Simulation Of Tracer Transport Research Articles

PoroTwin: A Digital Twin for a FluidFlower Rig

We present a framework for integrated experiments and simulations of tracer transport in heterogeneous porous media using digital twin technology. The physical asset in our setup is a meter-scale FluidFlower rig. The digital twin consists of a traditional physics-based forward simulation tool and a correction technique which compensates for mismatches between simulation results and observations. The latter augments the range of the physics-based simulation and allows us to bridge the gap between simulation and experiments in a quantitative sense. We describe the setup of the physical and digital twin, including data transfer protocols using cloud technology. The accuracy of the digital twin is demonstrated on a case with artificially high diffusion that must be compensated by the correction approach, as well as by simulations in geologically complex media. The digital twin is then applied to control tracer transport by manipulating fluid injection and production in the experimental rig, thereby enabling two-way coupling between the physical and digital twins.

Simulation of experimental synthetic DNA tracer transport through the vadose zone

Although multiple experimental studies have proven the use of free synthetic DNA as tracers in hydrological systems, their quantitative fate and transport, especially through the vadose zone, is still not well understood. Here we simulate the water flow and breakthrough of deuterium (D) and one free synthetic DNA tracer from a 10-day experiment conducted in a transient variably saturated 1m3 10° sloped lysimeter using the HYDRUS-2D software package. Recovery and breakthrough flux of D (97.78%) and the DNA tracer (1.05%) were captured well with the advection-dispersion equation (R2 = 0.949, NSE = 0.937) and the Schijven and Šimůnek two-site kinetic sorption model recommended for virus transport modeling (R2 = 0.824, NSE = 0.823), respectively. The degradation of the DNA tracer was very slow (estimated to be 10% in 10 days), because the “loamy sand” porous media in our lysimeter was freshly crushed basaltic tephra (i.e., crushed rocks) and the microbes and DNase that could potentially degrade DNA in regular soils were rare in our “loamy sand”. The timing of the concentration peaks and the HYDRUS-2D simulated temporal and spatial distribution of DNA in the lysimeter both revealed the role of the solid-water-air contact lines in mobilizing and carrying DNA tracer under the experimental variably saturated transient flow condition. The free DNA was nearly non-selectively transported through the porous media, and showed a slightly early breakthrough, possibly due to a slight effect of anion exclusion or size exclusion. Our results indicate that free DNA have the potential to trace vadose zone water flow and solute/contaminant transport, and to serve as surrogates to trace viral pathogen pollution in soil-water systems. To our knowledge, this study is the first to simulate transport mechanisms of free synthetic DNA tracers through real soil textured porous media under variably saturated transient flow condition.

Direct Numerical Simulation of Stratified Turbulent Flows and Passive Tracer Transport on HPC Systems: Comparison of CPU Architectures

In this paper we assess the influence of CPU architectures commonly used in HPC systems on the efficiency of the implementation of algorithms used for direct numerical simulation (DNS) of turbulent flows. We consider a stably stratified turbulent plane Couette flow as a benchmark problem supplemented with the additional transport of passive substances. The comparison includes the Intel Xeon, AMD Rome x86 CPU architecture processors and the Huawei Kunpeng ARM CPU processor. We discuss the role of memory-oriented optimizations on the efficiency of tracer transport implementation on each platform.

Improving safe sanitation practices using groundwater transport modelling and water quality monitoring data.

In many developing countries, poorly constructed pit latrines are the primary source of groundwater contamination. Approaches are needed to identify site-specific separation distances between domestic wells and pit latrines. In this study, tracer transport simulations are combined with water quality monitoring data to identify separation distances in peri-urban Dar es Salaam. Bivariate correlation and linear regression models were used to find the relationships between (1) simulated tracer and distances from the wells to the nearest pit latrines (2) simulated tracer and observed contaminants (nitrate, E. coli, and total dissolved solids). The results showed a strong correlation between tracer with nitrate and E. coli, with Pearson coefficient (r) values of 0.80 and 0.79, but a weak correlation with total dissolved solids (TDS) (r = 0.23). A strong correlation between tracer and distance for shallow and deep wells (r = -0.96, -0.76) was found. Based on the soil type and aquifer properties in the area, wells must be placed at least 34 m from a pit latrine to minimize contamination. With recent advances in sensor technologies and the availability of low-cost sensors, linking simulated tracer with observed contaminant levels may provide an alternative first approach to quickly assess human health risks associated with groundwater contamination.

