Seepage Heat Research Articles

Modeling Study of Enhanced Coal Seam Gas Extraction via N2 Injection Under Thermal-Hydraulic-Mechanical Interactions.

N2 injection into coal seams can effectively enhance the gas flow capacity in the late stage of pumping, thereby improving the recovery rate and recovery efficiency of low coalbed methane (CBM). To reveal the thermodynamic flow coupling relationship between the reservoir and the gas phase and its transportation mechanism in the process of thermal N2 injection, a mathematical coupling model of N2 injection that considers the deformation of the coal seam, fluid transportation, and temperature change was established. The influence of the seepage heat transfer effect of the coal seam under the effect of N2 injection on the CH4 extraction rate was investigated using this model. Results indicate that the action mechanism of N2 injection in coal seams includes increasing seepage, promoting flow, and displacing gases. A higher initial coal seam temperature results in a smaller thermal expansion and deformation of the coal skeleton during thermal N2 injection and less pronounced coal permeability increase. A larger initial coal seam permeability results in more favorable N2 diffusion, which strengthens the flow-promoting effect on CH4. The effect of gas injection pressure on CH4 recovery is greater than that of the gas injection temperature: High pressure promotes N2 seepage, carries CH4 flow, and increases the CH4 diffusion effect, whereas higher temperature promotes the desorption of adsorbed gas in the coal seam and improves the recovery rate.

Heat Transfer Analysis of Enhanced Geothermal System Based on Heat-Fluid-Structure Coupling Model

Dry hot rock geothermal resources by virtue of its wide distribution, large reserves, clean and low-carbon, stable, high utilization rate, and other characteristics have been widely used. The enhanced geothermal system (EGS) is the most efficient approach for harnessing and exploiting geothermal energy from hot, arid rock formations. To investigate the impact of varying parameters on heat recovery in EGS operations, we employed the COMSOL numerical simulation software to construct a seepage heat transfer model for fractured rock masses. Essential parameters and boundary conditions were established, followed by conducting numerical simulations. Through the numerical simulation results, the temporal and spatial changes of coupling effects among seepage field, stress field, and temperature field in fractured rock mass were analyzed. We investigated the impact of water injection temperature, injection-production pressure difference, injection flow rate, and initial reservoir temperature on the heat transfer process. The findings indicate that raising the water injection temperature and injection-production pressure difference can enhance the reservoir’s heat recovery capability. However, it may also accelerate thermal breakthrough and reduce the system’s operational lifespan. The higher injection flow rate can improve the heat recovery efficiency. However, too large injection flow can cause problems in other aspects of the reservoir; increasing reservoir temperature leads to higher production temperatures, which can potentially result in dynamic catastrophes. Therefore, while ensuring the heat recovery efficiency of the system, the operation life of the system can be extended by adjusting the water injection temperature in stages, setting a reasonable injection and production pressure difference, and selecting an appropriate injection flow rate, so as to achieve the purpose of EGS optimization.

Monitoring heat transfer for seepage in earth-rock dams with clay cores considering damaged areas: Laboratory experiments and numerical modeling

This study conducted a laboratory test and two-dimensional numerical simulation on seepage heat monitoring of a core rockfill dam. A fully automatic laboratory test system for dam seepage monitoring has been developed, which can achieve automatic control of water flow and temperature, as well as automatic data collection. A flow-heat coupling model based on [Johansen, O., (1975). Thermal conductivity of soils. P. D. thesis. University of Trondheim, Norway, Trondheim] empirical thermal conductivity model was established through secondary development using COMSOL Multiphysics finite element software, and its accuracy was verified. The influence of the location of damaged leakage in the core wall of the dam on flow and heat migration was analyzed. Among the investigated conditions, a damaged channel with a curved cross-section causes the formation of the prominent arc in the saturation line of the dam body downstream, induces the largest increase in the average seepage discharge, and makes the dam body most unstable. The effects of damage on the temperature and seepage fields are positively correlated for different damage types. The presence of a damaged area induces sudden changes in the pressure, velocity, and temperature at each monitoring point. The pressure, velocity and temperature are correlated, and there is a lag in temperature transfer. This study provides a reference for the application of distributed fiber optic temperature measurement technology in core rockfill dam engineering, especially in terms of fiber optic placement position. The established numerical model can provide an accurate and effective reference method for identifying abnormal temperature data and locating dam leakage. Our next step will be to study the flow and heat transfer characteristics throughout the entire process from undamaged to dam failure.

