Numerical strategies for characterizing fractured rock from heat tracer experiments

2020 ◽  
Author(s):  
Delphine Roubinet ◽  
Zitong Zhou ◽  
Daniel Tartakovsky
Keyword(s):  
Density Function ◽  
Test Data ◽  
Fractured Rocks ◽  
Reactive Transport ◽  
Transport Model ◽  
Fracture Network ◽  
Tracer Test ◽  
Transport Processes ◽  
Distributed Temperature Sensing ◽  
Experimental Conditions

<p>Characterization of fractured rocks is a key challenge for optimizing heat harvesting in geothermal systems. The use of heat as a tracer, facilitated by the development of such advanced techniques as active line source (ALS) borehole heating and the distributed temperature sensing (DTS), shows the great potential for characterizing fractured rocks. However, there is so far a limited number of theoretical and numerical studies on how these tests could be used for estimating both fracture-network and rock-matrix properties.</p><p>We use deep neural networks to describe heat tracer test data and demonstrate how the cumulative density function (CDF) or probability density function (PDF) of the heat tracer test data can be deployed in the inversion mode, i.e., to infer the fracture parameters with. Our approach utilizes the methods of distributions, developed previously to estimate the CDF of solute concentration described by a reactive transport model with uncertain parameters and inputs. The method is applied to analyze several synthetic heat tracer test datasets obtained from a particle-based forward model of transport processes in heterogeneous fractured rocks. The study considers alternative representations of fracture networks with a large range of variation of the fracture network properties, as well as several experimental conditions (e.g., ambient/forced thermal and hydraulic conditions, pulse/continuous changes in temperature). This allows us to characterize the system by combining the information from several thermal tests.</p>

scholarly journals Particle-Based Workflow for Modeling Uncertainty of Reactive Transport in 3D Discrete Fracture Networks

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2502 ◽  
Author(s):  
Phuong Thanh Vu ◽  
Chuen-Fa Ni ◽  
Wei-Ci Li ◽  
I-Hsien Lee ◽  
Chi-Ping Lin
Keyword(s):  
Fractured Rocks ◽  
Reactive Transport ◽  
Fracture Network ◽  
Reaction Model ◽  
Transport Processes ◽  
Fracture Networks ◽  
Flow Paths ◽  
Complex Fracture ◽  
Discrete Fracture Networks ◽  
Discrete Fracture

Fractures are major flow paths for solute transport in fractured rocks. Conducting numerical simulations of reactive transport in fractured rocks is a challenging task because of complex fracture connections and the associated nonuniform flows and chemical reactions. The study presents a computational workflow that can approximately simulate flow and reactive transport in complex fractured media. The workflow involves a series of computational processes. Specifically, the workflow employs a simple particle tracking (PT) algorithm to track flow paths in complex 3D discrete fracture networks (DFNs). The PHREEQC chemical reaction model is then used to simulate the reactive transport along particle traces. The study illustrates the developed workflow with three numerical examples, including a case with a simple fracture connection and two cases with a complex fracture network system. Results show that the integration processes in the workflow successfully model the tetrachloroethylene (PCE) and trichloroethylene (TCE) degradation and transport along particle traces in complex DFNs. The statistics of concentration along particle traces enables the estimations of uncertainty induced by the fracture structures in DFNs. The types of source contaminants can lead to slight variations of particle traces and influence the long term reactive transport. The concentration uncertainty can propagate from parent to daughter compounds and accumulate along with the transport processes.

scholarly journals BioRT-Flux-PIHM v1.0: a watershed biogeochemical reactive transport model

2020 ◽  
Author(s):  
Wei Zhi ◽  
Yuning Shi ◽  
Hang Wen ◽  
Leila Saberi ◽  
Gene-Hua Crystal Ng ◽  
...  
Keyword(s):  
Deep Water ◽  
Land Surface ◽  
Reactive Transport ◽  
Transport Model ◽  
Transport Processes ◽  
Spatially Explicit ◽  
Watershed Scale ◽  
Nitrogen And Phosphorus ◽  
Reactive Transport Model ◽  
Component Representation