Response of water-exchange capacity to human interventions in Jiaozhou Bay, China

Intensive anthropogenic activities, land reclamation, a cross-bay bridge construction, and the correction of Red Island have significantly changed the topography of Jiaozhou Bay (JZB) in northern China over the last decades. To quantify the effects of these modifications on the water-exchange capacity of the bay, the Finite Volume Community Ocean Model was used to calculate basin, regional and local residence time (RT) in the years 1935, 1966, 1986, 2000, 2008, and 2013, covering the periods of significant land reclamation. The bridge construction and a government plan to restore Red Island were also included in additional modelling scenarios. The regional RT increased significantly between 1935 and 1986, by 77% in the northeast, 40% in the west and 56% in the north-bridge regions, concurrent with the largest land reclamation. The regional RT continued to increase from 1986 to 2000 in the northeast and north-bridge regions but decreased slightly from 2000. These patterns can be explained by the general decreasing trend of the tidal prism from 1935 to 2000, up to 66% in the northeast region. A significant decrease in residual currents from 1935 to 1966 probably also contributed to explain this trend. The bridge construction had only a limited effect on regional RT. The restoration of Red Island would have reduced the regional RT in the northeast region from 83 to 60 days. The simulation of tracer transport, and therefore calculation of local RT, was found to be sensitive to the scheme used to formulate the horizontal diffusion coefficient, which should be taking into account when comparing results from different model configurations.

Assessment of Planetary Boundary Layer parametrizations and urban heat island comparison: Impacts and implications for tracer transport.

Accurate simulation of planetary boundary layer height (PBLH) is key to greenhouse gas emission estimation, air quality prediction and weather forecasting. This manuscript describes an extensive performance assessment of several Weather Research and Forecasting (WRF) model configurations where novel observations from ceilometers, surface stations and a flux tower were used to study their ability to reproduce planetary boundary layer heights (PBLH) and the impact that the urban heat island (UHI) has on the modeled PBLHs in the greater Washington, D.C. area. In addition, CO2 measurements at two urban towers were compared to tracer transport simulations. The ensemble of models used 4 PBL parameterizations, 2 sources of initial and boundary conditions and 1 configuration including the building energy parameterization (BEP) urban canopy model. Results have shown low biases over the whole domain and period for wind speed, wind direction and temperature with no drastic differences between meteorological drivers. We find that PBLH errors are mostly positively correlated with sensible heat flux errors, and that modeled positive UHI intensities are associated with deeper modeled PBLs over the urban areas. In addition, we find that modeled PBLHs are typically biased low during nighttime for most of the configurations with the exception of those using the MYNN parametrization and that these biases directly translate to tracer biases. Overall, the configurations using MYNN scheme performed the best, reproducing the PBLH and CO2 molar fractions reasonably well during all hours, thus opening the door to future nighttime inverse modeling.

Non-Fickian dispersivity investigation from numerical simulations of tracer transport in a model double-porosity medium at different saturations

It is generally admitted that dispersivity is an indicator of the heterogeneity scale of porous media. This parameter is assumed to be an intrinsic property which characterizes the dispersive behavior during the transport of a tracer in a porous medium. When the medium is saturated by two fluid phases (water and air), dispersivity depends strongly on saturation. “Double-porosity” medium concept can be attributed to a class of heterogeneous soils and rocks in which a strong contrast in local pore size characteristics is observed. In this work, we characterized non-Fickian dispersivities of a double-porosity medium at different saturations, by performing numerical simulations for a series of one-dimensional experiments of tracer dispersion under different initial and boundary conditions. The physical double-porosity model was composed of solidified clayey spheres, distributed periodically in a more permeable sandy matrix. Using a two-equation macroscopic model, numerical simulations reproduced very well the experimental data, thus allowing to determine the dispersivity for different transport scenarios. For the first time, the existence of a unique dispersivity of a double-porosity medium at a given saturation was demonstrated for different transport scenarios of initial and boundary conditions. The saturation dependence of the dispersivity in the double-porosity medium was established and compared with the trends obtained for the single-porosity soils in previous studies.

