van Genuchten–Mualem models yield excellent fits to experimental data. For NAPLs with non-zero spreading coefficients no exact theory currently exists for scaling two-phase capillary pressure–saturation functions to three-phase systems. Different ways of applying the Parker et al. [Parker JC, Lenhard RJ, Kuppusamy T. A parametric model for constitutive properties governing multi-phase flow in porous media. Water Resour Res 1987;23:618–24] scaling method have therefore been tested. It was found that since the NAPL–gas capillary pressure function has the strongest influence on NAPL migration, the scaling procedure should focus on accuracy in this function.
|
|
| 18. |
|
|
| 19. |
- Fagerlund, Fritjof, et al.
(författare)
-
Design of a two-well field test to determine in situ residual and dissolution trapping of CO2 applied to the Heletz CO2 injection site
- 2013
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 19, s. 642-651
-
Tidskriftsartikel (refereegranskat)abstract
- Field testing is a critical step to improve our knowledge on in situ-trapping mechanisms of CO2 injected in geological formations and their relative importance. In this study, we present a two-well test sequence aimed at quantifying field values of both residual and dissolution trapping of CO2. Then, we apply it to the Heletz experimental CO2 injection site, using numerical modelling. The sequence includes a hydraulic test to measure residual scCO(2) saturation and a novel tracer technique, together with measurements of abstracted fluid compositions for quantification of the rate of CO2 dissolution in the reservoir. The proposed tracer technique uses a tracer with negligible aqueous solubility, which is injected with the scCO(2) and enriched in the scCO(2) phase as CO2 dissolves. We show that this tracer can provide direct information about the dissolution of mobile scCO(2). We also show that the rate of abstracted dissolved CO2 can be used to predict the total rate of CO2 dissolution, provided that the amount of dissolved CO2 in the formation stabilizes, and that this can be achieved with the proposed abstraction scheme. We conclude that the combination of these measurements is a promising tool for detailed field-scale characterization of residual and dissolution trapping processes.
|
|
| 20. |
|
|
| 21. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Dissolution Of A Spatially Variable Non-Aqueous Phase Liquid Source: Experimental Study And Model Devolpment
- 2009
-
Ingår i: PROCEEDINGS, TOUGH Symposium 2009.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mass transfer from subsurface occurrences of non-aqueous phase liquids (NAPLs) to the surrounding groundwater is a key process, both for persistent contamination problems originating from organic liquid sources, and for dissolution trapping in geological CO2 sequestration. While the dissolution typically is governed by processes that occur on very small scales (i.e., the pore scale), there is a need to model the mass transfer coupled to transport of dissolved chemical components over field scales that are several orders of magnitude larger. Upscaled models, linking the small-scale characteristics to the total mass transfer from sources of dissolved chemicals, are therefore needed. Well-controlled laboratory experiments conducted in test cells allow for the generation of accurate data to validate such upscaling methods before applying them to much more complex field systems. Following this approach, a set of experiments were conducted in a two-dimensional sand tank, wherethe dissolution of a spatially variable, 5 cm by 5 cm DNAPL tetrachloroethene (PCE) source was carefully monitored in space and time. With a resolution of 0.2´0.2 cm, NAPL saturations were measured using x-ray attenuation techniques at approximately 1,000 individual pixels in the source zone. By continuously measuring the NAPL saturations, the temporal evolution of DNAPL mass loss by dissolution to groundwater could be measured at each pixel. The rate of dissolution varied spatially and temporally within the source, and was found to be correlated to NAPL morphology, groundwater flow velocity, and position within the source. The dissolution process was modeled using iTOUGH2/T2VOC under assumption of local equilibrium (LE) between the DNAPL and dissolved PCE. A preliminary model of rate-limited (RL) dissolution, based on a Gilland-Sherwood type relation implemented in MODFLOW/RT3D, was also tested. It was found that the LE model could not capture the observed dissolution patterns, although it predicted the total rate of mass transfer well for the given source conditions. The RL model showed potential to better capture the dissolution pattern after further model development. Ongoing work is aimed at addressing these issues by correlating the detailed measurements of NAPL entrapment morphology and local dissolution rates, with the final goal of developing an upscaled model of the total mass transfer from the source zone.
