Hydrothermal Model Research Articles

Gold and sulfur sources of the Taipingdong Carlin-type gold deposit: Constraints from simultaneous determination of sulfur isotopes and trace elements in pyrite using nanoscale secondary ion mass spectroscopy

The Youjiang basin in southwestern China is known for the occurrence of abundant Carlin-type gold deposits similar to those of northern Nevada in the U.S. Among them, Taipingdong is a representative deposit nearby the super-large Shuiyindong Mine in the Huijiabao ore field. Though some data of in-situ sulfur isotopes and trace element geochemistry of pyrite have been collected recently, the ore-forming fluid source and genesis model of the deposits remain under debate. The mineral chemistry and isotopic compositions of Au-carrying pyrite in the Taipingdong gold deposit were studied in detail using nanoscale secondary ion mass spectroscopy (NanoSIMS) in this study to further understand the aforementioned issues. Petrographic observations identified two types of pyrite: syn-sedimentary framboidal pyrites and hydrothermal pyrites. Back-scattered electron observations and electron microprobe analysis elemental mapping showed that the latter have three generations, termed as As-poor Py1 (the core), As-rich Py2 (the middle overgrowth), and As-weak Py3 (the outmost overgrowth zone), respectively. NanoSIMS high-resolution multiple elemental maps showed the following: 1) Py1 is poor in As and other trace elements; Py2 is rich in As and Cu and relatively rich in Se; and Py3 is rich in Au and relatively rich in As, Cu, and Se. 2) Gold is heterogeneously distributed as solid solution and nanoparticle, focusing on the outermost rim of the zoned pyrite (Py3). Other metal nanoparticles of Cu, Se, and Pb were identified in Py2 or Py3. 3) Arsenic elemental mapping showed dense mineral growth of pyrite in the subzones. 4) Line profile analyses of trace elements showed high Cu contents in Py2 and Py3 and that As is positively correlated with Cu but not with Au.In-situ sulfur isotopic analyses showed that the δ34S values range from −15.4‰ to 6.1‰ with a median of 2.0‰ for Py1, from −1.8‰ to 7.1‰ with a median of 1.4‰ for Py2, and from −3.0‰ to 6.2‰ with a median of 3.9‰ for Py3. Intensive spot analyses showed a slight fluctuation in S isotopic values within a short distance in pyrite subzones. The δ34S values of Py2 and Py3 dropped into a narrow range from −3‰ to 6‰ with a median of 3.3‰. Considering the composition and isotopic characteristics, Py1 is classified as pre-ore pyrite and Py2 and Py3 as ore pyrites with Py3 representing the Au climax event. The Au state and distribution in the pyrite of the Taipingdong deposit imply that the ore-forming fluid was unsaturated for Au, but occasionally hosted metal nanoparticles. The Au climax event occurred towards the end of the fluid evolution. The decoupling of As and Au in the ore pyrites indicate that the Au-carrying capacity of the pyrite was limited by the higher concentration of Cu ions in the ore-forming fluids.The S isotopic data of the Taipingdong deposit is similar to the available in-situ S isotopic range of −5‰ to 5‰ of the representative Au deposits in the basin except for the Lannigou (Zhenfeng) Mine. The S isotopic deviation of pyrite in the Huijiabao ore field to the typical magmatic fluid (±0‰) may be the result of a mixture of hydrothermal and basin fluid to a certain extent. This feature combined with the intensive fluctuation of trace elements and isotopic compositions over a short duration accord with the characteristics of magmatic hydrothermal fluid. Combined with the strong silicification characteristic of the host rock and the previous geophysical works in the ore district, a magmatic hydrothermal model might be suitable for the Taipingdong gold deposit and even other Carlin-type gold deposits in the Youjiang basin.

Development and application of a simulation approach for fire and structure interaction of concrete members subject to spalling

SummaryThis paper describes the development and illustrates the use of an approach to model the mechanical performance of a concrete bridge and its structural components exposed to fire and subject to spalling. The work is motivated by some recent fire incidents that involved concrete bridges, the poor state of an increasing number of bridges throughout the United States (which makes them more vulnerable to fire damage), and the lack of design codes and standards that adequately protect bridges against fire. An important objective of the work is to develop a method to predict spalling that captures the principal physical and chemical phenomena but is simple enough so that it can be implemented in a 3‐D structural simulation. The first step in the approach involves using a hydrothermal model to determine if and at what temperature spalling occurs for a specified concrete mix (defined by its composition, type of aggregate, water‐cement ratio, porosity, permeability, etc), free moisture content, and heating rate. The second step uses the resulting “critical spalling temperature” in a coupled thermal and mechanical analysis to determine how spalling affects the performance of the concrete member. The approach is illustrated for two standard fire resistance tests conducted on posttensioned concrete slab systems reported in the literature. The paper concludes with a list of recommendations for additional work to improve the predictive capability of the heat and mass transfer and structural models and to address several challenges with the implementation of the spalling criteria in the structural model.