Reproducibility of Surface Wind and Tracer Transport Simulations over Complex Terrain Using 5-, 3-, and 1-km-Grid Models

AbstractThe reproducibility of surface wind and tracer transport simulations from high-resolution weather and transport models was studied over complex terrain in wintertime in Japan. The horizontal grid spacing was varied (5-, 3-, and 1-km grids), and radioactive cesium (Cs-137) from the Fukushima nuclear power plant was used as a tracer. Fukushima has complex terrain, such as mountains and valleys. The model results were validated by observations collected from the national networks of the automated meteorological data acquisition system and the hourly air pollution sampling system. The reproducibility depended on the model resolution, topographic complexity, and synoptic weather conditions. Higher model resolution led to higher reproducibility of surface winds, especially in mountainous areas when the Siberian winter monsoon was disturbed. In contrast, the model improvement was negligible or nonexistent over plain/coastal areas when the synoptic field was steady. The statistical scores of the tracer transport simulations often deteriorated as a result of small errors in the plume locations. However, the higher-resolution models advantageously performed better transport simulations in the mountainous areas because of the lower numerical diffusion and higher reproducibility of the mass flux. The reproducibility of the tracer distribution in the valley of the Fukushima mountainous region was dramatically improved with increasing model resolution. In the range of mesoscale model resolutions (commonly 1–10 km), it was concluded that a higher-resolution model is definitely recommended for tracer transport simulations over mountainous terrain.

Global-mean Vertical Tracer Mixing in Planetary Atmospheres. I. Theory and Fast-rotating Planets

Abstract Most chemistry and cloud formation models for planetary atmospheres adopt a one-dimensional (1D) diffusion approach to approximate the global-mean vertical tracer transport. The physical underpinning of the key parameter in this framework, eddy diffusivity K zz , is usually obscure. Here we analytically and numerically investigate vertical tracer transport in a 3D stratified atmosphere and predict K zz as a function of the large-scale circulation strength, horizontal mixing due to eddies and waves and local tracer sources and sinks. We find that K zz increases with tracer chemical lifetime and circulation strength but decreases with horizontal eddy mixing efficiency. We demarcated three K zz regimes in planetary atmospheres. In the first regime where the tracer lifetime is short compared with the transport timescale and horizontal tracer distribution under chemical equilibrium ( ) is uniformly distributed across the globe, global-mean vertical tracer mixing behaves diffusively. But the traditional assumption in current 1D models that all chemical species are transported via the same eddy diffusivity generally breaks down. We show that different chemical species in a single atmosphere should in principle have different eddy diffusion profiles. In the second regime where the tracer is short-lived but is non-uniformly distributed, a significant non-diffusive component might lead to a negative K zz under the diffusive assumption. In the third regime where the tracer is long-lived, global-mean vertical tracer transport is also largely influenced by non-diffusive effects. Numerical simulations of 2D tracer transport on fast-rotating zonally symmetric planets validate our analytical K zz theory over a wide parameter space.