Experimental research on the thermal conductivity of unsaturated rocks in geothermal engineering

The thermal conductivity of rock is an essential thermophysical parameter in geothermal engineering. Experiments have shown that when rock changes from an unsaturated to a saturated state, thermal conductivity can be increased by 50% at most. In this paper, the variation of thermal conductivity with saturation of 101 samples of six different rock types from Songliao Basin, Gonghe Basin, and Ordos Basin in China was measured in the laboratory. Correlations between saturation, porosity, internal structural characteristics of rocks and thermal conductivity were investigated. The results show that the effect of saturation on the thermal conductivity of rock increases exponentially with porosity. Based on three classical models and the relationship between porosity, saturation, and thermal conductivity, improved models and a fitted model of thermal conductivity are proposed. By comparing the improved models to the fitted model, the applicable scope of each model is obtained. The errors of each model are analyzed in detail. The average MAE value of the improved models is 0.405 and the average RMSE value is 1.207 over the applicable model scopes. The R2 of the fitted model is 0.94. Compared with experimental data from literature, MAE values of the improved models and the fitted model are 0.040 and 0.003 respectively. Unsaturated rock with a single fracture heat transfer model is established by simulation. A thermal-Hydrological coupling model is used to simulate seepage heat transfer through fracture. The effect of variable thermal conductivity simulation is the best with the experimental value, and the MAPE value was 8.3%. This study fills a gap in available models of unsaturated thermal conductivity of rock, and provide theoretical support for the accurate calculation of heat transfer efficiencies in related geothermal engineering applications.

Study on the intrinsic mechanisms underlying enhanced geothermal system (EGS) heat transfer performance differences in multi-wells

The effectiveness of the multi-well arrangement mode in enhanced geothermal systems in large-scale fields has been well established. However, the mechanisms that lead to variations in heat transfer performance between different numbers of well arrangements have remained unclear. In this study, the multi-well pattern was segmented into several double-well units and a mathematical model was constructed to investigate seepage heat transfer in enhanced geothermal systems using numerical simulation techniques. The lifespan and heat transfer characteristics of both multi-well and corresponding double-well units were examined, with supplementary experimental validation. Additionally, a flow reduction coefficient for multi-well systems was proposed to explain the differences in heat transfer performance caused by the pressure superposition of multiple-well seepage fields. It was found that heat extraction from a multi-well enhanced geothermal system is equivalent to the linear superposition of corresponding double-well units. Furthermore, the lifespan of multi-well systems is significantly longer than that of corresponding double-well systems due to the influence of the multi-well flow reduction coefficient. In fact, this difference can exceed threefold in nine-well arrangements, resulting in reduced efficiency of multi-well heat exchange. This work provides a novel perspective on exploring the intrinsic mechanisms that underlie differences in heat transfer performance in enhanced geothermal systems from a flow field perspective. It contributes to a better understanding of optimal well arrangement modes for enhanced geothermal systems and supports the development of large-scale geothermal fields.

Performance study on the seepage and heat transfer in a bench-scale multi-well infiltration intake system for seawater source heat pump

The Beach Well Infiltration Intake (BWII) system is one of the various methods for pumping seawater for Seawater Source Heat Pump (SWHP) systems that improve the stability, reliability, and energy efficiency of the SWHP systems in cold climate areas. Because of the limitations of the site conditions, it is difficult to perform experimental studies on the BWII system under different experimental conditions, especially for multi-well systems. Therefore, a BWII experimental system that incorporated nine beach wells was established in a laboratory in this paper. The goal was to study the seepage and heat transfer performance of the multi-well infiltration intake system and calculate the influencing range for pumping groundwater on sands in a sandbox. Then, an established seepage and heat transfer model of the BWII system was validated by the experiment. Based on the validated model, the method for designing an experimental sandbox was studied. The research results showed that the effective width increased with an increase in the distance between the pumping well and the long water tank. However, the effective width in the back part of the pumping well decreased with an increase in this distance. The result that the effective length decreased with an increase in this distance was contrary to our subjective expectations. When the distance between the pumping well and the long water tank was 0.5 m, the effective length and effective width were 1.5 ∼ 2.1 m and 0.9 m respectively. The formulas of the effective width and the effective length were derived. The experimental study provided a method to study the seepage and heat transfer performance of the BWII system and was complementary to the theoretical research and the practical engineering field research. The research results provided in this study will contribute to the establishment of a set of seepage heat transfer similarity test methods.