Large-scale urban underground hydro-thermal modelling – A case study of the Royal Borough of Kensington and Chelsea, London

The shallow subsurface of dense cities is increasingly exploited for various purposes due to the significant rise in urban populations. Past research has shown that underground activities have a significant impact on local subsurface temperatures. However, the resulting spatial variability of ground temperature elevations on a city-scale is not well understood due to the lack of sufficient information and modelling complexity at such large scales. Resilient and sustainable planning of underground developments and geothermal exploitation in the short and long-term necessitate more detailed, more reliable knowledge of subsurface thermal status. This paper investigates the impact of some common underground heat sources such as train tunnels and residential basements on subsurface temperature elevation on a large scale and highlights the influence of local geology, hydrogeology, density, and type and arrangement of the heat sources on ground thermal disturbance. To tackle the size issues and computational expenses of such a large-scale problem, a semi-3D hydro-thermal numerical approach is presented to capture the combined influence of underground built environment characteristics coupled with ground properties on ground temperature elevation within the Royals Borough of Kensington and Chelsea (RBKC), London. Numerical results show that the extent of ground thermal disturbance is mostly affected by geological and hydrogeological characteristics in permeable ground (River Terrace Deposits). Density and spatial distribution of heat sources, however, are critical parameters in ground temperature evaluation in highly impermeable ground such as London Clay Formation. The locality of temperature rise and potential ground energy within immediate impermeable ground surrounding heat sources versus significantly large extent of ground thermal disturbance in permeable ground, highlights the significant dependency of ground thermal state and geothermal potential at the studied site to the ground and underground built environment characteristics and necessitates a better understanding of shallow subsurface thermal state for a sustainable and resilient urban underground development.

Numerical study on heat extraction performance of multistage fracturing Enhanced Geothermal System

A conceptual Enhanced Geothermal System (EGS) with triplet horizontal well layout is proposed, in which the injection well is flanked by two production wells. The injection well is completed with perforated casing, followed by multistage fracturing with casing packers. Two production wells are drilled through the stimulation zone induced by multistage fracturing and completed openhole to maximize contact with the reservoir. Based on a fully coupled hydrothermal (HT) model accounting for local thermal non-equilibrium (LTNE), sensitivity analysis and optimization for EGS design parameters are conducted. Simulation results show that increasing circulation rate only facilitates the heat extraction rate before thermal breakthrough, but cannot improve the heat extraction performance at the end of EGS operation. Compared with the fracture aperture, the increase in the stimulation zone permeability is more conducive to reducing the injection pressure and increasing the cumulative output thermal power. Insufficient or excessive fracturing stages are detrimental to economic heat extraction. It is found that more uniform flow into each perforation can achieve better thermal sweep efficiency and prevent local thermal breakthrough. The stimulation zone has an optimal reservoir permeability to match the fracture aperture. The optimum number of fracturing segments for a specified wellbore length is obtained. The preferable zone for the production well is between the fracture front and the outermost periphery of the stimulation zone.

Boundary condition control on inter-aquifer flow in the subsurface of Berlin (Germany) – new insights from 3-D numerical modelling

Abstract. We investigate the degree of hydraulic interconnection between the different (regional to local) groundwater compartments with respect to the choice of boundary conditions and their impact onto the groundwater safety beneath the urban centre of Berlin, capital city of Germany. To this end, we carry out a systematic study based on 3-D hydrothermal models differing in terms of imposed parametric set-ups of the hydrogeology, as well as different surface forcing with respect to their impact on fresh groundwater production. The study area is part of the Northeast German Basin and consists of a thick sequence (up to 5 km) of differently consolidated sedimentary deposits. This sedimentary succession features a sequence of alternating aquifers (reservoirs) and aquitards which are connected to different degrees, each one depicting a specific composition of its mineralised pore water. The uppermost aquifer system (made up mainly of poorly consolidated siliciclastic rocks) acts as the main freshwater reservoir used for groundwater production by the municipal water supplier. This compartment is incompletely sealed from the brackish to saline aquifers extending at greater depths by a regional clay-enriched aquitard, the Oligocene Rupelian Clay. The latter shows a heterogeneous thickness distribution due to erosion during the latest glacial periods resulting in local discontinuities. This aspect opens to the potential risk of contamination of the drinking water reservoir from mixing with the saline groundwater upconing, locally enhanced by shallow pumping activities. Based on our results and their correlation with available isotopic and chemical analysis of water samples, we demonstrate how hydraulic connection between the different compartments is indeed likely to occur thus supporting the possibility of a contaminant rise from the saline aquifers below through either natural or anthropogenic (pumping) forcing.