Global-mean Vertical Tracer Mixing in Planetary Atmospheres. II. Tidally Locked Planets

Abstract In Zhang & Showman, we developed an analytical theory of 1D eddy diffusivity K zz for global-mean vertical tracer transport in a 3D atmosphere. We also presented 2D numerical simulations on fast-rotating planets to validate our theory. On a slowly rotating planet such as Venus or a tidally locked planet (not necessarily a slow-rotator) such as a hot Jupiter, the tracer distribution could exhibit significant longitudinal inhomogeneity and tracer transport is intrinsically 3D. Here we study the global-mean vertical tracer transport on tidally locked planets using 3D tracer-transport simulations. We find that our analytical K zz theory in Zhang & Showman is validated on tidally locked planets over a wide parameter space. K zz strongly depends on the large-scale circulation strength, horizontal mixing due to eddies, and waves, and local tracer sources and sinks due to chemistry and microphysics. As our analytical theory predicted, K zz on tidally locked planets also exhibit three regimes. In Regime I where the chemical and microphysical processes are uniformly distributed across the globe, different chemical species should be transported via different eddy diffusivity. In Regime II where the chemical and microphysical processes are nonuniform—for example, photochemistry or cloud formation that exhibits strong day–night contrast—the global-mean vertical tracer mixing does not always behave diffusively. In the third regime where the tracer is long-lived, non-diffusive effects are significant. Using species-dependent eddy diffusivity, we provide a new analytical theory of the dynamical quench points for disequilibrium tracers on tidally locked planets from first principles.

Simulations of Brownian tracer transport in squirmer suspensions

In addition to enabling movement towards environments with favourable living conditions, swimming by microorganisms has also been linked to enhanced mixing and improved nutrient uptake by their populations. Experimental studies have shown that Brownian tracer particles exhibit enhanced diffusion due to the swimmers, while theoretical models have linked this increase in diffusion to the flows generated by the swimming microorganisms, as well as collisions with the swimmers. In this study, we perform detailed simulations based on the force-coupling method and its recent extensions to the swimming and Brownian particles to examine tracer displacements and effective tracer diffusivity in squirmer suspensions. By isolating effects such as hydrodynamic or steric interactions, we provide physical insight into experimental measurements of the tracer displacement distribution. In addition, we extend results to the semi-dilute regime where the swimmer–swimmer interactions affect tracer transport and the effective tracer diffusivity no longer scales linearly with the swimmer volume fraction.

The Open-source Data Inventory for Anthropogenic Carbon dioxide (CO2), version 2016 (ODIAC2016): A global, monthly fossil-fuel CO2 gridded emission data product for tracer transport simulations and surface flux inversions.

The Open-source Data Inventory for Anthropogenic CO2 (ODIAC) is a global high-spatial resolution gridded emission data product that distributes carbon dioxide (CO2) emissions from fossil fuel combustion. The emission spatial distributions are estimated at a 1×1 km spatial resolution over land using power plant profiles (emission intensity and geographical location) and satellite-observed nighttime lights. This paper describes the year 2016 version of the ODIAC emission data product (ODIAC2016) and presents analyses that help guiding data users, especially for atmospheric CO2 tracer transport simulations and flux inversion analysis. Since the original publication in 2011, we have made modifications to our emission modeling framework in order to deliver a comprehensive global gridded emission data product. Major changes from the 2011 publication are 1) the use of emissions estimates made by the Carbon Dioxide Information Analysis Center (CDIAC) at the Oak Ridge National Laboratory (ORNL) by fuel type (solid, liquid, gas, cement manufacturing, gas flaring and international aviation and marine bunkers), 2) the use of multiple spatial emission proxies by fuel type such as nightlight data specific to gas flaring and ship/aircraft fleet tracks and 3) the inclusion of emission temporal variations. Using global fuel consumption data, we extrapolated the CDIAC emissions estimates for the recent years and produced the ODIAC2016 emission data product that covers 2000-2015. Our emission data can be viewed as an extended version of CDIAC gridded emission data product, which should allow data users to impose global fossil fuel emissions in more comprehensive manner than original CDIAC product. Our new emission modeling framework allows us to produce future versions of ODIAC emission data product with a timely update. Such capability has become more significant given the CDIAC/ORNL's shutdown. ODIAC data product could play an important role to support carbon cycle science, especially modeling studies with space-based CO2 data collected near real time by ongoing carbon observing missions such as Japanese Greenhouse Observing SATellite (GOSAT), NASA's Orbiting Carbon Observatory 2 (OCO-2) and upcoming future missions. The ODIAC emission data product including the latest version of the ODIAC emission data (ODIAC2017, 2000-2016), is distributed from http://db.cger.nies.go.jp/dataset/ODIAC/ with a DOI.

