Search Results (37)

In the production process of horizontal wells, wellbore temperature data play a critical role in predicting shale gas production. This study proposes a coupled thermo-hydro-mechanical (THM) mathematical model that accounts for the influence of the stress field when determining the distribution of wellbore temperature. The model integrates the effects of heat transfer in the temperature field, gas transport in the seepage field, and the mechanical deformation of shale induced by the stress field. The coupled model is solved using the finite difference method. The model was validated against field data from shale gas production, and sensitivity analyses were conducted on seven key parameters related to the stress field. The findings indicate that the stress field exerts an influence on both the wellbore temperature distribution and the total gas production. Neglecting the stress field effects may lead to an overestimation of shale gas production by up to 12.9%. Further analysis reveals that reservoir porosity and Langmuir volume are positively correlated with wellbore temperature, while permeability, Young’s modulus, Langmuir pressure, the coefficient of thermal expansion, and adsorption strain are negatively correlated with wellbore temperature. Full article

To address the hydrogeological parameters of polluted sites at the site scale, a series of physical and numerical simulation experiments were conducted to investigate seepage and solute transport under the influence of various physical fields. These experiments utilized an experimental platform designed for the acquisition of pollutant transport and transformation data, which incorporated three-dimensional multifield coupling, alongside a numerical model that also accounted for multiphysical field interactions. The numerical simulations employed Darcy’s law, the heat conduction equation, and convective–dispersive equations to analyze the seepage field, heat transfer, and solute transport processes, respectively. The findings from both physical and numerical tests indicate that variations in groundwater temperature and solute concentration significantly influence solute transport dynamics. Specifically, an increase in groundwater temperature correlates with an accelerated migration rate of sodium chloride (NaCl) solute, resulting in a reduced time for the solute to achieve equivalent concentrations in observation wells. Conversely, when the concentration of NaCl in groundwater rises, the temperature of the groundwater also increases when the solute reaches the same concentration in the observation wells. This phenomenon can be attributed to the decrease in the specific heat capacity of groundwater with higher solute concentrations. Moreover, as the concentration of sodium chloride in groundwater increases, the rate of temperature elevation in the groundwater accelerates due to a decrease in specific heat capacity associated with higher solute concentrations, thereby requiring less thermal energy for the groundwater to attain the same temperature. The results further reveal that the hydraulic conductivity of the target aquifer, specifically the pulverized clay layer, ranges from 6.72 to 8.52 × 10⁻⁶ m/s, with an effective thermal conductivity of 2.2 W/(m·K), a longitudinal dispersion of 0.554 m, and a transverse dispersion of 0.05 m. Full article

As a shallow geothermal energy development technology, energy pile contributes to sustainable development. The seepage effect has a positive effect on the heat transfer performance of the energy pile, and the heat transfer efficiency of the energy pile can also be improved by optimizing the operation strategy. Combined with the structural characteristics of the deep-buried energy pile, the heat transfer characteristics of the deep-buried energy pile are analyzed under continuous and intermittent operation conditions, and the effect of seepage on the heat transfer performance is further investigated under the intermittent operation mode. The results show that the long-term operation of the deep-buried energy pile will reduce its heat exchange performance and aggravate the heat accumulation phenomenon inside the pile body, and the intermittent operation can maintain a higher instantaneous heat exchange rate (HER) in the long-term operation compared with the continuous operation. Considering the energy demand, when the intermittent ratio is 5, the average HER of the pile body only decreases by 68.93 W, and the overall energy efficiency of the pile body is improved by 7.7%. Combined with the operating effects of different intermittent ratios, the optimal range of the circulating medium flow rate for deep buried pipe energy piles should be selected from 1.0 m³/h to 1.2 m³/h. Groundwater seepage can weaken the degree of heat accumulation inside the DBP-EP piles and improve the overall heat exchange efficiency of DBP-EP, and combined with the intermittent operation mode will be able to further alleviate the DBP-EP heat buildup. The two factors promote each other and have a positive impact on the piles, positively affecting the soil’s long-term heat exchange. Full article

The development of nanofluid-assisted heavy oil extraction can address critical challenges in global energy sustainability, particularly for ultra-heavy oil reserves characterized by high viscosity and low permeability. This study investigates the dual role of hydrophobic nanofluids in enhancing reservoir permeability and heat transfer efficiency. Through advanced triaxial shear seepage experiments and heat transfer experiments, the permeability and thermal conductivity of oil sands cores treated with hydrophobic silica-based nanofluids (0–0.15 wt%) were quantitatively analyzed. The results showed that the permeability increased by up to 536.59% (from 33.18 mD to 211.22 mD) after nanofluid treatment, which was attributed to nanoparticle-induced pore throat modification and reduced interfacial tension. At the same time, the thermal conductivity has increased by up to 132% (from 0.25 W/m·K to 0.58 W/m·K), significantly improving the heat transfer efficiency. There is a linear relationship between the concentration of nanofluids and the thermal conductivity, and the relationship between the thermal conductivity, and the strain of oil sands is established. This work provides a scientifically grounded framework for scaling nanofluid applications in field trials, offering a transformative pathway to reduce energy intensity and improve recovery rates in ultra-heavy oil exploitation. Full article