Quantifying perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) seed germination responses to water potential and temperature with a hydrothermal time model

ABSTRACT In New Zealand, a commonly sown pasture combination is perennial ryegrass with white clover. The hydrothermal time model (HTT) was used to quantify germination under different temperature (T) and water potential (WP) conditions for white clover ‘Nomad’ and perennial ryegrass ‘Stellar AR1’. Seeds were germinated in vitro under a range of T × WP combinations, and HTT models were fitted to germination time course data. Rapid germination of white clover under optimum T and WP was reflected by a much lower value for its HTT constant compared with perennial ryegrass (10.8 vs 80.7 MPa °C d). However, the lower base water potential for perennial ryegrass (−1.29 vs −0.495 MPa) and a higher threshold temperature for thermoinhibition (21.8 vs 18.3°C), meant that predicted perennial ryegrass germination was more resilient in warm dry conditions. HTT models can be used to assist decisions about the timing of perennial ryegrass and white clover sowing.

Influences of copper columns on thermal hydraulic performance of the vapor chamber

A simplified and efficient hydrothermal model was adapted and validated with both the experiment and literature data to further investigate the mechanism and influence of different columns on thermal performance of the vapor chamber (VC). The experiment was conducted by testing a T-shaped VC under different heat loads, and the maximum error with the numerical model was about 2 K. Factors including column dimension, column number and column structures were analyzed. Results show that sintered wick ring layer could provide auxiliary liquid circulation paths, reduce the pressure drop in the fluid circulation, and provide additional heat conductive passages. The column dimension shows enhancement on heat transfer capability of VC as the area ratio in the range of 0~0.5, with a maximum decrease by about 6.45% of the thermal resistance compared with the void VC. By comparing with other column structures, copper columns with sintered wick rings were found to the optimal type for enhancing the thermal performance of VC.

The use of impulse and stepped‐frequency radar to characterize the hydric behaviour of a porous pavement structure

ABSTRACTThis study focusses on examining the behaviour of an innovative asphalt pavement which is created as a solar energy collector, using non‐destructive testing involving ground‐penetrating radar. The concept of heat exchanger is based on the use of drainage asphalt in the bonding layer through which a heated fluid flows via gravity to de‐ice the roadway. In order to develop hydrothermal models for a test site representing such a pavement, the saturated porous layer assumption was required when the water level in each tank (up‐ and downstream of the structure) was same as the top of the porous layer. Two ground‐penetrating radar techniques were tested at this test site: a ground‐coupled impulse radar and an air‐coupled stepped‐frequency radar. The impulse ground‐penetrating radar, a high‐efficiency non‐destructive testing technique which is widely used in civil engineering, provides accurate geometric information, especially for pavement investigation. In the second innovative approach, air‐coupled stepped‐frequency radar was combined with full‐waveform inversion to obtain quantitative information, while retrieving the electromagnetic properties of the successive pavement layers.We concentrated on the early‐stage water imbibition in the pavement structure using the impulse ground‐penetrating radar to estimate the fluid transfer velocity and both ground‐penetrating radar techniques to verify the saturated porous layer assumption in the steady state. Ground‐coupled radar enabled us to follow the water front and to capture different water‐transfer behaviours in the porous asphalt layer. Our observation could be explained by the vertical topology of the upper watertight interface. Air‐coupled stepped‐frequency ground‐penetrating radar presented similar results to ground‐coupled ground‐penetrating radar but provided a quantitative estimate of the changes within the porous layer during the test.

