Underground Temperature Field Research Articles

Understanding of Co-boiling between Organic Contaminants and Water during Thermal Remediation: Effects of Nonequilibrium Heat and Mass Transport.

In situ thermal desorption (ISTD) provides an efficient solution to remediation of soil and groundwater contaminated with nonaqueous phase liquids (NAPLs). Establishing a relationship between the subsurface temperature rise and NAPL removal is significant to reduce energy consumption of ISTD. However, the co-boiling phenomenon between NAPL and water poses a great challenge in developing this relationship due to the nonequilibrium heat and mass transport effects. We performed a systematic experimental investigation into the local temperature rise patterns at different distances from a NAPL pool and under different degrees of superheat by selecting four representative NAPLs (i.e., trichloroethylene, tetrachlorethylene, n-hexane, and n-octane) according to their density and boiling point relative to water. The patterns of temperature rise indicated that the underground temperature field can be divided into three zones: the zone of local thermal equilibrium, the nonequilibrium zone affected by co-boiling, and the zone unaffected by co-boiling. We developed a pattern-recognition-based approach, which considers the effects of local heat and mass transport to establish a qualitative correlation between the temperature rise and NAPL removal. Our results give deeper insights into the understanding of subsurface temperatures in ISTD practice, which can serve as the guideline for more accurate and sustainable remediation.

Research on Performance Test of the Optic-Electric Sensors for Reservoir Landslide Temperature Field Monitoring

In recent years, with the superposition of extreme climate, earthquakes, engineering disturbance and other effects, global landslide disasters occur frequently. Due to reservoir landslides being mostly in a multi-field coupling environment, the temperature field will impact the deformation and seepage fields, thereby affecting the stability of the reservoir landslide. The variation in the landslide’s surface temperature also directly affects the stress and deformation of deep rock masses. If hidden dangers are not detected in time, and corresponding measures are implemented, it is easy to cause landslide instability. In order to clarify the temperature measurement performance of different optic-electric sensors and the application characteristics of layout techniques, laboratory calibration tests of temperature sensors under different adhesives and attachment materials are carried out in this paper. It was found that the test data of the iron bar had the best effect among the four attachment materials overall. Therefore, the bar with a high-stiffness material should be preferred when selecting a pipe fitting as the fiber Bragg grating (FBG) temperature attachment in the borehole. However, considering the high requirements for the durability of sensors and layout techniques in on-site monitoring, the long-term stability of the adhesives used in actual monitoring needs to be improved. At the same time, it was found that the platinum 100 (PT100) temperature sensor has relatively higher testing accuracy (A: 0.15 + 0.002 × |t|; B: 0.30 + 0.005 × |t|), a larger temperature measurement range (−200~+850 °C) and better temperature measurement stability when compared to conventional sensors. Moreover, its resistance value has a good linear relationship with temperature. Finally, the Xinpu landslide in the Three Gorges Reservoir area was selected as the research object for on-site monitoring. There was a high correlation between the on-site monitoring results with the laboratory calibration test results. Therefore, through the performance test of optic-electric sensors in reservoir landslide temperature fields, more accurate solutions can be provided for selecting sensors and designing layout techniques to monitor the underground temperature field of landslides under different geological conditions. Thereby, grasping the real-time state information of the reservoir landslide temperature field is achieved accurately, providing an important reference for early warning, prediction, prevention and the control of reservoir landslide disasters.

Application of SAGD technology in the development of super heavy oil reservoir buried medium deep

