Rock Mass Temperature Research Articles

Development of Best Practice Guideline for the management of hot holes in surface coal mines

Surface coal operations in which mining activities are conducted above old underground workings experience hot holes after drilling. In a coal mine, hot holes are defined as shot holes, which after being drilled have an in-hole ambient temperature of 40°C or above or show a temperature increase of 3°C or more during monitoring. Hot holes and other cavities, such as cracks, pose health and safety risks to workers, such as exposure to hot air and high concentrations of noxious gases released from these holes. In addition, workers may be exposed to premature detonation of explosives caused by in-hole temperature increases and chemical reactions. To this end, Coaltech Research Association commissioned a project to develop a Best Practice Guideline for the management of hot holes. This paper is a compilation of the activities conducted in the development of the Best Practice Guideline between 2021 and 2022. The activities included a review of standard operating procedures and hot-hole temperature-measuring and -monitoring devices, and the assessment of current hot-hole procedures at selected mines. The results indicated that management of hot holes requires a focus on pre-emptive risk assessment of mining blocks, identification of hot holes using the correct temperature-measuring devices, and continuous monitoring of hot holes from the time of drilling until just before blasting. Hot-hole management accessories, such as polyvinyl chloride sleeves, were found to be effective in insulating the hot-hole emulsion from the rock mass temperature, thus preventing the potential for premature detonation.

Study on mechanism of effect of flowing water and transferring heat on rock mass temperature in curved fracture

Domestically and internationally, the effect of fracture flowing water and transferring heat on the temperature field of surrounding rock in high-level radioactive waste repositories is a popular research area. Compared with straight fracture flowing water and transferring heat, there are few relevant literatures about the heat transfer of curved fracture water flow. Based on the conceptive model of flowing water and transferring heat in curved fractured rock mass, the influence of flowing water and transferring heat in “I”, “L”, , and shaped fractures on the temperature field of rock mass is calculated by using discrete element program. The findings indicate that: When the model goes into a stable state under four working conditions, the rock on the x = 0–2 m mostly forms a heat transfer path from left to right; the x = 2–4 m primarily forms a heat transfer path from bottom to top, and the temperature gradient reveals that the isotherm of 40–45 °C is highly similar to the shape of four different fractures, indicating that flowing water and transferring heat in the fracture configuration dominate the temperature field of the right side rock mass. The direction of the flowing water and transferring heat of the fracture exerts a dominant effect on the temperature of the rock mass than the length.

Study on number of geothermal wells based on flowing water and transferring heat in rock mass

The scientific selection of the number of pumping wells is directly related to the geothermal exploitation efficiency. In this paper, a new method is proposed to study the influence of different number of pumping wells on the geothermal exploitation efficiency. In order to study the influence mechanism of the number of pumping wells on the temperature of rock mass, based on the conceptual model of geothermal exploitation, 3DEC program was applied to analyze the evolution characteristics of rock mass temperature field and water temperature at the exit of pumping wells under a different number of pumping wells. With the number of pumping wells increasing from 1 to 6, the thermal stacking effect in the same direction of rock mass between the central pumping wells became increasingly strong, which led to the rising outlet water temperature of the pumping wells, the average temperature gradient of pumping wells gradually decreasing by 40.99% or so, and the heat conduction rate of water flow of pumping wells decelerating slowly. And the average temperature gradient of the rock reduced by approximately 47.4%, with the thermal conduction rate of the rock between pumping wells slumping little by little. The time for the model to reach a stable state is shortened.

Numerical study on surrounding rock mass temperature field of Kangding tunnel no. 2 considering wind flow

Numerical study on surrounding rock mass temperature field of Kangding tunnel no. 2 considering wind flow

Research on the thermo-hydraulic response characteristics of pore-fissure media using mixed finite volume method

After lengthy diagenesis and tectonic movement, a rock mass inevitably develops many pores and micro-fissures. A numerical simulation method was employed to study the thermal response characteristics of the rock mass under temperature seepage coupling by treating it as a pore-fissure medium and considering its anisotropic properties. Based on the mixed finite volume method (FVM), a numerical scheme of the governing equation for the temperature seepage coupling of the pore-fissure medium is derived, with the program solution module independently written in C++. On this basis, a numerical test model of the fissured mudstone is established to analyze the distribution of the rock mass temperature field under various thermal conductivities and the influence of fissure permeability on the seepage field. The mixed FVM results revealed that the temperature and water pressure distributions near the fissure were closely related to the directionality of thermal conductivity in the rock mass, as well as the thermal conductivity and permeability coefficient, respectively, of the fissure itself. Comparison with results from the finite element software ABAQUS demonstrated significant advantages of the proposed method when solving temperature and seepage problems in discontinuous geological bodies containing hiatuses, mutations, and fissures.