Abstract. Watersheds are the fundamental Earth surface functioning unit that connects the land to aquatic systems. Existing watershed-scale models typically have physics-based representation of hydrology process but often lack mechanism-based, multi-component representation of reaction thermodynamics and kinetics. This lack of watershed reactive transport models has limited our ability to understand and predict solute export and water quality, particularly under changing climate and anthropogenic conditions. Here we present a recently developed BioRT-Flux-PIHM (BFP) v1.0, a watershed-scale biogeochemical reactive transport model. Augmenting the previously developed RT-Flux-PIHM that integrates land-surface interactions, surface hydrology, and abiotic geochemical reactions (Bao et al., 2017, WRR), the new development enables the simulation of 1) biotic processes including plant uptake and microbe-mediated biogeochemical reactions that are relevant to the transformation of organic matter that involve carbon, nitrogen, and phosphorus; and 2) shallow and deep water partitioning to represent surface and groundwater interactions. The reactive transport part of the code has been verified against the widely used reactive transport code CrunchTope. BioRT-Flux-PIHM v1.0 has recently been applied to understand reactive transport processes in multiple watersheds across different climate, vegetation, and geology conditions. This paper introduces the governing equations and model structure of the code. It also demonstrates examples that simulate shallow and deep water interactions, and biogeochemical reactive transport relevant to nitrate and dissolved organic carbon (DOC). These examples were illustrated in two simulation modes of varying complexity. One is the spatially implicit mode that focuses on processes and average behavior of a watershed. Another is in a spatially explicit mode that includes details of topography, land cover, and soil property conditions. The spatially explicit mode can be used to understand the impacts of spatial structure and identify hot spots of biogeochemical reactions.

Colloidal Transport of Heavy Metals in Natural Subsurface Sediments

2021 ◽  
Author(s):  
Sema Sevinc Sengor
Keyword(s):  
Heavy Metals ◽  
Reactive Transport ◽  
Environmental Remediation ◽  
Transport Model ◽  
Transport Processes ◽  
Subsurface Water ◽  
Colloidal Transport ◽  
Subsurface Sediments ◽  
Oxide Minerals ◽  
The Impact

<p>Colloid particles are widely distributed in the environment. These colloids have recently been gaining significant attention due to their unique characteristics in environmental remediation pertaining to degradation, transformation and immobilization of contaminants in soils and aquifers. On the other hand, once mobilized by subsurface water flow, colloids may pose risks to surface water and groundwater quality as they are effective ‘‘carriers’’ of a variety of common contaminants found in water and soils. Therefore, understanding the transport mechanisms of the colloids and incorporation of colloidal transport processes in reactive transport models are crucial for successful applications of many remediation efforts in the subsurface. Fe (hydr)oxide colloidal compounds have large surface areas and high reactivity, which can lead to spontaneous adsorption of many pollutants. For the successful stabilization of pollutants, it is vital to understand the associated biogeochemical processes, and competitive effects of contaminant sorption onto these colloidal phases. This work focuses on the development of a mechanistic Fe(hydr)oxide based colloid-facilitated reactive transport model which identifies the impact of Fe(hydr)oxide colloids on the stability and mobility of heavy metals (Zn and Pb) in example<strong> </strong>subsurface sediments of Lake Coeur d’Alene (LCdA), USA. Key reactions include the mobilization of heavy metals initially sorbed onto the colloidal Fe(hydr)oxide minerals through microbial reductive dissolution. Precipitation of metal sulfides at depth as a result of biogenic sulfide production is also captured. The simulations compare the biogeochemical cycling of metals considering colloidal vs. immobile phases of Fe(hydr)oxide minerals in the lake sediments.</p>

scholarly journals Mathematical modelling of solute transport in a heterogeneous aquifer

2021 ◽  
Author(s):  
◽  
James Phillip Dommisse
Keyword(s):  
Numerical Model ◽  
Solute Transport ◽  
Test Data ◽  
Hydraulic Properties ◽  
Numerical Models ◽  
Tracer Test ◽  
Transport Processes ◽  
Model Parameters ◽  
Transport Modelling ◽  
Predictive Uncertainty