Continental super heavy oil reservoirs in China are characterized by deep burial depth, strong reservoir heterogeneity and high oil viscosity. The steam huff and puff technology are used to develop this type of reservoir, but in this development method, its oil recovery rate, oil steam ratio, and ultimate recovery are low. The benefit of the reservoir development is losses in this high cost per ton of oil. Many vertical wells injecting steam and one horizontal well-producing liquids pattern of SAGD technology (abbreviated as VERTIHORIONATAL pattern SAGD) were Innovated to solve the problems based on SAGD technology introduced from Canada. The SAGD technology introduced in Canada was made of double horizontal wells. The above horizontal well injects steam and the other horizontal well produces liquids continued (abbreviated as DOUBLE HORIZONTAL pattern SAGD). The VERTIHORIONATAL SAGD technology makes full use of the original well pattern of huff and puff and takes advantage of the thermal connectivity and underground temperature field formed by early development; At the same time, the VERTIHORIONATAL pattern SAGD technology can effectively solve the problem of steam cavity uneven expansion caused by reservoir heterogeneity by adjusting the location of steam injection vertical wells. It can also balance the liquid production in good horizontal sections and improve steam cavity formation speed by adjusting steam injection well sections and steam injection parameters. The technology has been successfully applied in the medium-deep super heavy oil reservoir in the Shu-1 area, Du84 block, Liaohe Oilfield. Seven oil wells with a daily output of 100 tons have been cultivated, and a stable production of million tons for four consecutive years. It has been built as China’s largest SAGD development demonstration area for medium-deep super-heavy oil.

Study on the simulation and optimization of the heat transfer scheme in a buried-pipe ground-source heat pump

To guarantee the sustainable development and utilization of shallow geothermal energy and avoid heat accumulation problems during the operating period of ground-source heat pump, a three-dimensional coupled numerical model of unsteady groundwater seepage and heat transfer was established. This model was applied to the demonstration project of the buried-pipe heat pump system in Danyang, Jiangsu Province. The model was based on the principles of groundwater seepage and heat transport and was combined with the future operating conditions of the ground-source heat pump system, to forecast the thermal equilibrium development trend of underground temperature field. A design scheme was determined on this basis. The district was divided into five development and utilization zones (I–V), and we changed the minimum heat transfer hole spacing from 5 to 14, 17, 18, 21, and 19 m. From the results, according to the actual situation we adopted, the simulation optimization scheme effectively slowed the heat transfer and resolved the heat accumulation problem, which can easily occur during the operation of a ground-source heat pump system. The three-dimensional coupled numerical model of unsteady groundwater seepage and heat transfer is an effective way to optimize and determine the sustainable development and utilization plan of a ground-source heat pump for shallow geothermal energy.

Parameter analysis of single U-tube GHE and dynamic simulation of underground temperature field round one year for GSHP

Abstract Based on a quasi 3-D steady model inside and a 2-D unsteady model outside of the borehole of ground heat exchanger(GHE), the relationship between the heat exchange rate per depth of borehole and main parameters (center-to-center distance of two branch pipes, radius and depth of the borehole) has been analyzed. The rational values of those design parameters with considering the heat exchange rate per depth of borehole are obtained. The dynamic simulations of underground temperature field (UTF) of single-pipe and pipe-group of U-tube GHE have been conducted by ANSYS. The change rules of UTF are obtained when ground source heat pump(GSHP) has experienced a complete cooling and heating cycle during one year. The simulation results of a single-pipe show that the action radius of borehole is 1.9 m, i.e., it is reasonable that the borehole center-to-center distance is 3.8 m. The simulation results of pipe-group indicate that temperature of the soil center encircled by four boreholes at the beginning of heating in winter is higher than the initial temperature of soil, but it is in opposite for cooling in summer, which is beneficial to the efficient operation of GSHP. This work can provide guidance for the rational design and operation of GSHP.

The coupling effect of ventilation and groundwater flow on the thermal performance of tunnel lining GHEs

Tunnel lining ground heat exchangers (GHEs) in this paper have advantages such as not requiring extra space, a low construction cost, and more efficient in heat exchange, offering a solution to the utilization of geothermal energy in central urban areas. Ventilation and groundwater flow are two important factors that significantly affect the underground temperature field. Laboratory model tests were carried out to evaluate the coupling effect of ventilation and groundwater flow on the thermal performance of tunnel lining GHEs. The test results show that (i) ventilation enhances the heat exchange process between the GHEs and the surrounding rock; (ii) the depth to which the GHEs influence the surrounding rock temperature field in the downstream of the groundwater flow field is 2.6 times higher than that in the upstream, and the ventilation and groundwater flow aggravate uneven distribution of the temperature field of the surrounding rock, so the heat exchange pipes should be installed in the upstream of the groundwater flow field; (iii) the coupling heat transfer between air and lining should be taken into consideration when the heat exchange rate of the heat exchange pipe is calculated.