Effects of Excavation Damaged Zone on Thermal Analysis of Multi-layer Geological Repository

As the present single-layer repository concept requires too large an area for the site of the repository, a multi-layer repository concept has been suggested to improve the disposal density. The effects of the excavation damaged zone around the multi-layer repository constructed in the deep host rock on the temperature distribution in the repository were analyzed. For the thermal analysis of the multi-layer repository, the hydrothermal model was used to consider the resaturation process occurring in the buffer, backfill and rock. The existence of an excavation damaged zone has a significant effect on the temperature distribution in the repository, and the maximum peak temperatures of double-layer and triple-layer repositories can rise to 7℃ and 12℃, respectively depending on the size of the excavation damaged zone and the degree of decrease of the thermal conductivity. The dominant factor affecting the peak temperature in the multi-layer repository is the decrease of thermal conductivity in the excavation damaged zone, and the excavation damaged zone formed around the deposition hole has more significant effects on the peak temperature than does the excavation damaged zone formed around the disposal tunnel.

Analytical solutions of fractal-hydro-thermal model for two-phase flow in thermal stimulation enhanced coalbed methane recovery

Thermal stimulation is a useful supplementary mining technique for the enhancement of coalbed methane recovery. This technique couples the temperature change with gas-water two-phase flow in the mining process. Many integer dimension hydro-thermal models have been proposed but cannot well describe this coupling because two-phase flow and heat conduction are usually non-linear, tortuous and fractal. In this study, a fractal-hydro-thermal coupling model is proposed to describe the coupling between heat conduction and two-phase flow behaviors in terms of fractional time and space derivatives. This model is analytically solved through the fractal travelling-wave method for pore pressure and production rate of gas and water. The analytical solutions are compared with the in-situ coalbed methane production rate. Results show that our proposed fractal-hydro-thermal model can describe both heat and mass transfers in thermal stimulation enhanced coalbed methane recovery.

FDEM‐TH3D: A three‐dimensional coupled hydrothermal model for fractured rock

SummaryThis paper proposes a three‐dimensional coupled hydrothermal model for fractured rock based on the finite‐discrete element method to simulate fluid flow and heat transport. The 3D coupled hydrothermal model is composed of three main parts: a heat conduction model for the rock matrix, a heat transfer model for the fluid in the fractures (including heat conduction and heat convection), and a heat exchange model between the rock matrix and the fluid in the fractures. Four examples with analytical solutions are provided to verify the model. A heat exchange experiment of circulating water in a cylindrical granite sample with one fracture is simulated. The simulation results agree well with the experimental results. The effects of the fracture aperture, fluid viscosity, and pressure difference on the heat exchange between the fluid and rock are studied. Finally, an application concerned with heat transport and fluid flow in fractured rock is presented. The simulation results indicate that the 3D fully coupled hydrothermal model can capture the fluid flow and temperature evolution of rocks and fluids.

Experimental validation of 2D hydrothermal modelling of porous pavement for heating and solar energy retrieving applications

Hydraulic snow melting system using pavement structure has been employed for some critical roads in order to prevent ice and snow formation. This paper describes a 2D hydrothermal numerical model of a hydraulic system that circulates a fluid through a bonding porous asphalt layer. A set of boundary conditions have been defined, and a model of heat and mass transfer has been developed. This model can predict temperature field in pavement structure and surface conditions when the fluid circulates in the porous bonding layer. Model development is described and validated in this paper using data collected from the full-scale hydraulic system.

Comment on the papers by Hovland et al. (2018) “Large salt accumulations as a consequence of hydrothermal processes associated with 'Wilson cycles': A review” (part 1 and 2)

Abstract The geological model of large hydrothermal salt accumulations linked to Wilson cycles as reviewed by Hovland and Coworkers, un-adequately addressed: (1) the lack of well exposed submarine volcanogenic hydrothermal feeder zone, (2) the sequential precipitation of different hydrothermal evaporite minerals and (3) the absence of hydrothermal alteration mineralogy around the major evaporites. These aforementioned points are the main classical features to be linked to the hydrothermal model of evaporites. Experimentally, heating seawater during submarine volcanism firstly results in precipitation of anhydrite followed by halite, other evaporite minerals, serpentine, brucite, talc, metallic sulfides-oxides and related hydrothermal alterations. In this regard, Mg/Ca – Cl, Mg/Ca – SO4, Mg/Ca – Na/Cl and Mg/Ca - TDS biplots show that hydrothermal brines of riftogenic and subduction zone settings plot in a separate field than the subduction-related Andean Salars as well as seawater. This indicates that the hydrothermal serpentinization of basaltic oceanic crust and mantle peridotites removes magnesium from seawater and incorporates the Mg into serpentine, brucite and other hydrous Mg-silicates rather than the hydrothermal brines. Finally, our comment arose from a recent global classification of the most distinguished marine, non-marine and exhalative hydrothermal evaporites.