A new mathematical modeling approach for thermal exploration efficiency under different geothermal well layout conditions

The water temperature at the outlet of the production well is an important index for evaluating efficient geothermal exploration. The arrangement mode of injection wells and production wells directly affects the temperature distribution of the production wells. However, there is little information about the effect of different injection and production wells on the temperature field of production wells and rock mass, so it is critical to solve this problem. To study the influence mechanism of geothermal well arrangement mode on thermal exploration efficiency, the conceptual model of four geothermal wells is constructed by using discrete element software, and the influence law of different arrangement modes of four geothermal wells on rock mass temperature distribution is calculated and analyzed. The results indicated that the maximum water temperature at the outlet of the production well was 84.0 °C due to the thermal superposition effect of the rock mass between the adjacent injection wells and between the adjacent production wells. Inversely, the minimum water temperature at the outlet of the production well was 50.4 °C, which was determined by the convection heat transfer between the water flow and the rock between the interval injection wells and the interval production wells. When the position of the model injection well and production well was adjusted, the isothermal number line of rock mass was almost the same in value, but the direction of water flow and heat transfer was opposite. The study presented a novel mathematical modeling approach for calculating thermal exploration efficiency under various geothermal well layout conditions.

Recycling of drainage brines by means of re-injection in Udachny Mine

The permafrost zone in Levoberezhny 2 Site, represented by the Upper Cambrian carbonate–terrigenous rock strata up to 270 m thick, is studied. It is found that during injection, brines first flow along fractures and pores, and dissolve ice fill in them. The permafrost rocks degenerate as a result, and extra porosity is generated together with formation of a manmade aquifer. The analytical flow model of brine disposal in permafrost rocks in Udachny Mine represents the analytical flow model in dry soil, with rock permeability varied from zero to maximum values to describe frozen and thawed zones. The hydrogeological research of permeation by the numerical modeling method used GMS MODFLOW environment. The key complexity of the permeation problem consists in the fact that permeability coefficient and storage capacity of permafrost rocks greatly increase with time of injection. The highest degradation of ice takes place in the injection site; brines are displaced deeper in rock mass at the front velocity governed by density of joints, ice content, injection flow rate, mineralization of brines, temperature of rock mass and brines, etc. The permeation problem was solved using the method of alternation of quasi-stationary states in conformity with the modern hydrogeology and frost in the permafrost rock mass, and in accord with experience of drainage brine re-injection in Udachny Mine, subject to the key requirement of free flow of drainage brine into the permafrost rock zone at the eliminated discharge of water into local stream flows.

Environmental forcings and micro-seismic monitoring in a rock wall prone to fall during the 2018 Buran winter storm

This study reports a comparative analysis of the environmental conditions and micro-seismicity recorded on a rock wall resulting from an intense meteorological event. The findings are focused on a quarry wall located in the Acuto Field Laboratory (Central Italy), where multi-parametric environmental monitoring is operating and an Artificial intelligence Camera Prototype has been placed to detect rock falls reaching a railway target. Six accelerometers were installed to detect micro-seismic events caused by the expected strong thermal transient caused by the Buran storm on February 2018. Within a few hours, a steep decrease in the average air and rock mass temperature down to 8 °C was recorded, and −4 °C and −8 °C were reached for the rock and air temperatures, respectively. A total of 103 micro-seismic events were analysed with respect to both rainfall and thermal forcing: while no correlation with rainfall was reported, the steep thermal transient was responsible for the strain effect that occurred during the heating phase of the rock mass following the Buran storm. An elastic deformation event with a maximum daily amplitude of 165 μ strain was recorded by the strain gages installed on the mm-joints due to the rock heating and cooling caused by the variation in temperature. The collected evidences show the relevance of short thermal transients in modifying stress conditions within rock masses and their relationship to a peculiar micro-seismic response. The main outcomes established the key role played by integrated monitoring systems to better understand the relationship between vibrational behaviour and environmental forcings in terms of understanding the precursors to rock failure.