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
- Fagerlund, Fritjof, 1974-
(författare)
-
Experimental and Modelling Studies on the Spreading of Non-Aqueous Phase Liquids in Heterogeneous Media
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-Aqueous Phase Liquids (NAPLs) include commonly occurring organic contaminants such as gasoline, diesel fuel and chlorinated solvents. When released to subsurface environments their spreading is a complex process of multi-component, multi-phase flow. This work has strived to develop new models and methods to describe the spreading of NAPLs in heterogeneous geological media. For two-phase systems, infiltration and immobilisation of NAPL in stochastically heterogeneous, water-saturated media were investigated. First, a methodology to continuously measure NAPL saturations in space and time in a two-dimensional experiment setup, using multiple-energy x-ray-attenuation techniques, was developed. Second, a set of experiments on NAPL infiltration in carefully designed structures of well-known stochastic heterogeneity were conducted. Three detailed data-sets were generated and the importance of heterogeneity for both flow and the immobilised NAPL architecture was demonstrated. Third, the laboratory experiments were modelled with a continuum- and Darcy’s-law-based multi-phase flow model. Different models for the capillary pressure (Pc) – fluid saturation (S) – relative permeability (kr) constitutive relations were compared and tested against experimental observations. A method to account for NAPL immobility in dead-end pore-spaces during drainage was introduced and the importance of accounting for hysteresis and NAPL entrapment in the constitutive relations was demonstrated. NAPL migration in three-phase, water-NAPL-air systems was also studied. Different constitutive relations used in modelling of three-phase flow were analysed and compared to existing laboratory data. To improve model performance, a new formulation for the saturation dependence of tortuosity was introduced and different scaling options for the Pc-S relations were investigated. Finally, a method to model the spreading of multi-constituent contaminants using a single-component multi-phase model was developed. With the method, the migration behaviour of individual constituents in a mixture, e.g. benzene in gasoline, could be studied, which was demonstrated in a modelling study of a gasoline spill in connection with a transport accident.
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
|
|
| 28. |
- Fagerlund, Fritjof, et al.
(författare)
-
Interwell field test to determine in-situ CO2 trapping in a deep saline aquifer : Modelling study of the effects of test design and geological parameters
- 2013
-
Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 40, s. 554-563
-
Tidskriftsartikel (refereegranskat)abstract
- An interwell field test to determine residual phase and dissolution trapping of CO2 is being designed at Heletz, Israel. Effects of test-design options and geological parameters were investigated using numerical modelling. It was found that the interwell distance has large influence on the feasibility of the test both in terms of creation of a zone of residually trapped CO2 and detection of the time when such zone has been created. The optimal distance is site-specific and depends on formation properties. Alternating CO2 and brine injections slightly increased residual trapping, but did not facilitate creation of a well-defined zone of trapping.
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
- Fagerlund, Fritjof, et al.
(författare)
-
Modeling of nonaqueous phase liquid (NAPL) migration in heterogeneous saturated media : Effects of hysteresis and fluid immobility in constitutive relations
- 2008
-
Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 44:3
-
Tidskriftsartikel (refereegranskat)abstract
- The confidence in model predictions for nonaqueous phase liquid (NAPL) transport in stochastically heterogeneous systems is limited. The fundamental approaches as well as the constitutive models have not been sufficiently validated, mainly because of the lack of appropriate experimental data. Recently, Fagerlund et al. (2007a, 2007b) presented a set of well-controlled laboratory data that are used here (1) to analyze the overall performance of the continuum-based approach for predicting two-phase NAPL-water flow in stochastically heterogeneous media and (2) to compare the predictions from different constitutive models. The five models tested were the nonhysteretic Brooks-Corey-Burdine (BCB) and van Genuchten-Mualem (VGM) models, the hysteretic versions of these models (HBCB and HVGM), and the HVGBCB model, a model combining the hysteretic van Genuchten (HVG) P c -S relation and the hysteretic Brooks-Corey-Burdine k r -S relation. Two cases of NAPL migration were considered: a layered system of two homogeneous sands separated by a dipping interface and a system where one of the layers was stochastically heterogeneous. The results showed that the best models could indeed capture the main characteristics of the spreading and immobilization well, demonstrating the validity of the continuum-based approach for this level of stochastic heterogeneity. Implementation of hysteresis was necessary for correct prediction of the observed speed of NAPL migration as well as the amount of immobilized NAPL. The three hysteretic models were similar in their overall prediction error-based performance. The HVGM model produced less overestimation of NAPL saturations but instead underestimated the entrapment at capillary barriers in comparison to the HBCB and HVGBCB models. The HVGM model also overestimated the speed of NAPL migration, which is attributed to its closed-form k r -S function, for which the VG parameter m has to be fitted under the constraint m = 1 − 1/n. The HVG (and VG) P c -S function, in contrast, used a different set of VG parameters produced with no constraint on m, which better represented the pore size distributions of the sands. A relation for partial nonwetting phase immobility during drainage is also presented.