Heat tracing of embankment dam leakage: Laboratory experiments and 2D numerical modelling

Recently, the use of heat as a tracer to evaluate the process of leakage in embankment dams has attracted wide attention. A more accurate flow-heat coupling model of embankment dams could help us to better understand the patterns of water flow and heat transfer in embankment dams and provide a scientific basis for the seepage prevention and repair of these dams. In this paper, combined with thermal conductivity empirical models (TCEMs), the saturated-unsaturated flow-heat coupling model of embankment dams was established. Through laboratory sand tank experiments of concentrated leakage in embankment dams, the accuracy of the flow-heat coupling model under 10 types of TCEMs were tested and compared. The results show that the performance of the flow-heat coupling model varies under different types of TCEMs, and the Chung and Horton (1987) model shows better simulation effects, with a coefficient of determination (R2), root mean square error (RMSE) and relative error (Re) ranging from 0.916 to 0.980, 0.266–0.467℃ and 1.370–2.442%, respectively. Therefore, this model could better reflect the dynamic temperature variations in embankment dams. Finally, the flow-heat coupling model was improved by modifying the COMSOL built-in equation, i.e. built-in COMSOL model was replaced by the Chung and Horton (1987) model, which further improved the accuracy of the flow-heat coupling model in the numerical simulation of seepage heat monitoring. Based on the improved model, the concentrated leakage of embankment dams under dynamic water levels was simulated numerically. Under the condition of a dynamic water level, the flow velocity and pressure at the leakage passage are positively correlated with the water level change, and the temperature field also shows the same change trend.

Seepage and Heat Transfer Characteristics of Gas Leakage under the Condition of CAES Air Reservoir Cracking

The contradiction between supply and demand of energy leads to more and more attention on the large-scale energy storage technology; Compressed Air Energy Storage (CAES) technology is a new energy storage technology that is widely concerned in the world. The research of coupled heat transfer and seepage in fractured surrounding rocks is the necessary basis to evaluate the operation safety and effectiveness of CAES. Current studies point to the possibility of cracking in concrete liner seals, but the thermodynamic processes and leakage characteristics of compressed air in the presence of cracking and the heat transfer characteristics of seepage have not been addressed and reported. In order to investigate the leakage, the gas seepage and heat transfer law in fractured rock when the hard rock CAES gas reservoir seal cracks, the COMSOL fracture Darcy module, and the non-Darcy Forchheimer model are used as the constitutive seepage. The global ODE is used to calculate the thermodynamic process of compressed air in gas storage with coupled seepage and heat transfer process. The pressure and temperature of compressed air are obtained as the unsteady boundary of the seepage heat transfer model. A program for calculating the seepage and heat transfer characteristics of fractured surrounding rock in the CAES gas reservoir is established. On this basis, with the proposed Suichang CAES cavern as the background, the seepage and heat transfer characteristics of the fractured surrounding rock of the gas storage are studied. The results showed that when there are fewer cracks in the lining and surrounding rock of the air reservoir, the air pressure decreases due to a small amount of air leakage after 30 operation cycles, and the leakage rate of each cycle is 0.7% of the gas storage capacity, but it still meets the engineering requirements. If the plant is operating under these conditions, the charging rate will need to be increased by 1.2 kg/s per cycle charging stage. In the discharging and power generation phase, the high-pressure air that previously percolated into the rock mass cracks could flow back into the air storage through the lining cracks. Therefore, it is incorrect and unreliable to consider the gas which flows out from the inner surface of the lining as unusable. When the lining crack width is less than 0.3 mm, the seepage flow is Darcy flow and the non-Darcy effect can be ignored; when the lining crack width is greater than 0.5 mm, the non-Darcy effect of seepage cannot be ignored. The gas velocity in the surrounding rock fracture medium is on the order of 0.01 m/s with an influence range of over 100 m, and the gas velocity in the pore medium is on the order of 10-6 m/s with an influence range of 50 m. The findings of this study contribute to a better understanding of the interaction between the thermodynamic properties of compressed air and the seepage heat transfer process in compressed air storage underground reservoirs, as well as the gas leakage process in the event of liner seal cracking.

