Borehole Depth Research Articles

Impact of Temperature on the Performance of Plasma-Pulse Geo-Drilling (PPGD)

Advanced Geothermal Systems (AGS) may in principle be able to satisfy the global energy demand using standard continental-crust geothermal temperature gradients of 25–35 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C/km. However, conventional mechanical rotary drilling is still too expensive to cost-competitively provide the required borehole depths and lengths for AGS. This highlights the need for a new, cheaper drilling technology, such as Plasma-Pulse Geo-Drilling (PPGD), to improve the economic feasibility of AGS. PPGD is a rather new drilling method and is based on nanoseconds-long, high-voltage pulses to fracture the rock without mechanical abrasion. The absence of mechanical abrasion prolongs the bit lifetime, thereby increasing the penetration rate. Laboratory experiments under ambient-air conditions and comparative analyses (which assume drilling at a depth between 3.5 and 4.5 km) have shown that PPGD may reduce drilling costs by approximately 17–23%, compared to the costs of mechanical drilling, while further research and development are expected to reduce PPGD costs further. However, the performance of the PPGD process under deep wellbore conditions, i.e., at elevated temperatures as well as elevated lithostatic and hydrostatic pressures, has yet to be systematically tested. In this paper, we introduce a standard experiment parameter to examine the impact of deep wellbore conditions on PPGD performance, namely the productivity (the excavated rock volume per pulse) and the specific energy (the amount of energy required to drill a unit volume of rock). We employ these parameters to investigate the effect of temperature on PPGD performance, with temperatures increasing up to 80 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C, corresponding to a drilling depth of up to approximately 3 km.

Transient heat transfer simulation, sensitivity analysis, and design optimization of shallow ground heat exchangers with hollow-finned structures for enhanced performance of ground-coupled heat pumps

Ground-Coupled Heat Pumps (GCHPs) are regarded as an effective technology for building energy development and residential hot water production. The essential challenges to encompass these systems in urbanized areas are the highly drilling and initial costs of GCHPs. To overcome this challenge, researchers and industries are seeking innovative solutions by focusing on optimizing the structure of ground heat exchangers (GHXs), which act as the essential component for efficient geothermal energy extraction in GCHPs. Hence, this paper introduces a comprehensive comparative numerical investigation of an innovative U-tube GHX with a hollow-finned structure for augmenting the performance of the GCHPs. This design remarkably enhances the thermal performances, reduces the thermal resistance, therefore minimizes borehole depth, reduces drilling costs, boosts GCHP's financial viability, and bolsters geothermal energy utilization. Therefore, a series of three-dimensional analyses of transient heat extraction is executed and validated using a practical field experiment performed by the authors' research group to investigate the thermal behavior of the hollow-finned U-tube GHX at different fin configurations and compare its efficacy to typical circular U-tube GHX. More so, a parametric study and sensitivity analysis are also performed to identify the influence of critical operational and design factors on the heat extraction of the proposed hollow-finned U-tube GHX compared to the typical circular GHX. The influences of groundwater flow on the transient heat extraction were also examined. Additionally, a dimensionless shape factor is introduced to assess the implications of the U-tube geometry with hollow-finned on the thermal performance of the GHXs. Furthermore, design optimization was also conducted by examining different branched-shaped hollow-fin's U-tube GHX configurations. The findings indicate that the mean heat transfer rate of hollow-finned U-tube GHX can be increased by 44.58 % compared to the conventional circular U-tube GHX. Correspondingly, the total thermal resistance of hollow-finned U-tubes GHX was reduced by 47.71 %. It also identified that the Y-shaped hollow-finned U-tube GHX was the optimal design among the investigated configurations of branched-shaped hollow-finned U-tube GHXs, demonstrating an increase of 52.64 % compared to the conventional circular U-tube GHX. Moreover, it is revealed that a lower shape factor enhances the heat transfer rate significantly. Furthermore, the optimal mass flow rate and desired number of hollow-finned were estimated as 0.80 kg/s and six fins, respectively. Conclusively, this investigation concludes that the hollow-finned U-tube GHX can greatly enhance the heat extraction rates and reduce borehole thermal resistance, which can increase the efficiency of GCHP systems.

