Personne : Therrien, René
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Université Laval. Département de géologie et de génie géologique
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Voici les éléments 1 - 10 sur 15
- PublicationAccès libreNumerical simulations of shallow groundwater flow and heat transport in a continuous permafrost setting under the impact of climate warming(Conseil national de recherches du Canada, 2018-06-11) Shojae Ghias, Masoumeh; Therrien, René; Lemieux, Jean-Michel; Molson, John W. H.Numerical simulations of coupled groundwater flow and heat transport are used to address how hydrogeological conditions can affect permafrost dynamics. The simulations are based on a 2D vertical-plane conceptual model of a study site at the Iqaluit Airport, Nunavut, Canada, which includes a 50 m deep permafrost terrain with a shallow active layer, overlain by a paved taxiway with winter snow-covered embankments. Coupled groundwater flow and advective-conductive heat transport with freeze-thaw dynamics, temperature-dependent porewater freezing functions and latent heat are included in the model. The simulation results show that a smooth (low-slope) freezing function with a higher residual unfrozen moisture content produced a deeper thaw front compared to that using a steeper freezing function, generating a maximum increase in the depth to permafrost of 17.5 m after 268 years. Permafrost thaw rates in high-permeability zones within a heterogeneous system were also relatively higher compared to an otherwise equivalent homogeneous soil, resulting in a maximum increase of 2.6 m in the depth to permafrost after 238 years. As recharge water cools while flowing along the upgradient permafrost table, advectively driven heat transport is paradoxically shown to temporarily increase the height of the permafrost table in downgradient areas.
- PublicationAccès libreNumerical evaluation of grouting scenarios for reducing water inflows in underground excavations – Goldcorp’s Éléonore mine study case(2017-10-02) Blessent, Daniela; Therrien, René; Grenon, Martin; Lemieux, Jean-Michel; Lajoie, Pierre-Luc; Domingue, Catherine; Molson, John W. H.Water inflows through fracture networks are one of the many challenges that the Éléonore mine has to face. Although pregrouting of pilot holes during mine development has been proven to efficiently reduce water inflows into mine excavations, the actual design methods are empirical and can be optimized to increase grouting efficiency and decrease the associated costs. Optimization of the amount of cement needed for pre-grouting is achieved by designing the grouting approach based on the location of major faults around the excavations. Here, a base case finite-element numerical model and associated sensitivity analyses are used to simulate groundwater inflows into a stope, based on the Éléonore mining site characteristics. Simulations are conducted for testing various grout injection scenarios for various major fault locations around the stope. Sensitivity analyses have shown that for a fault located above the stope, the inflow reduction is greater when the zone between the fault and the stope is grouted instead of directly grouting the fault itself. Also, in the case of a fault intersecting a stope, the results have demonstrated that the fault itself should be grouted as widely as possible, instead of sealing only the immediate surroundings of the stope.
- PublicationAccès libreNumerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well(American Geophysical Union, 2015-07-20) Nowamooz, Ali; Therrien, René; Lemieux, Jean-Michel; Molson, John W. H.Methane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with a multiphase flow and multicomponent numerical model. The conceptual model used for the simulations assumes that the target shale formation is 200 m thick, overlain by a 750 m thick caprock, which is in turn overlain by a 50 m thick surficial sand aquifer, the 1000 m geological sequence being intersected by a fully penetrating borehole. This succession of geological units is representative of the region targeted for shale gas exploration in the St. Lawrence Lowlands (Québec, Canada). The simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer. The leakage of fluids can subsequently lead to the contamination of groundwater resources and/or, in the case of methane migration to ground surface, to an increase in greenhouse gas emissions. The minimum reported surface casing vent flow (measured at ground level) for shale gas wells in Quebec (0.01 m3/d) is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration. The simulations suggest that an adequately cemented borehole (with a casing annulus permeability kc math formula 1 mD) can prevent methane and brine leakage over a time scale of up to 100 years. However, a poorly cemented borehole (kc math formula 10 mD) could yield methane leakage rates at the base of an aquifer ranging from 0.04 m3/d to more than 100 m3/d, depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation. These values are compatible with surface casing vent flows reported for shale gas wells in the St. Lawrence Lowlands (Quebec, Canada). The simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years, depending on cementation quality and hydrodynamic properties of the casing annulus. Simulated long-term brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10−5 m3/d (10 mL/d) to 10−3 m3/d (1 L/d). Based on scoping calculations with a well-mixed aquifer model, these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration in a pristine aquifer to 1 mg/L, which is significantly below the commonly recommended aesthetic objective of 250 mg/L for chloride.