Hydraulic fracturing is a critical process in the development of oil shale reservoirs. The presence of widespread bedding planes and natural fractures significantly influences the propagation of hydraulic fractures. Additionally, the injection point density plays a crucial role in the effectiveness of reservoir reconstruction. The Global Embedded Cohesive Zone Method (FEM-CZM) was employed to model the initiation and propagation of fractures from perforation holes, considering the combined effects of bedding planes and natural fractures. The results indicate the following: (1) the initiation and propagation of fractures from perforation holes lead to the co-propagation of two to four asymmetric main fractures, alongside open bedding planes and natural fractures; (2) larger bedding plane thickness and smaller bedding plane spacing promote hydraulic fractures’ tendency to propagate along the bedding planes, resulting in longer fracture lengths and predominance of tensile failure; and (3) a higher in situ stress difference facilitates the fracture’s penetration of the bedding plane, leading to an initial increase and subsequent decrease in fracture length. Tensile failure remains dominant, while the proportion of shear failure increases. Based on these findings, it is recommended to select fracturing sites with thicker bedding planes, larger bedding plane spacing, and a smaller vertical in situ stress field. Additionally, a perforation scheme with six injection points should be adopted to enhance the formation of high-efficiency seepage and heat transfer channels between hydraulic fractures, bedding planes, and natural fractures. Full article

Taking the Sanya River Mouth Channel project as a case study, this research explores the minimum brine temperature required for the pipe-jacking freezing method during staged freezing. Based on the heat transfer theory of porous media, a three-dimensional model of the actual working conditions was established using COMSOL 6.1 finite element software. By adjusting the brine cooling scheme, the development and distribution patterns of the freezing curtain under different brine temperatures were analyzed. The results indicate that as the staged freezing brine temperature increases, the thickness of the freezing curtain decreases linearly, and the closure of isotherms is inhibited. When the brine temperature is −8 °C, the thickness of the freezing curtain meets the minimum requirement and effectively achieves the freezing effect under both low and high seepage flow conditions. Additionally, seepage significantly affects the formation of the freezing curtain, causing it to shift towards the direction of seepage, with the degree of shift becoming more pronounced as the seepage velocity increases. When the seepage velocity is so high that the thickness of the freezing curtain on one side is less than 2 m, the impact of seepage on the freezing curtain can be reduced by decreasing the hydraulic head difference in the freezing area or by increasing the arrangement of freezing pipes, thereby enhancing the freezing effect. Full article

This study investigated the thermo-hydrodynamic groundwater environment of a sandy beach where a unique sand bathing method attracts many visitors. The discussed temperatures covered a wide range, from the normal to the boiling temperature of water. We, at first, examined the feasible conditions for sand bathing and found that the volumetric water content was the crucial factor. Comprehensive field observations were implemented to elucidate two physical quantities: the groundwater flow and the temperature in the sand layer. The latter one was found to be governed by the groundwater level and tidal fluctuations. The characteristics obtained were found to be consistent with the feasible conditions in the landward area. While in the offshore area, the temperature was proved to have suddenly dropped. These results strongly suggest that the underground heat source is distributed in specific spots. A numerical model to describe the groundwater flows and the heat transfer mechanism was developed based on a saturated/unsaturated seepage flow model. The computational results were found to adequately reproduce the observed spatial temperature distribution. The reproduction ability of the model was found to be limited in terms of temporal variations; it was good for the groundwater level, but not for the temperature in the sand. Full article

Ground source heat pump (GSHP) systems have been widely used in the field of shallow geothermal heating and cooling because of their high thermal efficiency and environmental friendliness. A borehole heat exchanger (BHE) is the key part of a ground source heat pump system, and its performance and investment cost have a direct and significant impact on the performance and cost of the whole system. The ground temperature gradient, air temperature, seepage flow rate, and injection flow rate affect the heat exchange performance of BHEs, but most of the research on BHEs lacks field test verification. Therefore, this study relied on the results of a field thermal response test (TRT) based on a distributed optical fiber temperature sensor (DOFTS) and site hydrological, geological, and geothermal data to establish a corrected numerical model of buried pipe heat transfer and carry out the heat transfer performance analysis of a buried pipe in the heating season. The results showed that the ground temperature gradient of the test site was about 3.0 °C/100 m, and the temperature of the constant-temperature layer was about 9.17 °C. Increasing the air temperature could improve the heat transfer performance. The temperature of the surrounding rock and soil mass of the single pipe spread uniformly, and the closer it was to the buried pipe, the lower the temperature. When there is groundwater seepage, the seepage carries the cold energy generated by a buried pipe’s heat transfer through heat convection to form a plume zone, which can effectively alleviate the phenomenon of cold accumulation. With an increase in seepage velocity, the heat transfer of the buried pipe increases nonlinearly. The heat transfer performance can be improved by appropriately reducing the temperature and velocity of the injected fluid. Selecting a backfill material with higher thermal conductivity than the ground body can improve the heat transfer performance. These research results can provide support for the optimization of the heat transfer performance of a buried tube heat exchanger. Full article