Investigation of Groundwater Quality with Borehole Depth in the Basin Granitoids of the Ashanti Region of Ghana

Investigation of Groundwater Quality with Borehole Depth in the Basin Granitoids of the Ashanti Region of Ghana

An Assessment of Deep Borehole Disposal Post-Closure Safety

Around the world, deep borehole disposal is being evaluated for intermediate level-waste (ILW), high-level waste, and spent nuclear fuel. To facilitate a disposal concept options analysis for ILW in Australia, desktop and lab-based geoscientific investigations, together with generic post-closure safety assessments of deep borehole disposal of long-lived ILW, have been undertaken. This paper reports on geoscientific data obtained on crystalline rock and rock salt as model rocks for geological disposal. Petrophysical and mineralogical properties for these rocks have been investigated to provide realistic data for evaluation and input to post-closure safety assessments. For crystalline rock samples originating from depths between 700 to 1900 m, very low hydraulic conductivity (2 × 10−12 to 3 × 10−11 m/s) and very low porosity (0.02% to 1.2%) were obtained. The noble gas isotopic composition of fluid inclusions from the same depth interval confirmed the rock had been devoid of recent interaction with meteoric water, thus providing potentially suitable conditions for geological disposal. Rock salt from a 802-m (heterogeneous sample with 40% halite) and a 1100-m (sample with 98% halite) depth also had a low hydraulic conductivity (5 × 10−10 to 5 × 10−9 m/s at 802 m and 10−11 to 2 × 10−10 m/s at 1100 m) and very low porosity (~0.8% for the heterogenous sample and ~0.2% for the pure halite sample). Post-closure safety assessments based on numerical modeling provided bounding conditions around the thermal evolution of the disposal environment in crystalline rock for low heat generating ILW (50 W per 180-L vitrified waste canister), including exploring the sensitivity of temperature evolution within the borehole and rock environment to parameters such as heat load, borehole depth, geothermal gradients, and rock thermal conductivity. The coupling of heat transport with radionuclide migration to account for buoyancy-driven transport was shown to have a limited impact on radionuclide migration. For a disposal borehole in crystalline rock, the radionuclide concentrations and annual dose rates from key radionuclides (99Tc and 79Se) for a 500-m, 1000-m, or 3000-m deep borehole were negligible (i.e., many orders of magnitude smaller than the threshold dose the International Atomic Energy Agency considers insignificant for humans, 0.01 mSv/year). For disposal in rock salt, a suite of numerical model scenarios explored the effectiveness of the engineered barriers, including the glass matrix, primary package, and overpack, assuming diffusion-dominated transport. These scenarios illustrated that the performance of the disposal system was insensitive to the presence or absence of engineered barriers, as dose rates at late time (>105 years) were nearly identical for all scenarios. These results indicate that the natural barrier provided by the salt is very effective at containing radionuclides, while the engineered barriers serve mainly to delay the arrival of the peak dose. While the results are preliminary, the post-closure safety assessments, supported by measured data from crystalline rock and rock salt, give confidence that deep borehole disposal of long-lived ILW would result in dose rates considered insignificant for humans within a few meters from the borehole.

Numerical modelling of a high temperature borehole thermal energy storage system: Norway case study

Global warming is threatening life on earth. Utilising renewable energy is considered as the most effective measure to minimise anthropogenic CO2 emissions. High-temperature borehole thermal energy storage (BTES) systems have a world-wide potential to reduce energy consumption, increase energy utilisation of waste heat and provide efficient seasonal heat storage. Hybrid application of BTES and solar energy leads to net zero emissions. In this study HT-BTES is evaluated for seasonal thermal heat storage and recovery. To this end, a CMG STARS model was built and validated using the existing 100-wells BTES system in Norway. Then, the model was used to evaluate BTES thermal performance and thermal recovery efficiency. Sensitivity analysis was also conducted to study the dynamics of storage temperature in the BTES under different operating conditions, such as heat carrier flow rate, injection temperature, and charging period. Results of this case study show that the model-predicted temperatures during charging and discharging are in good agreement with the existing BTES system. In 5 years of operation, 35.5% of the heat injected into the BTES system was recovered, while the significant heat remained in the borehole region and lost to surrounding rock (64.5%). BTES was found very sensitive to flow rate, the charging period and injection temperature. Borehole depth has a minimal effect on BTES storage temperature at constant studied injection temperature.