Influence of low temperature tail water reinjection on seepage and heat transfer of carbonate reservoirs

Seepage and heat transfer in the carbonate reservoir under low-temperature tail water reinjection is a complex coupling process, which is an important basis for scientific and reasonable evaluation of geothermal resource sustainability. This study based on the tracer test of double-well reinjection for carbonate heat reservoir, a coupling model of seepage field and temperature field of fracture network is established by using the finite element software COMSOL. The uncertainty analysis is carried out to study the fluid-thermal coupling process of carbonate fracture under the condition of low-temperature tail water reinjection.The variation law of seepage field and temperature field of thermal reservoir under low-temperature geothermal tail water reinjection is revealed, The variation of measured temperature of thermal reservoir pumping side under different reinjection conditions is predicted. The results show that the dominant fracture channels between wells of the fractured heat reservoir in Xian county geothermal field play an important role in controlling the seepage heat transfer. Under the coupling action of the seepage field, pressure field and the temperature field of the heat reservoir, the low-temperature tail water reinjection forms a preferential flow along the dominant channels, which is one of the important factors to consider in the prediction of thermal breakthrough. Reinjection pressure, temperature and well spacing are the main factors for artificial control of geothermal production and reinjection system. In the pumping and reinjection system of Xian county geothermal field, under the conditions of 0.5 MPa reinjection pressure, 30 °C reinjection tail water temperature and 270 m spacing between pumping and reinjection wells, the heat reservoir temperature at the pumping side decreased by 1.5 °C in 100 years.

An experimental study on monitoring the phreatic line of an embankment dam based on temperature detection by OFDR

In this study, temperature detection with distributed fibers was used to obtain data for a laboratory model of seepage heat in an embankment dam, and the temperature was monitored using optical frequency domain reflection (OFDR) technology with high temporal and spatial accuracies. First, the temperature field in the infiltrated region of the dam body during the seepage test showed changes similar to that measured by OFDR temperature-sensing fibers. Then the heat transfer characteristics analysis within the embankment dam during seepage was conducted using numerical simulations of heat-flow coupling. Finally, temperature distribution characteristics during steady-state seepage for different water levels were measured, and the relationship between the temperature curve and the phreatic line was obtained. The results demonstrate that accurate temperature detection by OFDR and its high spatial resolution can reflect the characteristics of the temperature field in the seepage model of an embankment dam.

Progress on Heat Transfer in Fractures of Hot Dry Rock Enhanced Geothermal System

Hot Dry Rock (HDR) is the most potential renewable geothermal energy in the future. Enhanced Geothermal System (EGS) is the most effective method for the development and utilization of HDR resources, and fractures are the main flow channels and one of the most important conditions for studying heat transfer process of EGS. Therefore, the heat transfer process and the heat transfer mechanism in fractures of EGS have been the hot spots of research. Due to the particularity of the mathematical models of heat transfer, research in this field has been at an exploratory stage, and its methods are mainly experimental tests and numerical simulations. This paper introduces the progress on heat transfer in fractures of Hot Dry Rock EGS in detail, provides a comparative analysis of the research results and prospects for future research directions: It is suggested that relevant scholars should further study the mathematical equations which are applicable to engineering construction of seepage heat transfer in irregular fractures of the rock mass, the unsteady heat transfer process between multiple fractures of the rock mass and the heat transfer mechanism of the complex three-dimensional models of EGS.

A fully coupled seepage–heat transfer model including a dynamic heat transfer coefficient in fractured rock sample with a single fissure

Conventional seepage–heat transfer models in simulating the heat transfer between fluid and rock in fractures mainly involve one-way coupling and do not consider the influence of temperature on the seepage. Moreover, it is an enormous challenge to define parameters of the explicit heat transfer between the rock and fluid. In order to resolve these shortcomings, a two-way fully coupled model of the seepage–heat transfer in the fractured rock was established in the present study. Based on the original geometric structure of the experimental device, combined with the actual engineering scale, the local dynamic heat transfer coefficient of the fractured rock was established, which is related to the fracture aperture, flow velocity and thermal parameters. Then, the proposed model was verified through the experiment and excellent agreement was achieved in this regard. It was found that the dynamic heat transfer coefficient changes the temperature distribution of fluid and rock in the original static heat transfer coefficient fracture system. The proposed model simplifies the parameters required for the calculation of the heat transfer coefficient. These parameters are related to characteristic variables, such as velocity and rock temperature, and can be simply obtained from standard laboratory tests.