Design and Experimental Testing of a Ground Source Heat Pump System Based on Energy-Saving Solar Collector

AbstractA ground source heat pump system can cause the fluctuation of the underground temperature field in the working process. If this system is used for a long time, the “heat accumulation” phenomenon will occur, the unit coefficient of performance (COP) value will be reduced, and the system energy consumption will be increased. In order to solve this problem, a new type of heat storage of solar and ground source heat pump coupling system was developed in this paper. The solar collector system can achieve high quality heating seasonal storage, i.e., high quality heating in winter and high quality cooling in summer. The falling film evaporation process was adopted to obtain efficient refrigeration. The experimental results show that the buried tube heat exchanger and the intermittent heat storage tank can operate well in the system. In addition, the COP value of the system is 6.96, which demonstrates that the working efficiency of the designed solar ground source heat pump system is high. The working eff...

Predicting initial formation temperature for deep well engineering with a new method

With the progress of science and technology, human beings explore the energy underground with thousands of meters. As a thermophysical parameter, initial formation temperature (IFT) plays an essential role in deep well engineering. However, it is not easy to predict the IFT accurately before drilling. This work uses a new method to analyze the effect factors of the underground temperature field, and assumes an artificial surface to eliminate the disturbance of the human errors and equipment errors on the surface temperature and thermal conductivity. Considering different distributions of the formation thermal conductivity and the rock radiogenic heat production, an optimized model was established. With this model, the paper predicted the bottom temperature of the main hole of the Chinese Continental Scientific Drilling (CCSD) as 132.80 °C at 4 725 m depth with 0.5% error. When the thermal conduction is dominant in the formation, this simple method can predict the IFT distribution effectively for deep well in the exploration stage. However, it is almost impossible to avoid aquifers in the formation of drilling deep well, an existing drillhole including groundwater is needed to predict for testing the model’s accuracy.

Analyses of the Suitability of Ground-Source Systems in Typical Architecture in Northern Region

The aim of study was to measure the suitability and energy saving of soil source heat pump. We established a tube group model of underground temperature field in 20 years. Take three typical architecture--tavern, office and hotel buildings for example, used the primary energy ratio--one index about energy-savingas the main target of comparison, then took the technical indicators soil cumulative temperature into account. The result shows that the shopping malls in Beijing is the best grade of the applicability about the soil source heat pumps application, followed by hotel and office building is the worst.

Numerically simulating the thermal behaviors in groundwater wells of groundwater heat pump

In the geothermal energy utilization of a closed loop groundwater system of a GWHP (groundwater heat pump) and an ATES (aquifer thermal energy storage), thermal breakthrough is a very important aspect in the design of these systems. It can cause a gradual variation in the temperature of the pumping water and impact the efficiency of the GWHP. For pumping and injecting well groups, the influence of groundwater flow on the heat transfer is particularly important, especially for the aquifers with high porosity and hydraulic conductivity, the direction and velocity of groundwater directly affects the underground temperature field evolution. In this research, heat-water transfer numerical simulation and experiment has been conducted to study the evolution rule between aquifer temperature field and groundwater flow field. Simulation results were compared with the experimental results, and the validity of the simulation model was confirmed. Furthermore, the effects of groundwater flow on pumping average temperature and thermal breakthrough have been estimated by the numerical analysis, which will serve as a basis for the engineering design and further study of GWHP system.

Evaluation of ground thermal properties and specification of the geological structure using thermal response test, natural gamma, and resistivity data

The primary objective of this study is to identify the ground thermal properties of the local geological structure and to investigate the geological structure. The knowledge of underground thermal properties is necessary to design borehole heat exchangers (BHE) for Ground Source Heat Pumps (GSHP). Particularly for commercial GSHP, main thermal parameters should be measured on site. A thermal response test (TRT) is performed on one or more borehole heat exchangers in a pilot borehole. This borehole is a part of the borehole field. A TRT enables to collect the data to be used for ground thermal parameters calculation, i. e. the thermal conductivity and resistivity. The heat load to be injected into the BHE is predefined in advance; the resulting temperature changes of the circulating fluid and flow rate are measured. The paper presents a short description of the basic concept and theory of TRT, shortly reviews the experience of this technology. The main aim of the presented study and calculations is to start creating efficient methodology to estimate main thermal parameters (thermal conductivity and thermal resistance) in Lithuania. The most used line-source methods and the results will be presented and compared against the numerical method. Circulating fluid and borehole temperatures would be analytically calculated in order to estimate the impact on the underground temperature field.