<p>This study provides a contribution to the understanding of parsimony and predictive uncertainty in the context of groundwater solute transport modelling. The study is unique because the modelling was undertaken using tracer test data from a heterogeneous artificial aquifer whose structure was known to a very high level of detail. The aquifer structure was based on a ‘real life’ Canterbury Plains alluvial aquifer (in New Zealand).  Parsimonious principles were applied by starting with a simple analytical model that assumed homogeneity then progressively adding heterogeneity using numerical models with varying degrees of parameterisation complexity. The results show that increased complexity did not necessarily make the model better at replicating the tracer test data. For example, the outputs from a numerical model that represented heterogeneity using a zone based approach based on the recorded distribution of all 2,907 blocks that comprised the artificial aquifer was little different to a simple numerical model that adopted a homogenous distribution and included a single value of dispersion. Parameterisation of numerical models using ‘pilot points’ provided the most complex representation of heterogeneity and resulted in the best replication of the tracer test data. However, increasing model complexity had its disadvantages such as decreasing parameterisation uniqueness.  The contribution to predictive uncertainty from model parameters and observations was assessed using a linear approach based on Bayes theorem. This approach has been applied to other groundwater modelling studies, but not to solute transport modelling within Canterbury Plains alluvial aquifers or to an artificial aquifer. A unique finding was the reduction in predictive uncertainty along the groundwater flow path. This finding correlated well with the numerical model outputs which showed closer fits to the observation data near the end of the aquifer compared to those near the top of the aquifer where the tracer was injected.  Physical solute transport processes were identified and described as part of the modelling. These included the increase in dispersivity with travel distance and the spatial distribution of the aquifer hydraulic properties. Analytical modelling was a useful tool in identifying physical processes, aquifer characteristics and the variation in aquifer hydraulic properties both spatially and with depth.  An important finding was the value of undertaking multiple modelling approaches. This is because each approach has its own advantages and disadvantageous and by comparing the results of different approaches, the true facts about the aquifer system are made clearer.</p>

scholarly journals A continuum model of multi-phase reactive transport in igneous systems

2019 ◽  
Vol 219 (1) ◽  
pp. 185-222 ◽  
Author(s):  
Tobias Keller ◽  
Jenny Suckale
Keyword(s):  
Reactive Transport ◽  
Model Building ◽  
Transport Model ◽  
Wide Spectrum ◽  
Constitutive Relations ◽  
Mixture Theory ◽  
Transport Processes ◽  
Two Phase ◽  
Macroscopic System ◽  
Special Cases

SUMMARY Multiphase reactive transport processes are ubiquitous in igneous systems. A challenging aspect of modelling igneous phenomena is that they range from solid-dominated porous to liquid-dominated suspension flows and therefore entail a wide spectrum of rheological conditions, flow speeds and length scales. Most previous models have been restricted to the two-phase limits of porous melt transport in deforming, partially molten rock and crystal settling in convecting magma bodies. The goal of this paper is to develop a framework that can capture igneous system from source to surface at all phase proportions including not only rock and melt but also an exsolved volatile phase. Here, we derive an n-phase reactive transport model building on the concepts of Mixture Theory, along with principles of Rational Thermodynamics and procedures of Non-equilibrium Thermodynamics. Our model operates at the macroscopic system scale and requires constitutive relations for fluxes within and transfers between phases, which are the processes that together give rise to reactive transport phenomena. We introduce a phase- and process-wise symmetrical formulation for fluxes and transfers of entropy, mass, momentum and volume, and propose phenomenological coefficient closures that determine how fluxes and transfers respond to mechanical and thermodynamic forces. Finally, we demonstrate that the known limits of two-phase porous and suspension flow emerge as special cases of our general model and discuss some ramifications for modelling pertinent two- and three-phase flow problems in igneous systems.

scholarly journals Mathematical modelling of solute transport in a heterogeneous aquifer

2021 ◽  
Author(s):  
◽  
James Phillip Dommisse
Keyword(s):  
Numerical Model ◽  
Solute Transport ◽  
Test Data ◽  
Hydraulic Properties ◽  
Numerical Models ◽  
Tracer Test ◽  
Transport Processes ◽  
Model Parameters ◽  
Transport Modelling ◽  
Predictive Uncertainty