The influence of temperature on the detonation velocity of selected emulsion explosives

ABSTRACT Many years of research on more effective and safer explosives led to the development of emulsion explosives. They are the second most commonly used group of explosives in the world, primarily due to the fact that they are a good alternative to ANFO explosives or dynamites. Their key advantage in underground applications is the lower content of toxic fumes in the detonation products. Emulsions are also characterized by high detonation velocity, high water resistance, low value of critical diameter and mechanical loading capacity. Multiple factors related to the applied mining method influence the detonation parameters of emulsion explosives. One such parameter is the time between the loading of the explosive into the blast hole and firing, which in the case of underground copper mines in Poland can even last up to 48 hours. This becomes a particularly significant issue due to the increasing depth of mining in Polish copper mines and the high virgin temperature of rock mass at these depths. Experiences related to the use of explosives and their efficiency under such conditions confirm the intuitive thesis that high ambient temperature has a negative impact on the explosives’ effectiveness. In this regard, research concerning the influence of temperature on the detonation velocity of selected emulsion explosives was carried out, including bulk and packaged explosives. The tests were performed for different conditioning temperatures, which are all locally observed in Polish copper mines. The obtained results confirmed the significant influence of temperature on the velocity of detonation of the considered explosives.

Analysis of Coupled Three-Dimensional Seepage and Temperature Fields in Fracture Network of Rock Mass

The coupling effect of seepage and temperature fields in fractured rock mass is a hot topic in the area of water conservancy, nuclear waste disposal and geothermal resources development. A coupling mathematical model of the seepage, flow temperature and rock mass temperature fields in the fracture network of rock mass is established based on the seepage and temperature interaction. A calculation program is developed and applied to calculate the seepage and temperature fields of the dam foundation of a water conservancy project. The interaction mechanism of the seepage, flow temperature and rock mass temperature fields is analyzed in this paper. Results show that the seepage field largely influences the temperature field, which can provide several suggestions for the deep underground disposal of nuclear waste, geothermal resources development and fractured rock mass in dam foundations. Considering the coupling effect of the seepage, flow temperature and rock mass temperature fields by the fracture network method is necessary.

3D Remote survey of a rock wall hosting a multi-sensor monitoring system in a test-site (Acuto, Italy)

A multi-sensor monitoring system was installed in an abandoned quarry at Acuto (Frosinone - Central Italy) to test multi-sensing and multi-parametric remote techniques for early warning incase of rock failures threating strategic infrastructures. The multisensory monitoring system consist in: i) a meteo-climatic system, including a conventional weather stations and an innovative TSA-BOXone; ii) a geotechnical system, including thermometer for the rock mass temperature, strain-gauges for micro-fractures of rock mass, extensometers on open joints for detecting stress-strain conditions; iii) a nanoseismic monitoring system was also temporary installed to detect low magnitude vibrations to be regarded as precursors of rock failures. To correctly design the multi-parametric monitoring system, the rock wall was scanned to identify the main joint sets.Three GPS monographs were preliminary obtained in order to spatially geocoding the rock wall. From November 2015 to May 2016 remote scanning surveys were carried out on the quarry face by two different approaches: i) topographic 3D survey by Leica Total Station; ii) optical survey by 3D photos technique analyzed by Structure from Motion technique. The topographic survey provided high definition geocoded point clouds. These outputs were compared with the ones obtained by the SFM technique on 3D photos to test their reliability. At this aim, a Gaussian bi-modal distribution of the surveyed distances was obtained from each measurement; the comparison among the so derived distributions demonstrates that the computed errors are negligible and the main differences result at the boundaries of the sampled 3D domain. This comparison encourages the use of the photography technology by SfM technique to obtain multi-temporal geocoded point clouds for change detection analyses to point out evidences of scar zones due to slope failures. Thisapproach guarantees a very quick and accurate practice with easy management hardware and low software costs.