Numerical simulation of bedload tracer transport associated with sand bar formation, bank erosion, and channel migration

An understanding of bedload transport processes is an essential research goal for better prediction of river morphology and morphodynamics as well as the transport and fate of sediment-bound materials in river systems. Passive tracer particles have been used widely to monitor bedload transport processes in rivers by measuring the spatiotemporal distribution of the bedload tracers. Here, we propose a numerical model for reproducing the transport of bedload tracers in river systems, more specifically, the behaviours of bedload tracers under the influence of complex river morphodynamics. A two-dimensional morphodynamic model is combined with a flux-based bedload tracer model with use of the active layer approach. The model is applied to a laboratory experiment that demonstrates the transport processes within the channel of bedload tracers supplied from the floodplain. The numerical model effectively reproduces the main features of the experiment, namely, the bedload tracers supplied from the floodplain due to bank erosion deposit onto sand bars developed within the channel. Because the sand bars cause a very long residence time of the bedload tracers within the bed, the transport speed of the tracers is slowed significantly under the influence of bar formation and channel migration.

Modeling tracer flowback in tight oil reservoirs with complex fracture networks

Tight oil reservoirs are commonly developed by a combination of horizontal wells and multistage hydraulic fracturing techniques. The characterization of complex fracture networks after fracturing treatments is a common challenge for unconventional reservoirs. Tracer flowback profiles can reveal a fracture network at an individual stage. However, the numerical simulation of tracer transport in fractured reservoirs usually employs a dual-porosity continuum medium model or describes fractures by an enlarged fracture aperture in a regular grid system that is not capable of modeling a complex fracture network. Especially, the influences of the properties of fracturing fluid and variations in fracture permeability caused by pressure changes on tracer flowback profiles are not investigated.In this paper, a two-phase (water and oil), four-component (oil, water, fracturing fluid and tracer) numerical simulator is developed based on a discrete fracture model for modeling tracer injection and flowback in tight oil reservoirs. With respect to fracture network modeling, the simulator is capable of explicitly modeling an arbitrary distribution of fracture networks with a real fracture aperture by triangular grids. With respect to mechanism consideration, the simulator considers the influences of fracturing fluid and pressure-dependent fracture permeability on tracer flowback profiles. The properties of tracer dispersion and adsorption are also considered in both fractures and matrix. To validate the proposed model, a comparison is performed with the commercial software Eclipse. Sensitivity studies are performed to investigate the influences of parameters on tracer flowback profiles. The presented simulator is applied in the Changji oilfield to characterize individual stages using a stochastic method.Results show that the developed simulator is accurate as with Eclipse. The filed application indicates that the presented simulator can model tracer flowback and production performance. Sensitivity studies show that an increase in permeability modulus and the viscosity of fracturing fluid delays the peak arrival time. An increase in permeability modulus decreases the peak amplitude while an increase in the viscosity of the fracturing fluid increases the peak amplitude. An increase in a dead pore volume and a residual resistance factor has little impact on the peak position and lowers the tails of tracer flowback profiles. The sensitivity studies provide valuable information in characterization of a fracture network using tracer flowback data.

Finite volume schemes for the numerical simulation of tracer transport in plants

Compartmental models can be used for inverse modeling of long distance tracer transport experiments in plants. Such transport models describe axial convection and diffusion as well as exchange between compartments, and are defined by partial differential equations (PDEs). Since for inverse modeling, the forward simulation needs to be evaluated frequently, a fast PDE solver is required. Here, we compare several different finite volumes schemes up to fifth order for spatial discretization with respect to accuracy, computation time and numerical oscillations. The comparison has been performed using initial conditions with varying steepness, and periodic boundary conditions. For time discretization, standard fifth order Runge–Kutta methods are used. For smooth initial conditions, fifth order upwind schemes for spatial discretization yield the most precise and fast solutions. For higher steepness of the initial condition, higher order upwind schemes produce spurious oscillations while flux limiter schemes as well as weighted essentially non-oscillating (WENO) schemes can suppress these oscillations, at the expense of comparably slower convergence rates and higher computation times.