It is very important for embankment engineering to consider the seepage factor. If the potential seepage is not discovered in time and seepage control measures are not appropriate, seepage is very likely to cause damage and deformation, resulting in embankment failure. Based on temperature and seepage fields theories, a temperature–seepage coupled model is established in this paper. It is combined with a distributed temperature sensing (DTS) system to measure the temperature field of the porous media. This approach allows for the inversion of the inner seepage field, realizing the real-time monitoring of embankment health to ensure its safety and long-term operation. According to the coupling analysis on the temperature–seepage fields, for practical engineering, the influence of temperature on the seepage field is small and neglectable. Only the effect of the seepage field on the temperature field is considered. The DTS optical fiber temperature measurement system is widely used in various projects nowadays because of its high stability and efficiency advantages. The optical fiber is sensitive to temperature and can give fast and accurate temperature feedback regarding seepage location. Combined with the Heat Transfer Module in COMSOL, the multi-line heat source method can be used to invert the seepage field according to the temperature field of the porous medium inside the embankment and derive the seepage flow rate of the stable seepage field. For unstable seepage, optical fiber is good at seepage measuring and location detecting. For different practical engineering, a different heating power can be used for different seepage conditions. By monitoring the temperature change, the seepage condition can be inverted which is one of the indicators for evaluating engineering safety. Full article

Backfill material used as a heat-transfer medium in boreholes of ground heat exchangers (GHEs) has a great influence on heat-transfer efficiency. Abandoned waste material causing environmental pollution has become a key issue around the world. To make full use of solid waste, backfill material made of waste fly ash in combination with graphite of high thermal conductivity was proposed. First, the thermal properties of cement/fly ash blended with different mass ratio of graphite were tested through laboratory tests. Then, a numerical model was established, in which the accuracy was validated based on a field test. Finally, an investigation of the long-term performance (over a period of 90 days) for four boreholes backfilled with natural sand, cement/fly ash, and cement/fly ash combined with different proportions of graphite was conducted through this numerical model, and the heat-transfer rates under constant inlet temperature in four boreholes decreased from 13.31, 44.97, 45.95, and 46.73 W/m to 14.18, 14.96, 15.66, and 16.19 W/m after the 90-day operation. Considering the influence of groundwater seepage, the horizontal groundwater flow had a positive impact, improving the long-term heat-transfer performance. The heat-transfer rates of four testing boreholes decreased from 44.46, 46.38, 47.22, and 47.68 W/m to 21.18, 21.93, 22.62, and 23.13 W/m. However, long-term groundwater seepage in a vertical direction caused a sharp decrease in the heat-transfer rate, and the values after 90 days were 10.44, 10.62, 10.78, and 10.81 W/m, which were the lowest of all the working conditions. The feasibility of using fly ash blended with graphite as backfill material was further validated through a comprehensive perspective, including indoor laboratory, field testing, and numerical simulation, which has rarely been conducted in previous research. Full article

This paper takes the freezing project of the North Arch Tunnel of the Hong Kong–Zhuhai–Macao Bridge as an example. Based on Darcy’s law and the theory of heat transfer in porous media, using the coupled module of the temperature field and seepage field in the COMSOL Multiphysics software, numerical simulations of the freezing reinforcement of the new pipe curtain freezing method are conducted to study the influence of different factors on this method under seepage conditions. The research shows that an increase in the groundwater flow velocity will affect the development of frozen soil curtains, prolonging the formation time of frozen soil curtains. A rise in the initial ground temperature will increase the time required for the formation of frozen soil curtains during the freezing process, resulting in a slight increase in the temperature of the final frozen soil curtains. With an increase in the salinity of the groundwater, the temperature at the temperature measurement point upstream of the freezing pipe increases, while the temperature at the temperature measurement point downstream of the freezing pipe decreases. The average temperature of the frozen soil curtain also increases with an increase in the salinity of the groundwater. This study is expected to provide a valuable reference for similar projects in the future. Full article