Unsteady temperature field of surrounding rock mass in high geothermal roadway during mechanical ventilation

To explore the spatial-temporal evolution law of rock mass temperature in high geothermal roadway during mechanical ventilation, a series of experiments were conducted based on the physical simulation test system of thermal and humid environment in high geothermal roadway, which is a method independently developed by China University of Mining and Technology. The results indicate that during ventilation, the disturbed region of the temperature extends gradually from shallow area to deep area in the surrounding rock mass of the roadway. Meanwhile, the temperature increases as the exponential function from shallow area to deep, with steady decrease of the temperature gradient and heat flux. As the ventilation proceeds, the relationship between dimensionless temperature and dimensionless time approximately meets Hill function.

Impact of rock mass temperature on potential power and electricity generation in the ORC installation

The basic source of information for determining the temperature distribution in the rock mass and thus the potential for thermal energy contained in geothermal water conversion to electricity, are: temperature measurements in stable geothermic conditions, temperature measurements in unstable conditions, measurements of maximum temperatures at the bottom of the well. Incorrect temperature estimation can lead to errors during thermodynamic parameters calculation and consequently economic viability of the project. The analysis was performed for the geothermal water temperature range of 86–100°C, for dry working fluid R245fa. As a result of the calculations, the data indicate an increase in geothermal power as the geothermal water temperature increases. At 86°C, the potential power is 817.48 kW, increases to 912.20 kW at 88°C and consequently to 1 493.34 kW at 100°C. These results are not surprising, but show a scale of error in assessing the potential that can result improper interpretation of the rock mass and geothermal waters temperature.

Temperature field analysis in salty rocks at shaft mouth under operation of a freezing system

The 3D mathematical model of temperature conditions in salty rock mass at shaft mouth takes into account parameters and modes of freezing unit operation, temperature of ambient air and air in the shaft, as well as nonuniformity and rate of salinity of enclosing rocks. The model allows dynamics of temperature variation in rocks around the shaft and load-bearing capacity of each pole of head frame foundation depending on rock mass temperature and salinity. Different variants of freezing unit operation are considered to select the variants to ensure the required load-bearing capacity of the head frame poles and the diamond shaft lining safety.

THM (Thermo-hydro-mechanical) coupled mathematical model of fractured media and numerical simulation of a 3D enhanced geothermal system at 573 K and buried depth 6000–7000 M

Hot dry rock geothermal energy is almost inexhaustible green energy. However, it makes slow progress in practice due to slow theory development. In this study, a three dimension thermo-hydro-mechanical coupled model of fractured media was established to simulate the extraction of HDR (Hot dry rock) geothermal energy based on the geological characteristics (geothermal gradient of 50 K/km, buried depth of 6250–6750 m) of Tengchong geothermal field in China. The simulation results show the variation in both field of temperature, stress, seepage and fracture aperture during heat extraction. The temperature in fracture face increased exponentially from injection well towards production well while extracting heat. The initial rock mass temperature of 573 K decreases to 423 K after 9-year running. The initial water pressure gradient in the fracture reached 0.17 MPa/m near the injection well and then decreased to 0.052 MPa/m after 1 year. The fracture aperture was triple of the initial value and the permeability coefficient increased by nine times over the 9-year operation period. That seepage resistance of artificial storage reservoir gradually decreased could improve extracting geothermal energy more efficiently. The amount of extracted heat declined exponentially with running time. The total extracted geothermal energy over 9 years was 5977 MWa and rock mass temperature decreased to 423 K.

암반공동 열에너지저장과 지상식 열에너지저장의 열손실 비교 분석

A large-scale high-temperature thermal energy storage(TES) was numerically modeled and the heat loss through storage tank walls was analyzed using a commercial code, FLAC3D. The operations of rock cavern type and above-ground type thermal energy storages with identical operating condition were simulated for a period of five consecutive years, in which it was assumed that the dominant heat transfer mechanism would be conduction in massive rock for the former and convection in the atmosphere for the latter. The variation of storage temperature resulting from periodic charging and discharging of thermal energy was considered in each simulation, and the effect of insulation thickness on the characteristics of heat loss was also examined. A comparison of the simulation results of different storage models presented that the heat loss rate of above-ground type TES was maintained constant over the operation period, while that of rock cavern type TES decreased rapidly in the early operation stage and tended to converge towards a certain value. The decrease in heat loss rate of rock cavern type TES can be attributed to the reduction in heat flux through storage tank walls followed by increase in surrounding rock mass temperature. The amount of cumulative heat loss from rock cavern type TES over a period of five-year operation was 72.7% of that from above-ground type TES. The heat loss rate of rock cavern type obtained in long-period operation showed less sensitive variations to insulation thickness than that of above-ground type TES.