Scaling and Pedotransfer in Numerical Simulations of Flow and Transport in Soils

Flow and transport parameters of soils in numerical simulations need to be defined at the support scale of computational grid cells. Such support scale can substantially differ from the support scale in laboratory or field measurements of flow and transport parameters. The scale dependence of flow and transport parameters essentially precludes the direct use of measured or pedotransfer-estimated parameter values in numerical simulations. The hypothesis of this work was that a support-based scaling law can be introduced that can convert pedotransfer-estimated saturated hydraulic conductivity values into values to be used over grid cells for finite-element-based simulations of water flow and tracer transport in variably saturated soils. A 4-month-long experiment was conducted at the USDA–ARS experimental site where Cl− as a tracer was applied with a pulse of irrigation water and its transport in groundwater and variably saturated shallow coarse-textured soils was monitored in two rows of wells on a daily basis. The HYDRUS-3D software was used to set and calibrate the Richards model for flow simulations and the convective–dispersive equation for transport simulations. Saturated hydraulic conductivity values were estimated with class pedotransfer functions derived from the USDA database containing results of about 1000 measurements in soils of different textures and bulk densities. A power law scaling for the saturated hydraulic conductivity was suggested based on literature data. When only two parameters of the scaling law rather than nine values of hydraulic conductivity from nine soil materials were calibrated, using the scaled saturated hydraulic conductivity values resulted in an accuracy of simulations that was similar to the accuracy of the calibrated model results. Upscaling of pedotransfer-estimated saturated hydraulic conductivities can provide reasonable estimates for numerical flow and transport modeling in variably saturated soils.

Evaluation of Large Eddy Simulation and RANS for Determining Hydraulic Performance of Disinfection Systems for Water Treatment

Reynolds-Averaged Navier–Stokes (RANS) simulation has been demonstrated to be a powerful and efficient approach for conducting numerical assessment of the hydraulic performance of disinfection systems for water treatment at a much lower cost than physical experiments. Recently, large eddy simulation (LES) has been introduced for the first time as a potentially more accurate alternative to RANS for predicting hydraulic performance of disinfection systems such as baffled contactors (Kim et al., 2010, “Large Eddy Simulation of Flow and Tracer Transport in Multichamber Ozone Contactors,” J. Environ. Eng., 136, pp. 22–31). This gives rise to the need to carefully assess RANS and LES in order to understand under which flow characteristics LES should be recommended instead of the less computationally intensive RANS for predicting hydraulic performance of a disinfection system. To that extent, this manuscript presents results from RANS and LES simulations of flow and tracer transport in a laboratory-scale column contactor and a laboratory-scale baffled contactor. Flow fields, residence time distributions, and characteristic residence times are analyzed. LES is shown to be a more reliable strategy than RANS in simulating tracer transport in column contactors due to its ability to better predict the spatial transition to turbulence characterizing the flow. However, in baffled contactors where such transition does not occur and the flow is characterized by a quasi-steady short circuiting jet and dead zones, RANS performs on par with LES.