Research on Sustainable Shallow Geothermal Potential in Jinan Start-Up Area, China

Shallow geothermal energy (SGE), as an important renewable energy, playing an important role in reducing carbon emissions. In order to efficiently and sustainably utilize SGE, field investigation and storage estimation are needed. In this study, the hydrogeological data obtained from the field exploration of Jinan Start-up Area were collected and compiled. By analyzing the geotechnical property data and thermal response test results, the information of geotechnical and thermal properties and underground temperature distribution characteristics were collected. Subsequently, the analytic hierarchy process (AHP) combined with the comprehensive index method (CIM) were used to classify the shallow geothermal potential of Jinan Start-up Area. The entire area was divided into a high-potential area, medium-potential area and general area, of which 92.2% was high-potential area. The preliminary results, combined with the parameters obtained from the testing, indicate that the SGE storage at a borehole depth of 120 m is estimated to be approximately 2.68 × 1012 kJ·K−1, while the heat exchanger power of the buried pipe at the same depth is calculated to be around 1.73 × 105 kW. Finally, suggestions are given for sustainable development and utilization of SGE in this area.

A novel study on influence of ground surface boundary conditions on thermal performance of vertical U-shaped ground heat exchanger

To better understand the influence of ground surface boundary conditions (GSBC) on the thermal performances of U-shaped ground heat exchangers (UGHE), this study proposes a numerical model with one energy balance boundary condition (EBBC) considering the spectrally selective properties of ground. This study comprehensively discusses the effects of operation and design parameters on the thermal responses of various GSBCs and UGHE. Additionally, the geographical performances of the EBBC are compared. The main results indicate that implementing EBBC in UGHE reduces prediction errors for water and borehole wall temperatures, with a maximum decrease of 1.70 °C and 1.78 °C, respectively. Regarding the average water temperature, the variation induced by different GSBCs can be reduced by 51.0% as the borehole depth increases from 50 to 125 m. Similarly, the difference induced by different GSBCs can be reduced by 22.7%, with ground thermal conductivity decreasing from 3.0 to 1.5 W/(m·K). Based on the geographical analysis, the convective GSBC can be imposed on UGHE for engineering approximation in only temperate and tropical regions. For other climate regions, the use of EBBC is recommended. Finally, the sensitivity analysis results indicate that borehole depth is the most important dependent variable, followed by ground conductivity and volumetric heat capacity.

Thermal Performance Analysis and Multi-Factor Optimization of Middle–Deep Coaxial Borehole Heat Exchanger System for Low-Carbon Building Heating

Ground-source heat pumps with deep borehole heat exchangers can fully utilize deep geothermal energy, effectively reducing the consumption of non-renewable energy for building air conditioning and achieving energy conservation and emissions reduction goals. However, the middle–deep coaxial borehole heat exchange (MDBHE) development is insufficient, and there is currently a lack of definitive guidelines for system optimal design and operation. This paper firstly establishes an effective and efficient system model and examines nine important parameters related to the design and operation of the MDBHE using a single-factor analysis. Thereafter, we compare and analyze the impact of different parameters through an orthogonal experimentation method. The findings reveal that the three most significant factors are borehole depth, inlet temperature, and mass flow rate, in descending order of importance. In addition, in terms of operation mode, this paper makes a comparative analysis of the operation of the MDBHE in variable flow mode and constant flow mode. The results showed that the average energy consumption of the pump in the variable flow mode decreased by 9.6%, and the surrounding ground temperature recovered at a faster rate.

Urban low-to-medium deep borehole field regeneration with waste heat from energy efficient buildings: A techno-economic study in Nordic climate

Due to large area requirement, ground-source heat pump (GSHP) systems with shallow boreholes are difficult to implement in dense urban areas. To address this limitation, alternative heat sources can be used to reduce heat extraction from ground or to inject regenerative heat to boreholes. This study investigates the techno-economic feasibility of utilizing two commonly available waste heat sources (waste air and wastewater) in urban environment. Passive and heat pump-assisted utilization are studied for apartment and office buildings, with varied borehole depth and two levels of urban density. Long-term GSHP system operation is simulated using iterative heat balance calculation and borehole dimensioning algorithms. The results show significant reduction in required borehole length with waste heat utilization, particularly in shallow borefields, with maximum reductions of 53.9% (apartment building) and 25.8% (office building). The studied waste heat sources are shown to enable a shallow borefield for otherwise insufficient borehole spacing, providing an alternative to deeper boreholes. However, waste heat only available during summer has limited impact on field sizing compared to a seasonally stable heat source. From an economic perspective, the levelized cost of heating could be reduced by 13.5% (apartment building) and 7.3% (office building) compared to baseline without waste heat utilization.