Primary Rock Temperature Fields in Czech and Polish Part of the Upper of the Upper Silesian Coal Basin / Pole temperatury pierwotnej skał w czeskiej i polskiej części górnośląskiego okręgu węglowego

Knowledge of the temperature of rock mass is no doubt of substantial meaning, both for the solution of economicaly demanding protection of mine workers in difficult microclimatic environment and for perspective usage of geothermal energy from the depth of the earth. International cooperation of our and Polish specialists is in this sense more than welcome, also because the exploitation of coal seams takes place in the same Upper Silesia rock coal basin. This profesional article is concentrated on complex analysis of temperature fields of the Ostrava- Karviná district, mainly from results of thermologging measurements in geological survey boreholes both on surface and underground, and also from the actual temperature measurements in the coal mines. One chapter of this article describes the original approach to the survey of temperature field and its prognosis in the Polish part of the Upper Silesia coal basin by a researcher from GIG Katowice. The most suitable method of analysis of primary temperature field seemed the preparation of isocurves of temperature(isothermal lines) for the existing mine working areas, even if the method of obtaining them was different. The Czech method is based on determination of the quantitative dependence of temperature on the rock mass depth from the abovementioned measurement results, calculation of geothermal gradients and the following recalculation of real temperature values for various depth levels. Then isothermal lines for these depth levels are created together with colour distingushing of their value limits. The Polish method is sufficiently described in a dedicated chapter. The conclusion of the article underlines the decisive role of the structuraly tectonic composition of the rock mass on the temperature field in the long term thermic evolution of the Earth.

Study of the effect of medium flow parameters on heat transfer in the laboratory coaxial model of a borehole heat exchanger

Borehole heat exchangers (BHE) are more and more commonly applied for recovering energy from rock mass renewable sources and for rational heat managing in the heating/ cooling installations. BHE exploitation simulations can be either provided by mathematic methods, included in examples [8, 9] or by carrying out tests at laboratory stands. BHEs located in the Laboratory of Geoenergetics in Faculty of Drilling, Oil and Gas AGH University of Science and Technology are being used to conduct research in area of presented interests [1]. A research on the efficiency of heat transfer in a coaxial borehole heat exchanger is described in this paper. In recent times theme of adapting old or not used anymore oil and gas wells is highly increased. The most important fact is that every deep well that is being transferred into BHE has to be of centric construction. This is for minimizing of pressure [7]. The objective of the study is to adjust the materials and the configuration of a vertical borehole heat exchanger in such a way that the heat transfer processes can be analyzed. A series of experimental measurements were performed for various capacities. Three various pipe materials were used in the experiments: polyethylene (PE), polyvinylchloride (PVC), polypropylene (PP) or a combination there of. The vertical borehole heat exchanger operated at the rock mass temperature. In laboratory conditions the rock mass heat source was substituted with 4 heating blankets, 80 W each. The polyethylene and polyvinylchloride pipes constituted flow channels in two zones. Their diameter differed depending on the applied combinations. The inner diameter of the heat exchanger equaled to 25.3 mm. The

Automatic and continuous measurements of temperature in mining headings

The problem of the actual rock mass temperature poses considerable difficulties in practical mining engineering. So far, measurements have been made with the use of thermistor thermometers. These do not provide infallible data on temperature, particular as concerns a certain distance from a rib into the rock mass, and they do not allow continuous data logging. Accordingly, a device has been designed and made for measuring the rock mass temperature, together with a thermal probe. Experiments and tests carried out with this device indicate that it complies with the requirements relating to the needs of underground mining.

Multiple Artificial Geothermal Cracks in a Hot Dry Rock Mass for Extraction of Heat

Theoretical analysis is made for multiple geothermal cracks. A periodic array of two-dimensional cracks is considered as a model of the multiple geothermal cracks, and is anlayzed on the basis of the two-dimensional theory of quasi-static thermo-elasticity. The singular integral equations are derived from the boundary conditions, and they are solved by applying the combination of inversion formula and collocation method. Numerical results for the fluid temperature at an outlet, the rock mass temperature, the shape of the geothermal cracks and the stress distribution around the geothermal cracks are shown in graphs.