Numerical modeling of groundwater flow, solute ...

Numerical modeling of groundwater flow, solute transport and heat transfer in porous geological media Daniela Blessent, PhD

Profesora Ingeniería Ambiental Universidad de Medellín

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Contents • Geological porous media in hydrogeology • Conceptual models

• Applications • Solute transport in heterogeneous media • Hydraulic interference tests • Infiltration in waste rock piles • Coupled surface-subsurface water modeling • Heat transfer in geological media

• Conclusion 2

Introduction • Representative Elementary Volume (REV)

V1

V2

V3

Adaptado de Bear (1972) y http://echo2.epfl.ch/VICAIRE/mod_3/chapt_1/main.htm

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Introduction • Porosity

PRIMARY POROSITY

SECONDARY POROSITY 4

Introduction • Equivalent Porous Medium (EPM) • Double/dual porosity • Double/dual permeability

For heterogeneous media

• Stochastic facies EPM 5

Equivalent Porous Medium (EPM) • It is the simplest model • It has been the first one to be used to model groundwater flow and transport in fractured geological media (Bodin et al., 2003) • It is viable is a REV can be defined

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Equivalent Porous Medium (EPM) • It can be applied to fractured geological media if: • Fracture density is high • Fracture orientation is random • Fracture aperture is almost constant • Large scale modeling is conducted

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Double/Dual Continuum • Two media with different properties are considered

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Solute transport: double porosity model • Water is not flowing in the matrix • Double-porosity transport in mobile and immobile regions

Immobile region Only mass Transport by diffusion

Mobile region flujo

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Solute transport: double permeability model • Water is flowing in the matrix

Matrix Low permeability flow

Fractures or second medium High permeability flow 10

Double porosity vs. double permeability model • Water is flowing in the matrix

(Clifford, 2001)

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• Conclusion 12

Solute Transport

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Field-scale predictive capabilities • DFMD, DP (dual porosity), and EPM conceptual models for transport in fractured porous medium are compared by simulating vertical transport of pesticide compound through a 16m-thick saturated fractured clayey till near Havdrup in Denmark

Objective: to build robust calibrated models to predict contamination migrations for future scenarios

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Simulation domain

Till Units Sand, local aquifer

Aquitard

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Solute Transport • Solute exchange between the mobile and immobile regions is simulated by introducing the following relation in addition to transport in a 3D porous medium

 imm cimm  t

 imm  0

imm   imm  c  cimm 

First-order mass transfer coefficient between the mobile and immobile regions

 imm

3imm Dimm  2 B

where Dimm is the diffusion coefficient of the immobile region [LT-2] and B the fracture half-spacing [L] 16

Equivalent hydraulic conductivity • Estimation of the Keq for EPM and DP conceptual models, for a set of parallel fractures of half-aperture b, half-spacing L, and hydraulic conductivity Kf bK f   L  b  K m  K eq  L

(Bear, 1993)

• The fracture porosity, which is also the mobile porosity θm in a DP model, is evaluated with the following relation: b1 b2 nf   L1 L2

(Bear, 1993)

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Equivalent dispersivity • When the EPM model is applied, an equivalent dispersivity incorporates the effects of both the porous matrix and the discrete (Kool and Wu, 1991)

• The determination of the effective dispersivities is one of the most critical steps in the application of the EPM approach • Non realistic values may be calculated 18

Numerical results

Simulations conducted with FRAC3Dvs (Therrien and Sudicky 1996)

• Contaminant concentration at the domain bottom boundary

Concentration is evaluated here

Base case scenario

New recharge rate

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Numerical results

Simulations conducted with FRAC3Dvs (Therrien and Sudicky 1996)

• Numerical results with solute degradation: EPM works better than DP model

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• Conclusion 21

Hydraulic interference tests

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Hydraulic interference tests

Objective: estimating hydraulic rock properties, which are required to properly build underground nuclear waste disposal facilities 23

Site location: Finland

http://nordic.businessinsider.com/finlands-100000-year-tombs-for-storing-nuclear-waste-is-drawing-the-worlds-admiration-2017-1/

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Hydraulic interference tests • Pumping and observation wells

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Hydraulic interference tests • Definition of EPM “facies” based on fracture density:

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Hydraulic interference tests • Geostatistical realization de rock facies

Realizations conducted with software T-PROGS

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Hydraulic interference tests • Result: estimation of hydraulic conductivity

Prior Information

95% confidence Intervals for the estimated facies hydraulic conductivities

Simulations conducted with HydroGeoSphere Coupled with PEST

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• Conclusion 29

Waste rock piles

http://woodsperson.blogspot.com.co/2012/02/potential-impact-of-waste-rockand.html