|
|
| 34. |
|
|
| 35. |
|
|
| 36. |
|
|
| 37. |
- Fagerlund, Fritjof, et al.
(författare)
-
Multilevel Monte Carlo methods for computing failure probability of porous media flow systems
- 2016
-
Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 94, s. 498-509
-
Tidskriftsartikel (refereegranskat)abstract
- We study improvements of the standard and multilevel Monte Carlo method for point evaluation of the cumulative distribution function (failure probability) applied to porous media two-phase flow simulations with uncertain permeability. To illustrate the methods, we study an injection scenario where we consider sweep efficiency of the injected phase as quantity of interest and seek the probability that this quantity of interest is smaller than a critical value. In the sampling procedure, we use computable error bounds on the sweep efficiency functional to identify small subsets of realizations to solve highest accuracy by means of what we call selective refinement. We quantify the performance gains possible by using selective refinement in combination with both the standard and multilevel Monte Carlo method. We also identify issues in the process of practical implementation of the methods. We conclude that significant savings in computational cost are possible for failure probability estimation in a realistic setting using the selective refinement technique, both in combination with standard and multilevel Monte Carlo.
|
|
| 38. |
|
|
| 39. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 2. Application to stochastically heterogeneous formations
- 2007
-
Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 483-495
-
Tidskriftsartikel (refereegranskat)abstract
- We performed a series of well-controlled laboratory experimentsinvestigating the infiltration and subsequent immobilizationof nonaqueous-phase liquid (NAPL) in saturated heterogeneousmedia. A system of two distinct aquifer zones separated by adipping interface was considered. Heterogeneity was representedby a spatially correlated random field with known geostatisticalparameters in one zone in combination with a homogenous packingof the other zone. The effects of heterogeneity on NAPL flowand entrapment in each of the two zones were investigated. Thetime-varying NAPL saturations were continuously monitored inspace and the final static entrapment–saturation distributionwas accurately measured. The immobilized-NAPL distribution contributesto plume generation from source zones. The results show thatcapillary barriers produced by the small-scale heterogeneitystrongly influenced the migration paths and the final distributionof NAPL both in space and across different saturation ranges.The NAPL was immobilized both by snap-off to discontinuous blobsand ganglia and by capillary barriers at textural interfaces.Heterogeneity generally increased entrapment, because spatialvariations in capillary properties caused NAPL to be entrappedat higher saturations. Heterogeneity in the finer formationprovided points of entry into this formation where the NAPLsubsequently could spread as the pressure built up. The NAPLwas immobilized at high saturations because high displacementpressures in the fine materials inhibited flow at low saturations.The accessibility for water flow through NAPL occurrences andthereby also the dissolution of NAPL is limited by (i) highentrapped NAPL saturations that decrease the aqueous-phase relativepermeability and (ii) the location of NAPL inside a formationwith low average permeability.
|
|
| 40. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 1. Experimental methods and two-layered reference case
- 2007
-
Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 471-482
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate data to understand the migration and entrapment ofnonaqueous-phase liquids (NAPLs) in heterogeneous formationsare presently lacking. A series of well-controlled laboratoryexperiments were conducted to investigate the infiltration andsubsequent immobilization of dense NAPLs in saturated heterogeneousmedia. The focus of this first study was the development ofa special experimental methodology for measuring the dynamicevolution of a NAPL plume in space and time. To demonstratethe method, a reference case of a two-layered formation consistingof two homogeneous sands separated by a dipping interface ispresented. The dipping formation in the reference case allowsthe study of NAPL behavior at texture interfaces under the influenceof both capillary and gravitational forces. The NAPL-saturationmeasurement methodology, based on a multiple-energy x-ray attenuationtechnique, correctly captured the known injected NAPL volumeas well as the general spreading and entrapment behavior inspace and time. Time-continuous measurements of NAPL saturationsallow the study of the history dependence of entrapped saturations.The Land model predicted the observed trend in the entrapmentbehavior well. The entrapment architecture was parameterizedusing spatial moments and moments of mass distribution at differentsaturations. The general features of the NAPL architecture weresuccessfully characterized by a simultaneous interpretationof these moments, while the domination of discontinuous or continuousNAPL was captured by the ganglia/pool ratio.
|
|
| 41. |
- Fagerlund, Fritjof, et al.