Drone Magnetic and Time Domain Electromagnetic Exploration in Metamorphic Formations: Tool for the Identification of Strategic Sites for Aquifer Exploitation

In the contemporary era, the exploitation of aquifers in the agricultural sector has become increasingly important. In response, researchers have directed their efforts towards the formulation of effective methodologies, with geophysical prospecting emerging as a fundamental tool in locating the best underground deposits. The magnetic prospecting technique can discriminate between different categories of rocks, which facilitates the localisation of geological contacts—an essential factor in determining the strategic location of boreholes, while electromagnetic time-domain prospecting helps in the definition of sedimentary strata. In particular, this process reveals the important influence of tertiary and metamorphic formations on the regional hydrogeological framework of the studied area. The variable yields recorded in the wells in the area that have yielded good results are a clear indication of the presence of aquifers. However, it is important to note that numerous wells have been drilled in this region that have yielded negligible or even zero flow rates. Prudent selection of the location and depth of boreholes is essential to ensure proper management of this resource. The use of drones equipped with magnetometers is essential to speed up the spatial mapping process. Empirical results corroborate the accurate classification of lithological units, thus facilitating the selection of sites for groundwater abstraction. These studies serve to validate initial hypotheses and profoundly enrich our understanding of the hydrogeological dynamics of the site, thus providing avenues for optimal and sustainable exploitation and future academic research.

Experimental and numerical investigations on operation characteristics of seasonal borehole underground thermal energy storage

To investigate operation characteristics of seasonal borehole underground thermal energy storage (SBUTES) with different operational strategies, a model test platform with reduced size was established based on similarity principle. The test results show that the larger the start-stop time ratio, the smaller the average heat exchange rate per unit depth (HERPUD) of borehole, and the lower the energy storage efficiency, but the thermal energy storage and extraction capacity increase. For the time ratio of thermal energy storage to extraction (TROSE), the larger the TROSE, the larger the thermal imbalance rate of energy storage body, which will lead to the gradual increase or decrease of temperature of energy storage body and is not conducive to the operation of energy storage. Compared with the asynchronous mode of storage and extraction, the synchronous mode of storage and extraction can effectively reduce the average temperature of energy storage body and increase the heat exchange efficiency of boreholes during the thermal energy storage. The focused energy storage mode can improve the energy storage efficiency and soil temperature recovery rate, balance the thermal energy storage and extraction capacity, and thus the performance of SBUTES can be optimized. A 3-D CFD model of borehole energy storage was established to further find the influences of borehole layout forms, layout spacing and depths on characteristics of the SBUTES. It can be found that for the energy storage efficiency, the hexagonal layout is the highest, the rectangular layout is the lowest, and the circular layout is slightly higher than the square one. Under the same volume of boreholes group, increasing the spacing of inner boreholes can effectively alleviate thermal interference of inner boreholes during the thermal energy storage, and the heat exchange capacity undertaken by inner boreholes can be improved. But it is not conducive to thermal energy extraction. Although increasing borehole depth can increase thermal energy storage and extraction capacity and system operation efficiency, the increase degree is decreasing with the increase of borehole depth, and the greater the borehole depth, the smaller the influence of borehole depth on characteristics of SBUTES.