- PublicationRestreintRapid groundwater recharge dynamics determined from hydrogeochemical and isotope data in a small permafrost watershed near Umiujaq (Nunavik, Canada)(Springer, 2020-01-25) Cochand, Marion; Barth, Johannes (Johannes A. C.); Therrien, René; Geldern, Robert van; Lemieux, Jean-Michel; Fortier, Richard; Molson, John W. H.Hydrogeochemical data are used to better understand recharge dynamics and to support a hydrogeological conceptual model in a 2-km2 watershed in a discontinuous permafrost zone in Nunavik, Canada. The watershed contains an upper (surficial) and lower aquifer within Quaternary deposits, above and below a marine silt layer containing ice-rich permafrost mounds. The analysis is based on water samples from precipitation, groundwater monitoring wells, ground ice in permafrost mounds, thermokarst lakes and a perennial stream. Groundwater geochemistry in both aquifers reflects young, poorly evolved waters, with mainly Ca-HCO3 water types and low mineralisation ranging from 11 to 158 mg/L total dissolved solids (TDS), implying short pathways and rapid travel times of a year or less. While relatively low, TDS signatures in groundwater and surface water show increasing values downgradient. Groundwater isotope values (δ18OH2O and δ2HH2O) are often strongly influenced by snowmelt, while those of thermokarst lakes show evidence of evaporation. Recharge along the cuesta contributes to a transverse component of groundwater flow within the valley with higher TDS and δ13CDIC values influenced by open-system weathering. Even where permafrost-free, the marine silt unit has a strong confining effect and plays a more important role on recharge dynamics than the discontinuous permafrost. Nevertheless, the vulnerability of these types of hydrogeological aquifer systems is expected to increase due to rapid recharge dynamics associated with the gradual loss of the confining effect of permafrost. This hydrogeochemical data set will be useful as a baseline to document impacts of permafrost degradation on the hydrogeological system.
- PublicationAccès libreNumerical evaluation of grouting scenarios for reducing water inflows from major faults in underground excavations(Springer, 2019-01-19) Blessent, Daniela; Therrien, René; Grenon, Martin; Lemieux, Jean-Michel; Lajoie, Pierre-Luc; Domingue, Catherine; Molson, John W. H.Water inflows through fracture networks are a major economic and safety issue in underground mines. Although pre-grouting of pilot holes during mine development efficiently reduces water inflows into mine excavations, current design methods remain empirical. We used a finite-element numerical model to simulate groundwater inflow into a stope with the objective of finding the best configuration to increase pre-grouting efficiency for sealing faults while decreasing the associated costs. We designed simulations to test various grout injection scenarios for two different major fault locations around the stope, based on the site characteristics of the Éléonore mine (Québec, Canada). Sensitivity analyses show that, for a fault located above the stope, grouting the zone between the fault and the stope reduces inflow more than directly grouting the fault. Also, in the case of a fault intersecting a stope, the simulations suggest that the fault itself should be grouted as widely as possible, instead of sealing only the immediate surroundings of the stope.
- PublicationRestreintSemi-automated filtering of data outliers to improve spatial analysis of piezometric data(Verlag Heinz Heise, 2015-04-19) Therrien, Pierre; Tremblay, Yohann; Comeau, Guillaume; Therrien, René; Talbot Poulin, Marie-Catherine; Lemieux, Jean-Michel; Fortier, Richard; Molson, John W. H.The identification and removal of data outliers remains a major challenge for spatial analysis of piezometric data. In this context, a simple semi-automated procedure for filtering outliers of depth to static water level was developed and used as a part of a regional groundwater-mapping project in the Québec Metropolitan Community, Québec, Canada. Following a few basic steps of data control, potential outliers were detected using two simple automated steps: (1) identifying water levels that are deeper than the 99th percentile of a high-reliability dataset compiled by groundwater professionals and assumed to adequately represent depths to static water level, and (2) using moving averages within a search radius of 250 m calculated around each well. All detected potential outliers were visually examined in a geographic information system and compared to neighbouring data before being kept or discarded. To evaluate the efficiency of the procedure, exploratory statistics, histograms and semi-variograms of the initial, intermediate and filtered datasets were compared to the high-reliability dataset. Objective interpolation was then performed using ordinary kriging. A cross-validation analysis showed a less biased and more accurate interpolation after applying the proposed outlier filtering procedure. Qualitative knowledge of the hydrogeological settings is an important component of this procedure which combines advantages of both manual and automated processing, making the procedure adaptive and easy to use. The final outcome of the proposed procedure is an improved interpolation map of depth to static water level along with minimised and low squared estimation errors.