(författare)
-
PCE dissolution and simultaneous dechlorination by nanoscale zero-valent iron particles in a DNAPL source zone
- 2012
-
Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 131:1-4, s. 9-28
-
Tidskriftsartikel (refereegranskat)abstract
- While the capability of nanoscale zero-valent iron (NZVI) to dechlorinate organic compounds in aqueous solutions has been demonstrated, the ability of NZVI to remove dense non-aqueous phase liquid (DNAPL) from source zones under flow-through conditions similar to a field scale application has not yet been thoroughly investigated. To gain insight on simultaneous DNAPL dissolution and NZVI-mediated dechlorination reactions after direct placement of NZVI into a DNAPL source zone, a combined experimental and modeling study was performed. First, a DNAPL tetrachloroethene (PCE) source zone with emplaced NZVI was built inside a small custom-made flow cell and the effluent PCE and dechlorination byproducts were monitored over time. Second, a model for rate-limited DNAPL dissolution and NZVI-mediated dechlorination of PCE to its three main reaction byproducts with a possibility for partitioning of these byproducts back into the DNAPL was formulated. The coupled processes occurring in I he flow cell were simulated and analyzed using a detailed three-dimensional numerical model. It was found that subsurface emplacement of NZVI did not markedly accelerate DNAPL dissolution or the DNAPL mass-depletion rate, when NZVI at a particle concentration of 10 g/L was directly emplaced in the DNAPL source zone. To react with NZVI the DNAPL PCE must first dissolve into the groundwater and the rate of dissolution controls the longevity of the DNAPL source. The modeling study further indicated that faster reacting particles would decrease aqueous contaminant concentrations but there is a limit to how much the mass removal rate can be increased by increasing the dechlorination reaction rate. To ensure reduction of aqueous contaminant concentrations, remediation of DNAPL contaminants with NZVI should include emplacement in a capture zone down-gradient of the DNAPL source.
|
|
| 42. |
|
|
| 43. |
|
|
| 44. |
- Hedayati, Maryeh, et al.
(författare)
-
Transport and retention of carbon-based engineered and natural nanoparticles through saturated porous media
- 2016
-
Ingår i: Journal of nanoparticle research. - : Springer. - 1388-0764 .- 1572-896X. ; 18:3
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon-based engineered nanoparticles have been widely used due to their small size and unique physical and chemical properties. At the same time, the toxic effects of these nanoparticles on human and fish cells have also been observed; therefore, their release and distribution into the surface and subsurface environment is a subject of concern. The aim of this research is to evaluate and compare the transports and retentions of two types of engineered nanoparticles (multiwalled carbon nanotubes and C-60) and the natural carbon nanoparticles collected from a fire accident. Several laboratory experiments were conducted to observe the transport behavior of nanoparticles through a column packed with silica sand. The column experiments were intended to monitor the effect of ionic strength on transport of nanoparticles as a function of their shapes. It was observed that the mobilities of both types of engineered nanoparticles were reduced with the increasing ionic strength from 1.34 to 60 mM. However, at ionic strengths up to 10.89 mM, spherical nanoparticles were more mobile than cylindrical nanoparticles, but the mobility of the cylindrical nanoparticles became significantly higher than spherical nanoparticles at the ionic strength of 60 mM. In comparison with natural fire-born nanoparticles, both types of engineered nanoparticles were much less mobile under the selected experimental condition in this study. Furthermore, inverse modeling was used to calculate parameters such as attachment efficiency, the longitudinal dispersivity, and capacity of the solid phase for the attachment of nanoparticles. The results indicate that the combination of the shape and the solution chemistry of the NPs are responsible for the transport and the retention of nanoparticles in natural environment; however, fire-burned nanoparticles can be highly mobile at the natural groundwater chemistry.