Improved Analysis of Borehole Heat Exchanger Performance

This paper provides recommendations for improved analyses of the performance of ground-coupled heat pumps. Most research on ground-coupled heat pumps focuses on improving the performance of borehole heat exchangers (BHE) and reducing system costs. However, the potential improvements are mainly assessed at the BHE level rather than considering the entire system incorporating a heat pump, circulation pump, and building needs. This paper shows that such an approach can be misleading, and improvements in BHE are significantly overestimated if the operation of the entire system is not simulated. For instance, improvements in pipe thermal conductivity (from 0.4 to 3 W/(m K)) result in a 7.57% improvement in BHE performance when simulating only a BHE (constant inlet temperature assumed). However, a more realistic simulation of the entire system shows that improvements at a system level are only 0.15%. Other important simulation aspects are also investigated, focusing on different choices regarding the sensitivity analysis method, flow condition type, and optimization strategy. The results suggest that modifications to individual BHE parameters have a limited impact on the overall system performance, while modifying all parameters simultaneously can lead to more significant reductions in total system energy consumption (6% in this study). Furthermore, the research also shows that the potential savings in investment costs (by reducing the borehole depth) outweigh potential savings in operational costs.

Electromagnetic prediction of rock thermal properties beyond boreholes: Soultz-sous-Forets (France) case study

Estimation of deep temperature, thermo-hydro-dynamic and basin simulation, heat exchange and geothermal resource assessment require knowledge of the rock thermal properties beyond boreholes. At the absence of suitable methods and instruments for such estimates we propose a new approach to prediction of thermal conductivity, specific heat capacity and heat flow density based on results of electromagnetic sounding of the study area. Artificial neural network used to this end is taught by correspondence between laboratory measurements on cores from the drilled boreholes and adjacent electrical conductivity profiles determined by inversion of the electromagnetic sounding data collected in their vicinity. This approach is used to estimate rock thermal properties along NW-SE magnetotelluric profile crossing Soultz-sous-Forêts geothermal area, Alsace, France. We demonstrate that accuracy of such prediction both in depths below the boreholes and in the interwell space is comparable with that usually achievable in the borehole scale. In particular, it is shown that relative errors of thermal conductivity prediction at depths twice as large as the borehole depth are as small as 2%, and the accuracy of cross-well thermal conductivity prediction is 6% and 10% for dry and wet rocks, respectively. On the other hand, the prediction accuracy for matrix thermal conductivity of a rock from the known profile of dry thermal conductivity is about 8%. Based on the results of our studies, we constructed dry and wet thermal conductivity sections from the electrical conductivity model determined earlier by 2-D inversion of magnetotelluric data. The temperature model of the study area built along the same profile by means of electromagnetic geothermometer and the obtained thermal conductivity sections enabled estimating the profiles of the vertical component of heat flow density at the surface from dry and wet thermal conductivity sections. They could be considered as minimum and maximum constraints, respectively, bounding the area of its possible values, which, in turn, depend on in situ thermal conductivity of fluids filling the rock pores. The range of possible vertical heat flow density variations (100–150 ± 10% mW·m− 2) agrees well with heat flow estimates in the Upper Rhine graben and, in particular, in Soultz-sous-Forêts geothermal area roughly estimated earlier from borehole measurements. Using the artificial neural network trained on the correspondence between the specific heat capacity determined in the borehole and adjacent electrical conductivity profile, we built the model of specific heat capacity. Against the background, a zone of enhanced specific heat capacity ranging between 2.05 and 2.15 MJ·m− 3·K− 1 was observed in the domain located at the base of the sedimentary cover and upper part of the granitic basement.

Effects of site response on ground motion directionality based on KiK-net records and numerical analysis

The orientation variability of earthquake ground motions (i.e., GM directionality) is an important engineering characteristic in the seismic design of structures. The GM directionality is believed to be mainly related to source and site contributions. This paper investigated the effect of site response on the change of GM directionality from the borehole depth to the ground surface. Distribution of the range for orientation variability level at both borehole and surface was presented for different intensity measures of 3006 records from downhole arrays in the KiK-net database. It was observed that both the maximum direction orientation of intensity measures and the ratio at various orientations may change significantly from depth to surface, and it is dependent on the specific intensity measures and site class. The numerical analysis of soil column considering bi-directional shaking was demonstrated to have a good ability to capture the influence of site response on the GM directionality. Thereafter, some preliminary insights into the linear and nonlinear site response effects on the GM directionality were provided. The azimuthal variation associated with the predominant period of the input borehole motion is an important factor that results in the change of GM directionality at the surface.