Marine gas hydrate formations are characterized by considerable water depth, shallow subsea burial, loose strata, and low formation temperatures. Drilling in such formations is highly susceptible to hydrate dissociation, leading to gas invasion, wellbore instability, reservoir subsidence, and sand production, posing significant safety challenges. While previous studies have extensively explored multiphase flow dynamics between the formation and the wellbore during conventional oil and gas drilling, a clear understanding of wellbore stability under the unique conditions of gas hydrate formation drilling remains elusive. Considering the effect of gas hydrate decomposition on formation and reservoir frame deformation, a multi-field coupled mathematical model of seepage, heat transfer, phase transformation, and deformation of near-wellbore gas hydrate formation during drilling is established in this paper. Based on the well logging data of gas hydrate formation at SH2 station in the Shenhu Sea area, the finite element method is used to simulate the drilling conditions of 0.1 MPa differential pressure underbalance drilling with a borehole opening for 36 h. The study results demonstrate a significant tendency for wellbore instability during the drilling process in natural gas hydrate formations, largely due to the decomposition of hydrates. Failure along the minimum principal stress direction in the wellbore wall begins to manifest at around 24.55 h. This is accompanied by an increased displacement velocity of the wellbore wall towards the well axis in the maximum principal stress direction. By 28.07 h, plastic failure is observed around the entire circumference of the well, leading to wellbore collapse at 34.57 h. Throughout this process, the hydrate decomposition extends approximately 0.55 m, predominantly driven by temperature propagation. When hydrate decomposition is taken into account, the maximum equivalent plastic strain in the wellbore wall is found to increase by a factor of 2.1 compared to scenarios where it is not considered. These findings provide crucial insights for enhancing the safety of drilling operations in hydrate-bearing formations. Full article

As a typical unconventional energy reservoir, natural gas hydrate is believed to be the most promising alternative for conventional resources in future energy patterns. The exploitation process of natural gas hydrate comprises a hydrate phase state, heat and mass transfer, and multi-phase seepage. Therefore, the study of heat transfer characteristics of gas hydrate is of great significance for an efficient exploitation of gas hydrate. In this paper, the research methods and research progress of gas hydrate heat transfer are reviewed from four aspects: measurement methods of heat transfer characteristics, influencing factors of heat transfer in a hydrate system and hydrate-containing porous media systems, predictive models for effective thermal conductivity, and heat transfer mechanisms of hydrate. Advanced measurement techniques and theoretical methods that can be adopted for the heat transfer characteristics of gas hydrate in the future are discussed. Full article

The study of the seepage and heat transfer law of three-dimensional rough fractures is of great significance in improving the heat extraction efficiency of underground thermal reservoirs. However, the phase transition effects of fluids during the thermal exploitation process profoundly influence the intrinsic mechanisms of fracture seepage and heat transfer. Based on the FLUENT 2020 software, single-phase and multiphase heat–flow coupling models were established, and the alterations stemming from the phase transition in seepage and heat transfer mechanisms were dissected. The results indicate that, without considering phase transition, the geometric morphology of the fractures controlled the distribution of local heat transfer coefficients, the magnitude of which was influenced by different boundary conditions. Moreover, based on the Forchheimer formula, it was found that the heat transfer process affects nonlinear seepage behavior significantly. After considering the phase transition, the fluid exhibited characteristics similar to shear-diluted fluids and, under the same pressure gradient, the increment of flow rate was higher than the increment in the linearly increasing scenario. In the heat transfer process, the gas volume percentage played a dominant role, causing the local heat transfer coefficient to decrease with the increase in gas content. Therefore, considering fluid phase transition can more accurately reveal seepage characteristics and the evolution law. Full article

Some dams globally have negatively affected downstream structures. Constructing subsidiary weirs may solve this problem. This novel study focuses on investigating the parameters of seepage beneath the original structure and the proposed subsidiary weir. Conformal mapping and finite element methods are used for the analysis. The proposed subsidiary weir consists of a sloping central apron, flat aprons on both the downstream and upstream ends, and upstream and downstream sheet piles of varying depths. The existing structure also has sheet piles of different depths at its upstream and downstream ends, with an impervious layer situated at a specific depth below both the structures. The study derives equations for the simulation of the upwards pressure on both the structures, seepage rate, and exit gradient along the downstream bed and the filter at an intermediate location. Our own developed software for the analysis and a commercial software for numerical methods named Finite Element Heat Transfer (FEHT)-version-1are used to calculate these parameters. The accuracy of the analytical and numerical methods is verified by comparing the results with experimental data, which demonstrate a good level of agreement. This study also simulates the impacts of various factors, such as sheet pile configurations, the depth of the stratum beneath the structure, the ratio of effective heads, and the length of the intermediate filter. Full article