|
|
| 45. |
- Hellman, Fredrik
(författare)
-
Numerical Methods for Darcy Flow Problems with Rough and Uncertain Data
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We address two computational challenges for numerical simulations of Darcy flow problems: rough and uncertain data. The rapidly varying and possibly high contrast permeability coefficient for the pressure equation in Darcy flow problems generally leads to irregular solutions, which in turn make standard solution techniques perform poorly. We study methods for numerical homogenization based on localized computations. Regarding the challenge of uncertain data, we consider the problem of forward propagation of uncertainty through a numerical model. More specifically, we consider methods for estimating the failure probability, or a point estimate of the cumulative distribution function (cdf) of a scalar output from the model.The issue of rough coefficients is discussed in Papers I–III by analyzing three aspects of the localized orthogonal decomposition (LOD) method. In Paper I, we define an interpolation operator that makes the localization error independent of the contrast of the coefficient. The conditions for its applicability are studied. In Paper II, we consider time-dependent coefficients and derive computable error indicators that are used to adaptively update the multiscale space. In Paper III, we derive a priori error bounds for the LOD method based on the Raviart–Thomas finite element.The topic of uncertain data is discussed in Papers IV–VI. The main contribution is the selective refinement algorithm, proposed in Paper IV for estimating quantiles, and further developed in Paper V for point evaluation of the cdf. Selective refinement makes use of a hierarchy of numerical approximations of the model and exploits computable error bounds for the random model output to reduce the cost complexity. It is applied in combination with Monte Carlo and multilevel Monte Carlo methods to reduce the overall cost. In Paper VI we quantify the gains from applying selective refinement to a two-phase Darcy flow problem.
|
|
| 46. |
|
|
| 47. |
- Kitron-Belinkov, Myra, et al.
(författare)
-
Modeling wellbore and reservoir carbon dioxide flow for the Heletz experiment
- 2012
-
Ingår i: Geophysical Research Abstracts, Vol. 14.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Field carbon dioxide injection experiments are necessary for demonstration, increasing the scientific understandingand quantification of the relevant processes occurring during geological storage in deep saline aquifers. As part ofthe large scale EU-FP7 project MUSTANG, a carbon dioxide injection experiment is to be carried out at the Heletzsite, Israel. Estimating the well head conditions is an important part of planning the experiment and an approach ispresented here for determining wellhead conditions needed to ensure that at least a specified flow rate is providedto the formation, given target layer conditions, while still respecting pressure buildup constraints. The main partof the study combines the multiphase flow in the target layer using the well known TOUGH2/ECO2N model, withthe flow in the injection pipe solving the 1D steady, real gas, augmented Euler equation. The Matching is carriedon in a two-stage process.The second part consists of a transient simulation of the combined well-reservoir flowusing the new T2WELL software for the same parameters. Preliminary conclusions of the comparison of the twostrategies are derived. Sensitivity analyses were carried out with respect to target layer properties and to pipe modelassumptions.
|
|
| 48. |
- Leroy, Philippe, et al.
(författare)
-
Spectral induced polarization of Na-montmorillonite dispersions
- 2017
-
Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 505, s. 1093-1110
-
Tidskriftsartikel (refereegranskat)abstract
- Montmorillonite (Mt) clays have a high specific surface area and surface charge, which confer them remarkable adsorption properties. Nevertheless, their electrochemical and aggregation behavior are not completely elucidated because of the complexity of their microstructural and interfacial properties. In this work, the conductive and dispersive properties of Na-Mt suspensions of weight fractions 0.5-5.2% were investigated for the first time using the spectral induced polarization method. A four-electrode system was used to reduce errors introduced by electrode polarization and contact resistances. Complex conductivity spectra in the low-frequency range of 0.1 Hz to 45 kHz were successfully described using a triple layer model of the basal surface of Mt and a complex conductivity model that considers conduction of the diffuse layer and polarization of the Stern layer. Aggregate size distributions were inferred from inverted relaxation time distributions. We found that the negative and permanent surface charge of the basal plane of Na-Mt controls its quadrature (imaginary) conductivity, which is not very sensitive to pH and salinity (NaCI) in the 100 Hz to 45 kHz frequency range. For lower frequencies, the sudden increase of the quadrature conductivity at the highest salinities was explained by considering coagulation of Na-Mt particles.
|
|
| 49. |
|
|
| 50. |
|
|