Deployment of Geophysical Technique in Groundwater Search at Guinueaworm Endermic areas in Obubra local government area of cross river state, Nigeria

This study was conducted in the Guineaworm prone areas in Obubra Local Government Area, the study entails the deployment of vertical electrical sounding technique in the search for groundwater. In doing this, measurement was made in 14 profiles of 500m long each, using the IGIS resistivity meter model SSR-MP-ATS. Resist software was used for analysis. The Geoelectric sounding data interpretation revealed characteristic curves with two to six geoelectric layer thicknesses. The predominant curve types in the area were the KH, HKH, and HK. The electrical resistivity of the first layer ranged between 15.8to1626Ωm, which was indicative of clay, shale, or sandy silt, three to six geoelectric layers were obtained from the interpretation of the sounding data. The resistivity of the second layer ranged from 52.3 to 370.7Ωm. This was assumed to be shalestone/shale, and it was overlain by the third layer, which had resistivity values between 121 m to 1491.9Ωm, which was assumed to be sandstone (sandstone materials make good aquifers).The fourth layer, had values between 12.3Ωm. m to 1052.7Ωm, the fifth layer, had values between 11.21Ωm. to 2277.2Ωm, and the last layer, which had a value of32Ωm.The Transmissivity measurements ranged from 16 m2/day to 171 m2/day, Porosities were high with strong storactivity which show that the studied area contains thick and abundant aquiferous zone. Protective capacities (PC) values of (0.01-1.260 seimens) were obtained from the VES data. Borehole depths were recommended for each profile for borehole development. The study was identified to have confine aquifer terrain because of the confining clay layer which had a large vertical extend in the adjacent layers that enclosed the aquifer layer.

Data Mining Technology and Its Applications in Coal and Gas Outburst Prediction

Coal and gas outburst accidents seriously threaten mine production safety. To further improve the scientific accuracy of coal and gas outburst risk prediction, a system software (V1.2.0) was developed based on the C/S architecture, Visual Basic development language, and SQL Server 2000 database. The statistical process control (SPC) method and logistic regression analyses were used to assess and develop the critical value of outburst risk for a single index, such as the S value of drill cuttings and the K1 value of the desorption index. A multivariate information coupling analysis was performed to explore the interrelation of the outburst warning, and the prediction equation of the outburst risk was obtained on this basis. Finally, the SPC and logistic regression analysis methods were used for typical mines. The results showed that the SPC method accurately determined the sensitivity value of a single index for each borehole depth, and the accuracy of the logistic regression method was 94.7%. These methods are therefore useful for the timely detection of outburst hazards during the mining process.

Feasibility and investigation of residential HVAC system with combined ground source heat pump and solar thermal collectors in different climates of Iran

Geoexchange is one of the most energy-efficient, environmentally clean, and cost-effective space-conditioning systems available on the market. Seasonal storage of solar energy in geothermal boreholes is sharply interesting as a means of heating and cooling in buildings with different applications. In this study, a closed-loop geo-exchange and solar thermal system with two different heat exchangers are examined in an energy-efficient house. TRNSYS, a simulation software tool, was used to model the yearly performance of the hybrid ground-source heat pump (GSHP) system. Two different types of ground heat exchangers, e.g., tube-in-tube and U-tube were employed. The mass flow rate through the heat exchangers and the solar collector was examined to choose the best scenario for each of them. The economic benefits of a gray water heat recovery system and solar collector were studied; the results show that 517 and 536 US Dollars/Year can be saved from each of them, respectively. System performance analysis was carried out in different cities with various climates in Iran. Moreover, a complete economic assessment was evaluated for all cases. The results show that for the same inlet water temperature to GSHP, the tube-in-tube heat exchanger can pass 45% more flow than the U-tube heat exchanger for the same size as the HP. Furthermore, in the absence of the solar collector, a 2.7 × 108 kJ increase was conducted in the auxiliary heater component yearly. Finally, four different climates were evaluated for the launching of the GSHP system with a solar thermal collector. The hot and dry climate with 27 °C fluid inlet to a heat pump, a total borehole depth of 220 m, and an initial cost of $ 25,047 was selected as the most appropriate weather conditions for launching the system in Iran.