The Muruntau Deposit: Geodynamic Position and a Variant of Genetic Model of the Ore-Forming System

The paper presents the results of original structural studies conducted over a long time within the Kyzylkum ore province and at the Muruntau deposit (Central Asia), including the period when the central part of the deposit, as well as horizons at the eastern and southeastern flanks (abandoned or inaccessible at present), were available to visit. Owing to the geodynamic and structural analysis of the region and the deposit itself, several stages of deformation that created the Muruntau interference structure have been identified. These stages were attributed to the Caledonian (subduction, collision, and transpression regimes), Hercynian (subduction, collision, and transpression regimes), and Cimmerian (transpression regime) cycles of tectonogenesis. The fault–fracture structures of these stages are accompanied by the development of various newly formed (vein–veinlet-metasomatic) mineral assemblages. Based on the averaged characteristics of gold mineralization in various mineral formations, a morphogenetic classification of orebodies was developed and their role in the deposit was revealed. The morphological features of the Main Muruntau ore deposit are considered. A critical review of the results of isochron age dating was made. The subduction–hydrothermal model of the formation of the giant Muruntau gold ore deposit is discussed.

Combining a dynamic simulation tool and a multi-criteria decision aiding algorithm for improving existing District Heating

The work aims to evaluate the recovering potential of excess heat in the return pipe of a district heating (DH) for heating some substations.The proposed method combines a DH simulation tool and a multi-criteria decision aiding algorithm. It is based on the analysis of the measured return temperatures at each sub-station in order to identify those with high potential of efficiency gains by using the return flow (with support of the supply pipe when needed). Combinations of substations from this set of eligible ones define potential scenarios of connection to the return pipe. The impacts of each scenario on the DH operational performance and the energy savings are evaluated with a detailed hydro-thermal model. The technical parameters and the energy efficiency are not the only points of view in the selection process “of best compromise” scenarios for the improvement of the DH, so that we propose a complex decision aiding process, involving multiple criteria, dealing with different points of view (economic, energy, technical…) and different decision makers. The evaluations of the scenarios on the criteria are summed up in a so-called performance table and aggregated by an outranking model (MR-Sort) to identify relevant scenarios.This methodology is illustrated by the example of a part of the DH in Nantes (France). Interpretation of data from substations of a specific branch showed the potential of connecting some of them to the return pipe. Six scenarios were generated and evaluated with four criteria. Then, the Multi-criteria Decision Aiding method associated to two actors who have different priorities lead to not obvious results at a first glance.

Influence of a Vertical Shift in the Current Velocity during Propagation of Contaminated Water from an Underwater Outfall under Stratified Conditions

The features of the spatial structure of coastal water caused by the impact of a nonstationary deep source of waste under stratified conditions is studied using a numerical hydrothermal model. The task is solved for the case of contaminated water outfall in Golubaya Bay of the city of Sevastopol. It is found that the activity of the source is accompanied by a jet and a stream of contaminated water. The pycnocline layer is mostly polluted with the contaminated area reaching 0.3–0.5 km2. The increase in the vertical shift of the velocity of background current leads to the increase in the existing period of contaminated zones and displacement of the stream of waste water toward the free surface (the stream becomes more localized vertically). The fields of contamination, temperature, and salinity of water have a complex spatial structure.

Hydrothermal Germination Models: Assessment of the Wet‐Thermal Approximation of Potential Field Response

Hydrothermal (HT) models can be used to characterize seed germination response to field‐variable conditions of temperature (T) and water potential (Ψ). Hydrothermal response data are relatively difficult to generate, which limits their utility for large‐scale comparisons of inter‐ and intraspecies germination response. Previous studies have hypothesized that HT germination response can be estimated using a simple model for thermal‐time accumulation above a fixed threshold of environmental Ψ (wet‐thermal [WT] model). The purpose of this study was to test this hypothesis by explicitly comparing HT and WT germination rates and estimated cumulative germination response of 13 rangeland grass seedlots under simulated conditions of field‐variable T and Ψ. We used a 44‐yr weather record to parameterize a seedbed‐microclimate model for estimation of hourly T and Ψ at seeding depth for a sandy loam soil type at the Orchard field test site in southwestern Ada County, Idaho. Hydrothermal and WT germination responses for each hour of the simulation were estimated for 13 range grass seedlots. We found that overestimation of germination rate by thermal accumulation at low Ψ contributed relatively little to WT model error rates, and that >95% of the variability in predicted germination response could be explained by WT germination response above a Ψ threshold of −0.3 to −0.5 MPa. Given the pulse‐like nature of favorable germination conditions in the field, this modeling approach may have immediate and wide potential application, as there are a relatively large number of thermal‐germination datasets currently available for rangeland plant species.