Simulation Analysis of Groundwater Source Heat Pump’s Underground Temperature Field Changes under Different Pumping and Injecting wells Modes

Through the establishment of the coupled model of groundwater flow and temperature, the changing tread of groundwater temperature and the basic characteristics of thermal breakthrough under the different layout wells modes were simulated and analyzed. The results showed that, the similar wells distance didn’t affect the thermal breakthrough significantly, the distance of pumping wells and irrigating wells affected pumping temperature significantly and thermal breakthrough. The more number of pumping and injecting didn’t extend the time of thermal breakthrough, and didn’t affect pumping temperature significantly from the results of long-running, the layout pattern of wells with one pumping and two injecting presented significant advantages in practical engineering.

Study on Match and Running Features of Heat Multi-Level Shunt Ground Source Heat Pump System in the Hot Summer and Warm Winter Areas

Annual cold heat adjustment is one of the key problems in the practical application of ground-source heat pump system. According to the energy-consuming characteristics of the building in hot summer and warm winter area zone and engineering practice, the author puts forward the multi-level heat shunt ground source heat pump systems(GSHPS). Reasonable system can be matched according to the characteristics of the cold water chiller and the water source heat pump, which takes full advantages of soil cold/heat source, improves the efficiency of the soil heat exchanger, and balances underground temperature field effectively.

Thermal performances of different types of underground heat exchangers

An experiment system with different types of U-vertical ground coupled heat exchanger (UGCHE) in situ was set up, for example, single or double U-pipes with sandstone backfills, and single U-pipe with cement backfills. Experiments on the thermal performance of UGCHE were carried out in different conditions, such as different inlet temperature, flow rate, soil types, backfill materials, number of U-pipes and the different operation modes. In theory, an inner heat source model was adopted, and the simulation has been done for the underground temperature field with professional porous medium software.

Inner heat source model with heat and moisture transfer in soil around the underground heat exchanger

This paper presents an inner heat source model of underground heat exchanger based on the heat and mass transfer theory in soil. A number of factors such as moisture movement in soil, soil type, and soil property were taken into account in the model. The underground heat exchanger was simplified as the equivalent inner heat source term in the model. The software of Autough2 was used to conduct the numerical simulations. And the paper presents the analyses on the influences of different soil properties and different operation modes on the underground temperature field around the single U-vertical underground heat exchanger.

80,000 years ground surface temperature history inferred from the temperature–depth log measured in the superdeep hole SG-4 (the Urals, Russia)

Temperature and thermal conductivity data obtained from the Ural superdeep borehole SG-4 (58°24′N Lat., 59°44′E Long., Middle Urals, Russia) is used to assess ground surface temperature history (GSTH) over the past 80,000 years. GSTH is estimated by solving the one-dimensional heat conduction equation for a homogeneous semi-infinite medium and by comparing the solution with the measured temperatures by means of least square method. The resolution power of paleoclimate signal in the underground temperature field is theoretically studied and a parameter “relative duration” of the climatic event has been introduced. Relative duration is equal to η=( t s −t f)/ t s, where t s and t f are the times before temperature logging of the beginning and end of a climatic event. Only events with η≥0.5 can be resolved from the temperature field. The reconstructed history reveals a number of past climatic events. These include the end of the Wurm glaciation and warming at the beginning of Holocene about 10,000 years ago, Holocene Optimum 4000–6000 years ago, Medieval Warm Period with a culmination about 1000 years ago and Little Ice Age 200–500 years ago. The amplitude of postglacial warming (12–13 K) inferred from the underground temperatures is greater than previously estimated. It is assumed that surface temperature variation amplitude is a function of the combined effects of surface air temperature changes and snow thickness changes. Statistical relations between mean annual soil–air temperature difference and snow cover thickness are proposed.