Simulations of column-averaged CO<sub>2</sub> and CH<sub>4</sub> using the NIES TM with a hybrid sigma-isentropic (σ-θ) vertical coordinate

Abstract. We have developed an improved version of the National Institute for Environmental Studies (NIES) three-dimensional chemical transport model (TM) designed for accurate tracer transport simulations in the stratosphere, using a hybrid sigma-isentropic (σ-θ) vertical coordinate that employs both terrain-following and isentropic parts switched smoothly around the tropopause. The air-ascending rate was derived from the effective heating rate and was used to simulate vertical motion in the isentropic part of the grid (above level 350 K), which was adjusted to fit to the observed age of the air in the stratosphere. Multi-annual simulations were conducted using the NIES TM to evaluate vertical profiles and dry-air column-averaged mole fractions of CO2 and CH4. Comparisons with balloon-borne observations over Sanriku (Japan) in 2000–2007 revealed that the tracer transport simulations in the upper troposphere and lower stratosphere are performed with accuracies of ~5% for CH4 and SF6, and ~1% for CO2 compared with the observed volume-mixing ratios. The simulated column-averaged dry air mole fractions of atmospheric carbon dioxide (XCO2) and methane (XCH4) were evaluated against daily ground-based high-resolution Fourier Transform Spectrometer (FTS) observations measured at twelve sites of the Total Carbon Column Observing Network (TCCON) (Bialystok, Bremen, Darwin, Garmisch, Izaña, Lamont, Lauder, Orleans, Park Falls, Sodankylä, Tsukuba, and Wollongong) between January 2009 and January 2011. The comparison shows the model's ability to reproduce the site-dependent seasonal cycles as observed by TCCON, with correlation coefficients typically on the order 0.8–0.9 and 0.4–0.8 for XCO2 and XCH4, respectively, and mean model biases of ±0.2% and ±0.5%, excluding Sodankylä, where strong biases are found. The ability of the model to capture the tracer total column mole fractions is strongly dependent on the model's ability to reproduce seasonal variations in tracer concentrations in the planetary boundary layer (PBL). We found a marked difference in the model's ability to reproduce near-surface concentrations at sites located some distance from multiple emission sources and where high emissions play a notable role in the tracer's budget. Comparisons with aircraft observations over Surgut (West Siberia), in an area with high emissions of methane from wetlands, show contrasting model performance in the PBL and in the free troposphere. Thus, the PBL is another critical region for simulating the tracer total column mole fractions.

Quantifying Transport Uncertainty in Unsaturated Rock using Monte Carlo Sampling of Retention Curves

We have developed a new Monte Carlo sampling method for simulating flow and transport in unsaturated porous media, characterized by van Genuchten–Mualem constitutive relations. Instead of sampling each individual soil parameter from its probability space and then running Monte Carlo simulations using realizations of rock parameters directly, we calculate retention curves from realizations of rock parameters, take subsamples from these retention curves, and run simulations using parameter realizations corresponding to these selected retention curves. The retention curve subsampling methodology was applied to three‐dimensional simulations of conservative tracer transport beneath Material Disposal Area G at the Los Alamos National Laboratory. Convergence of the proposed sampling method was assessed by comparing statistics of breakthrough curves observed at a compliance boundary with those obtained using between 25 and 1000 Latin hypercube sampling (LHS) Monte Carlo simulations. Our example shows that 25 model runs based on selected retention curves could adequately approximate the results from our assumed truth (1000 LHS Monte Carlo simulations), while LHS alone required in excess of 50 realizations to achieve the same quality result. Another finding from this work is that the median of the breakthrough curves was more meaningful than the arithmetic mean of curves, and the former was nearly identical to the breakthrough curve derived from mean rock properties.

Numerical simulation of tracer transport in the Altmark gas field

The paper presents a modeling strategy as well as simulation results of a designed conservative tracer test in the depleted Altensalzwedel natural gas reservoir in order to know the tracer concentration and breakthrough time at the production wells. Krypton is considered as a suitable tracer. The production wells are located in several hundred meters to a few kilometers away from the injection well. The numerical simulation has been performed by using the newly implemented compositional gas flow module of OpenGeoSys (OGS), a scientific open-source simulator for calculation of coupled geohydraulic (single and multiphase flow), transport (heat and mass transfer), geomechanical and geochemical processes. The tracer breakthrough curves at the production wells show that the breakthrough times vary between 2 and 3 years. The model verification is presented by comparing the OGS results with a one-dimensional analytical solution. The numerical results have been verified by code comparison, additionally.