Hydrothermal model for small-scale linear Fresnel absorbers with non-uniform stepwise solar distribution

The study of the hydrothermal behaviour of water-steam is a key topic in direct steam generation through solar concentrators. The hydrothermal behaviour is affected by the non-uniformity in the solar flux distribution along the axis of the linear absorber. The non-uniformity produces non-illuminated regions at the absorber ends (especially in small Linear Fresnel Collector prototypes or in non-rectangular configurations of Fresnel systems), and partially illuminated regions due to the gradual contribution of the mirror rows to the reflected solar radiation in the absorber. The aim of this paper is to present a new general hydrothermal model for linear absorbers that accounts for this non-uniformity and allows simulating Linear Fresnel systems of any size, mirror field geometry, and working conditions. The present model considers both, one phase flow—for heating/cooling of the liquid or the superheated steam—and two-phase flow—for describing boiling or condensation mechanisms—using a homogeneous mix model. The model was validated against experimental data from prototypes under different working conditions. Infrared thermography was used to measure the absorber temperature profile. A good agreement between experimental and predicted datasets was found, which confirmed the reliability of the model.

Spatial and temporal variations of thaw layer thickness and its controlling factors identified using time-lapse electrical resistivity tomography and hydro-thermal modeling

Quantitative understanding of controls on thaw layer thickness (TLT) dynamics in the Arctic peninsula is essential for predictive understanding of permafrost degradation feedbacks to global warming and hydrobiochemical processes. This study jointly interprets electrical resistivity tomography (ERT) measurements and hydro-thermal numerical simulation results to assess spatiotemporal variations of TLT and to determine its controlling factors in Barrow, Alaska. Time-lapse ERT measurements along a 35-m transect were autonomously collected from 2013 to 2015 and inverted to obtain soil electrical resistivity. Based on several probe-based TLT measurements and co-located soil electrical resistivity, we estimated the electrical resistivity thresholds associated with the boundary between the thaw layer and permafrost using a grid search optimization algorithm. Then, we used the obtained thresholds to derive the TLT from all soil electrical resistivity images. The spatiotemporal analysis of the ERT-derived TLT shows that the TLT at high-centered polygons (HCPs) is smaller than that at low-centered polygons (LCPs), and that both thawing and freezing occur earlier at the HCPs compared to the LCPs. In order to provide a physical explanation for dynamics in the thaw layer, we performed 1-D hydro-thermal simulations using the community land model (CLM). Simulation results showed that air temperature and precipitation jointly govern the temporal variations of TLT, while the topsoil organic content (SOC) and polygon morphology are responsible for its spatial variations. When the topsoil SOC and its thickness increase, TLT decreases. Meanwhile, at LCPs, a thicker snow layer and saturated soil contribute to a thicker TLT and extend the time needed for TLT to freeze and thaw. This research highlights the importance of combination of measurements and numerical modeling to improve our understanding spatiotemporal variations and key controls of TLT in cold regions.

A 2D coupled hydro-thermal model for the combined finite-discrete element method

Based on the combined finite-discrete element method (FDEM), a two-dimensional coupled hydro-thermal model is proposed. This model can simulate fluid flow and heat transfer in rock masses with arbitrary complex fracture networks. The model consists of three parts: a heat conduction model of the rock matrix, a heat-transfer model of the fluid in the fracture (including the heat conduction and convection of fluid), and a heat exchange model between the fluid and rock at the fracture surface. Three examples with analytical solutions are given to verify the correctness of the coupled model. Finally, the coupled model is applied to hydro-thermal coupling simulations of a rock mass with a fracture network. The temperature field evolution, the effect of thermal conductivity of the rock matrix thermal conductivity and the fracture aperture on the outlet temperature are studied. The coupled model presented in this paper will enable the application of FDEM to study rock rupture driven by the effect of hydro-thermo-mechanical coupling in geomaterials such as in geothermal systems, petroleum engineering, environmental engineering and nuclear waste geological storage.