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Waste rock piles • Waste rock is the material with low metal contents (cannot be economically recoverable) • Waste rock is usually stored in large, partially water-saturated, porous heaps or piles • Sulfides are present in waste rock, AMD can be produced by these piles due to sulfide oxidation

https://www.dwa.gov.za/Projects/AMDFSLTS/default.aspx

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Waste rock piles • Acid mine drainage (AMD)

http://www.peterscreek.org/PetersCreekWatershed/p cwaAMD1.html

http://www.accdpa.org/conservation-solution-center/watershed/abandoned-mine-drainage/

http://www.youngreporters.org/menu/award s/photos/2013/yre-2nd-place-acid-minedrainage-at-ribeira-guas-fortes

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Waste rock piles • Waste rock is usually stored in large, partially water-saturated, porous heaps or piles Conceptual representation of the internal structure of a WRP constructed in benches on a flat surface by pushdumping (adapted from Aubertin et al., 2005)

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Waste rock piles • Preferential pathways can be associated with macropores and lens of high permeability material • This behaviour has been observed in • Laboratory tests • Field tests

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Waste rock piles • Modeling of preferential pathways in waste rock piles Objective: reducing infiltration into the piles and thus AMD

(Lefebvre et al., 2001) 35

Waste rock piles • Modeling of preferential pathways in waste rock piles • Variable-saturated water flow • Water retention curves have to be determined

(PEREGOEDOVA, 2012)

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Waste rock piles • EPM and stochastic EPM facies in a 7 m high waste rock pile Compacted fine grained material in the Top and bottom layer Waste rock in the middle

3 waste rock materials: stochastic facies realizations 37

Waste rock piles • Simulated saturation After 65 days

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Waste rock piles • Contrast in degree of saturation within short distances is a critical issue for waste rock piles, as these parameters control the hydrogeological, geochemical and geotechnical responses

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Waste rock piles • Vertical degree of saturation profile

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• Conclusion 41

Coupled surface-subsurface water flow

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Coupled surfacesubsurface water flow

Scheme of surface and subsurface coupling (modified from Liggett et al. 2012)

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Coupled surface-subsurface water flow • Modeling scenarios with different ainfall temporal distribution, mesh resolution, coupling length, physical processes (subsurface flow, surface flow, and evapotranspiration), and soil heterogeneity

Objective: analyzing the sensitivity of simulated pore-water pressure and infiltration

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Coupled surface-subsurface water flow • Rainfall temporal distribution and model domain

EPM vs. Stochastic EPM facies to represent Hydraulic properties of rock blocks (CASE D) 45

Coupled surface-subsurface water flow • Impact of conceptual model on simulated water pore-pressure

Stochastic EPM facies

EPM 46

Coupled surface-subsurface water flow • Impact of evapotranspiration on simulated water pore-pressure

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• Applications • Solute transport in heterogeneous media • Hydraulic interference tests • Infiltration in waste rock piles • Heat transfer in geological media

• Conclusion 48

UNESCO IGCP636 project

https://www.unescoigcp636.org/

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UNESCO IGCP636 project

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Heat transfer modeling • Get started with heat transfer modeling • OpenGeoSys, HydroGeoSphere, Comsol Multyphysics, Feflow Objective: comparing different modeling tools

• Large scale numerical modeling • Nevado del Ruiz geothermal reservoir Objective: geothermal potential estimation

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Heat transfer modeling • Get started with heat transfer modeling Temperature gradient °K/m

T q  L

Layer 1: λ=3.6 W/m·K Layer 2: λ=2.8 W/m·K

Layer 3: λ=1.2 W/m·K Heat flow W/m2 Thermal conductivity W/m·K

Layer 4: λ=4.5 W/m·K 52

Heat transfer modeling • Large scale numerical modeling • Nevado del Ruiz geothermal reservoir Trabajo de grado de Vélez (2015)

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Heat transfer modeling • Large scale numerical modeling • Nevado del Ruiz geothermal reservoir

Trabajo de grado de Córdoba (2017)

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Heat transfer modeling • This model takes in account an heterogeneous thermal conductivity in the “Pes” layer • Decreasing of thermal conductivity with increase in temperature • Nevado del Ruiz geothermal reservoir

Trabajo de grado de Córdoba (2017)

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Heat transfer modeling

Simulations conducted with OpenGeoSys http://www.opengeosys.org/

(Vélez et al. submitted)

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Heat transfer modeling • Inferring terrestrial heat flow from thermal response test data combined with a temperature profile (Vélez et al., 2017)

Objective: assessing the terrestrial heat flow

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Heat transfer modeling • Simulated and observed temperature along the borehole (Vélez et al., 2017)

Simulations conducted with Comsol MultyPhysics (heat transfer and optimization modules) 58

Conclusions • There are several different applications of hydrogeological modeling to porous media • EPM is the first approach to be considered for modeling purposes • Field and laboratory work is mandatory to properly characterize the geological media and to reduce the uncertainty associated with the simulation results 59

Event

September 22 Universidad de Medellín 8 am – 12 pm FREE ASSISTANCE

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Gracias Contacto: Daniela Blessent: dblessent@udem.edu.co

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