- PublicationRestreintControls on permafrost thaw in a coupled groundwater flow and heat transport system : Iqaluit Airport, Nunavut, Canada(Springer, 2016-12-22) Shojae Ghias, Masoumeh; Therrien, René; Lemieux, Jean-Michel; Molson, John W. H.Numerical simulations of groundwater flow and heat transport are used to provide insight into the interaction between shallow groundwater flow and thermal dynamics related to permafrost thaw and thaw settlement at the Iqaluit Airport taxiway, Nunavut, Canada. A conceptual model is first developed for the site and a corresponding two-dimensional numerical model is calibrated to the observed ground temperatures. Future climate-warming impacts on the thermal regime and flow system are then simulated based on climate scenarios proposed by the Intergovernmental Panel on Climate Change (IPCC). Under climate warming, surface snow cover is identified as the leading factor affecting permafrost degradation, including its role in increasing the sensitivity of permafrost degradation to changes in various hydrogeological factors. In this case, advective heat transport plays a relatively minor, but non-negligible, role compared to conductive heat transport, due to the significant extent of low-permeability soil close to surface. Conductive heat transport, which is strongly affected by the surface snow layer, controls the release of unfrozen water and the depth of the active layer as well as the magnitude of thaw settlement and frost heave. Under the warmest climate-warming scenario with an average annual temperature increase of 3.23 °C for the period of 2011–2100, the simulations suggest that the maximum depth of the active layer will increase from 2 m in 2012 to 8.8 m in 2100 and, over the same time period, thaw settlement along the airport taxiway will increase from 0.11 m to at least 0.17 m.
- PublicationAccès libreTopical collection : hydrogeology of a cold-region watershed near Umiujaq (Nunavik, Canada)(Verlag Heinz Heise, 2020-03-06) Ouellet, Michel; Therrien, René; Lemieux, Jean-Michel; Fortier, Richard; Molson, John W. H.A cold-region watershed located in the discontinuous permafrost zone near Umiujaq (Nunavik, Canada) was studied in order to increase understanding of the subarctic water cycle and permafrost dynamics. This essay gives an overview of the research, summarised in a collection of six papers that: respectively characterize the physical three-dimensional cryo-hydrogeological system, present a detailed water balance of the watershed, characterize groundwater and surface-water hydrogeochemistry, describe the application of a tracer method to determine groundwater fluxes, develop a two-dimensional numerical model identifying impacts of groundwater flow on permafrost dynamics, and present a parameter sensitivity analysis. The work serves as a guide for developing site characterization plans at similar permafrost-impacted sites and for evaluating their groundwater resource potential.
- PublicationRestreintIntegrated hydrological modeling of climate change impacts in a snow-influenced catchment(Water Well Journal Pub. Co., 2018-11-19) Therrien, René; Lemieux, Jean-Michel; Cochand, FabienThe potential impact of climate change on water resources has been intensively studied for different regions and climates across the world. In regions where winter processes such as snowfall and melting play a significant role, anticipated changes in temperature might significantly affect hydrological systems. To address this impact, modifications have been made to the fully integrated surface-subsurface flow model HydroGeoSphere (HGS) to allow the simulation of snow accumulation and melting. The modified HGS model was used to assess the potential impact of climate change on surface and subsurface flow in the Saint-Charles River catchment, Quebec (Canada) for the period 2070 to 2100. The model was first developed and calibrated to reproduce observed streamflow and hydraulic heads for current climate conditions. The calibrated model was then used with three different climate scenarios to simulate surface flow and groundwater dynamics for the 2070 to 2100 period. Winter stream discharges are predicted to increase by about 80, 120, and 150% for the three scenarios due to warmer winters, leading to more liquid precipitation and more snowmelt. Conversely, the summer stream discharges are predicted to fall by about 10, 15, and 20% due to an increase in evapotranspiration. However, the annual mean stream discharge should remain stable (±0.1 m3/s). The predicted increase in hydraulic heads in winter may reach 15 m and the maximum decrease in summer may reach 3 m. Simulations show that winter processes play a key role in the seasonal modifications anticipated for surface and subsurface flow dynamics.
- PublicationRestreintCoupled cryo-hydrogeological modelling of permafrost dynamics near Umiujaq (Nunavik, Canada)(Springer, 2020-02-12) Therrien, René; Lemieux, Jean-Michel; Dagenais, Sophie; Fortier, Richard; Molson, John W. H.A two-dimensional (2D) cryo-hydrogeological numerical model of groundwater flow, coupled with advective-conductive heat transport with phase change, has been developed to study permafrost dynamics around an ice-rich permafrost mound in the Tasiapik Valley near Umiujaq, Nunavik (Québec), Canada. Permafrost is degrading in this valley due to climate warming observed in Nunavik over the last two decades. Ground temperatures measured along thermistor cables in the permafrost mound show that permafrost thaw is occurring both at the permafrost table and base, and that heat fluxes at the permafrost base are up to ten times higher than the expected geothermal heat flux. Based on a vertical cross-section extracted from a 3D geological model of the valley, the numerical model was first calibrated using observed temperatures and heat fluxes. Comparing simulations with and without groundwater flow, advective heat transport due to groundwater flow in the subpermafrost aquifer is shown to play a critical role in permafrost dynamics and can explain the high apparent heat flux at the permafrost base. Advective heat transport leads to warmer subsurface temperatures in the recharge area, while the cooled groundwater arriving in the downgradient discharge zone maintains cooler temperatures than those resulting from thermal conduction alone. Predictive simulations incorporating a regional climate-change scenario suggest the active layer thickness will increase over the coming decades by about 12 cm/year, while the depth to the permafrost base will decrease by about 80 cm/year. Permafrost within the valley is predicted to completely thaw by around 2040.