<p>This study provides a contribution to the understanding of parsimony and predictive uncertainty in the context of groundwater solute transport modelling. The study is unique because the modelling was undertaken using tracer test data from a heterogeneous artificial aquifer whose structure was known to a very high level of detail. The aquifer structure was based on a ‘real life’ Canterbury Plains alluvial aquifer (in New Zealand).  Parsimonious principles were applied by starting with a simple analytical model that assumed homogeneity then progressively adding heterogeneity using numerical models with varying degrees of parameterisation complexity. The results show that increased complexity did not necessarily make the model better at replicating the tracer test data. For example, the outputs from a numerical model that represented heterogeneity using a zone based approach based on the recorded distribution of all 2,907 blocks that comprised the artificial aquifer was little different to a simple numerical model that adopted a homogenous distribution and included a single value of dispersion. Parameterisation of numerical models using ‘pilot points’ provided the most complex representation of heterogeneity and resulted in the best replication of the tracer test data. However, increasing model complexity had its disadvantages such as decreasing parameterisation uniqueness.  The contribution to predictive uncertainty from model parameters and observations was assessed using a linear approach based on Bayes theorem. This approach has been applied to other groundwater modelling studies, but not to solute transport modelling within Canterbury Plains alluvial aquifers or to an artificial aquifer. A unique finding was the reduction in predictive uncertainty along the groundwater flow path. This finding correlated well with the numerical model outputs which showed closer fits to the observation data near the end of the aquifer compared to those near the top of the aquifer where the tracer was injected.  Physical solute transport processes were identified and described as part of the modelling. These included the increase in dispersivity with travel distance and the spatial distribution of the aquifer hydraulic properties. Analytical modelling was a useful tool in identifying physical processes, aquifer characteristics and the variation in aquifer hydraulic properties both spatially and with depth.  An important finding was the value of undertaking multiple modelling approaches. This is because each approach has its own advantages and disadvantageous and by comparing the results of different approaches, the true facts about the aquifer system are made clearer.</p>

scholarly journals Influence of initial aperture field under varied in-situ stress conditions on incipient karst formation in carbonate rocks

2020 ◽  
Author(s):  
Xiaoguang Wang ◽  
Mohammed Aliouache ◽  
Qinghua Lei ◽  
Hervé Jourde
Keyword(s):  
Fractured Rocks ◽  
Reactive Transport ◽  
Flow Direction ◽  
Onset Time ◽  
Fracture Network ◽  
In Situ Stress ◽  
Stress Conditions ◽  
Natural Fracture ◽  
Stress Dependent

&lt;p&gt;We use numerical simulations to investigate the role of initial aperture heterogeneity under varied in-situ stress loadings in the early-time karstification in an anisotropic natural fracture network. We found that the importance of the stress-dependent initial aperture effect on karstification depends on the relative relationship between the flow direction and structural hierarchy/anisotropy of the fracture network. When the flow occurs in the direction of the dominant fracture set with more through-going discontinuities, karst conduits only develop locally along a few large fractures with a preferential orientation for frictional sliding under the differential stress due to enhanced transmissivity caused by the important shear-induced dilation. In contrast, when flow is in the direction transverse to the dominant fracture set, the far-field stress loading has a negligible impact on the emergent dissolution pattern while only somewhat impact on the onset time of breakthrough. In this case, the developed conduits are much more tortuous with numerous branches. In both cases, the presence of initial aperture variability enhances the stress effects and significantly changes the dissolution pattern and delays the breakthrough time. Our results demonstrate that the flow heterogeneity induced by geometrical complexities and in-situ stress conditions seems to play an essential role in the karstification processes in fractured rocks.&lt;/p&gt;&lt;p&gt;The proposed reactive transport model based on realistic fracture networks may be used to investigate the spatial relationship between tectonic structures and karst cavities. Our results demonstrate that the heterogeneity induced by geometrical complexities and in-situ stress conditions may play a decisive role in the karstification processes in fractured rocks. Thus, they must be properly considered in reactive transport simulations to make reliable designs for practical engineering applications.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords&lt;/strong&gt;: discrete fracture network, karst, network topology, reactive flow, in-situ stress&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document