Numerical study on the heat characteristics of a novel artificial seepage thermal storage based on the successive four seasons

Abstract A novel and more efficient artificial seepage thermal storage is proposed to exploit the ground temperature energy. The characteristics of the seepage and heat transfer of the working medium (i.e., water) in the thermal storage are numerically explored, based on the successive four seasons. Under the refrigeration condition in summer, the evolution of the outlet water temperature can be divided into the initial, the cold-reduction and the stable phases with the operating time. Moreover, the influence of the injection flow, as well as the thermal conductivity of the anti-seepage layer, on these characteristics is analyzed. During the temperature recovery period in autumn and spring, 79.4% of the heat at the end of summer is stored until the winter, and 78.8% of the cold capacity at the end of winter is stored to the summer. Under the heating condition in winter, the average heat extraction power, when considering the residual summer heat storage, is 1.4 times higher than that without considering the residual heat. Especially, the artificial seepage heat storage is more suitable for the situation that requires both the refrigeration and the heating. It is expected that this work could offer a new idea to develop the geothermal energy.

Numerical simulation of enhancing coalbed methane recovery by injecting CO2 with heat injection

The technology used to enhance coalbed methane (CBM) recovery by injecting CO2 (CO2-ECBM) with heat, combining heat injection with CO2 injection, is still in its infancy; therefore, theoretical studies of this CO2-ECBM technology should be perused. First, the coupling equations of the diffusion–adsorption–seepage–heat transfer fields of gas are established. The displacement processes under different pressures and temperatures are simulated by COMSOL. Finally, the displacement effects, a comparison of the CO2 storage capacity with the CH4 output and the effective influencing radius of CO2 injection are analyzed and discussed. The results show that (1) the displacement pressure and temperature are two key factors influencing the CH4 output and the CO2 storage capacity, and the increase in the CO2 storage capacity is more sensitive to temperature and pressure than the CH4 output. (2) The gas flow direction is from the injection hole to the discharge hole during the displacement process, and the regions with high velocity are concentrated at the injection hole and the discharge hole. (3) A reduction in the CH4 concentration and an increase in the CO2 concentration are obvious during the displacement process. (4) The effective influencing radius of injecting CO2 with heat increases with the increase in time and pressure. The relationship between the effective influencing radius and the injection time of CO2 has a power exponential function, and there is a linear relationship between the functional coefficient and the injection pressure of CO2. This numerical simulation study on enhancing CBM recovery by injecting CO2 with heat can further promote the implementation of CO2-ECBM project in deep coal seams.

Experimental research on the convection heat transfer characteristics of distilled water in manmade smooth and rough rock fractures

Convection heat transfer characteristics in a single rock fracture was experimentally investigated in this work. Distilled water was used as working medium for heat transfer in manmade smooth and rough fractures of sandstone and granite samples. The influence of fracture surface roughness on heat transfer intensity was analyzed. During seepage heat transfer process, evolution of samples external surface temperatures was monitored using six resistance temperature detectors to study the local heat transfer characteristics along the flow direction. Subsequently, heat transfer correlations were proposed on the basis of the experimental results. The results indicate that the roughness of rock fracture surface improves the overall heat transfer intensity to a certain extent, whereas lithology has little influence on the heat transfer intensity. For smooth fractures, the local heat transfer intensity decreases with the increase of the distance from the inlet. For rough fractures, evolution of sample external temperatures along the flow direction exhibits strong nonlinear characteristics with multiple peaks. Nu/Pr1/3 is close to a power function of Re under the experimental conditions in this work. With the increase of experimental temperature, the relationship gradually tends to be linear.

Seepage Heat Transfer Model and Numerical Simulation of Grate Cooler

Seepage Heat Transfer Model and Numerical Simulation of Grate Cooler

Research on Cooling Mechanism of the Cement Clinker Macroporous Porous Medium

For the cement clinker, a macroporous unconsolidated porous medium, seepage heat transfer theory can more accurately reveal its internal problems. Because of the macroporous characteristics of the cement clinker accumulation body, the changes in the physical properties of the surrounding air, such as viscosity, density, and so on must be taken into consideration in the cooling process of the cement clinker. This article introduces a real gas state equation into the unsteady state seepage equation, and improves the universal local thermal non-equilibrium energy equation, and finally builds a seepage heat exchanger model of the cement clinker accumulation body macroporous porous medium. Using the COTDMA algorithm, this article obtains the unsteady state change progress of the air temperature and the clinker, and the influence of the porosity size on the cooling process, providing a theoretical reference for engineering applications. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res 43(2): 113-123, 2014; Published online 01 July 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21066

Modeling and Solving Problems of Heat Transfer of Cement Clinker

Based on the analysis of heat transfer characteristics of the cement clinker, the porous media’s seepage heat transfer theory is introduced into researching of clinker heat transfer according to its porous media characteristics, and then the control model of cement clinker is built up. Furthermore, this project solves the model by using the finite difference method. At last, the inherent heat transfer law of cement clinker is obtained through simulation.