Monitoring of methane in groundwater from the Vale of Pickering, UK: Temporal variability and source discrimination

Groundwater abstracted from aquifers in the Vale of Pickering, North Yorkshire, UK and monitored over the period 2015–2022, shows evidence of variable but commonly high concentrations of dissolved CH4. Sampled groundwater from the Jurassic organic-rich Kimmeridge Clay Formation (boreholes up to 180 m depth) has concentrations up to 57 mg/L, and concentrations up to 59 mg/L are found in groundwater from underlying confined Corallian Group limestone (borehole depths 50–227 m). The high concentrations are mainly from boreholes in the central parts of the vale. Small concentrations of ethane (C2H6, up to 800 μg/L) have been found in the Kimmeridge Clay and confined Corallian groundwaters, and of propane (C3H8, up to 160 μg/L) in deeper boreholes (110–180 m) from these formations. The concentrations are typically higher in groundwater from the deeper boreholes and vary with hydrostatic pressure, reflecting the pressure control on CH4 solubility. The occurrences contrast with groundwater from shallow Quaternary superficial deposits which have low CH4 concentrations (up to 0.39 mg/L), and with the unconfined and semi-confined sections of the Corallian aquifer (up to 0.7 mg/L) around the margins of the vale. Groundwater from the Quaternary, Kimmeridge Clay formations and to a small extent the confined Corallian aquifer, supports local private-water supplies, that from the peripheral unconfined sections of Corallian also supports public supply for towns and villages across the region.Dissolved methane/ethane (C1/C2) ratios and stable-isotopic compositions (δ13C-CH4, δ2H-CH4 and δ13C-CO2) suggest that the high-CH4 groundwater from both the Kimmeridge Clay and confined Corallian formations derives overwhelmingly from biogenic reactions, the methanogenesis pathway by CO2 reduction. A small minority of groundwater samples shows a more enriched δ13C-CH4 composition (−50 to −44 ‰) which has been interpreted as due to anaerobic or aerobic methylotrophic oxidation in situ or post-sampling oxidation, rather than derivation by a thermogenic route.Few of the existing groundwater sites are proximal to abandoned or disused conventional hydrocarbon wells that exist in the region, and little evidence has been found for an influence on groundwater dissolved gases from these sites. The Vale of Pickering has also been under recent consideration for development of an unconventional hydrocarbon (shale-gas) resource. In this context, the monitoring of dissolved gases has been an important step in establishing the high-CH4 baseline of groundwaters from Jurassic deposits in the region and in apportioning their sources and mechanisms of genesis.

Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway

In order to solve the support problem of deep soft crushed coal roadway, a concentrated cavern in a mining station of a mine is taken as the test object. Based on the analysis and summary of the field observation data and the law of rock pressure appearance, a new technology of pressure relief anchoring with the main body of “initiative support + borehole pressure relief” is proposed. This new technology will carry out strong active support in the shallow part of the surrounding rock and excavate a row of low-density large-diameter pressure relief boreholes in the deep coal body of the roadway ribs. The numerical analysis model is established by FLAC3D, and the second invariant of deviatoric stress (J2) is used as the analysis index to elaborate the influence of different borehole parameters on the pressure relief effect of roadway surrounding rock. The results show that different borehole parameters have different effects on roadway pressure relief, that is, borehole depth > borehole length > borehole spacing. After the borehole process is used to relieve the pressure of the surrounding rock, the deformation of the mining roadway side in the subsequent observation process is always controlled within the range of 100 mm, and the shallow surrounding rock support system is effectively protected. The comprehensive control effect is very obvious. Therefore, the field practice proves that the supporting technology can effectively solve the problem of large deformation support of similar roadway surrounding rock.

Study on effects of multi-climatic parameters on performance of ground source heat pump through coaxial borehole heat exchanger

ABSTRACT The accurate calculation for heat flux of borehole heat exchanger (BHE) is of great importance for design of ground source heat pump (GSHP); the climatic conditions influence GSHP performance through GHE. In this study, a 2-D heat transfer model for coaxial BHE was built to investigate the effects of multi-climatic parameters on BHE heat transfer and GSHP performance. The outlet temperature, ground temperature profiles and COP of GSHP system for the cooling period were concerned. The effects of climatic conditions under different borehole depths, ground thermal conductivities and flow rates were studied. The studies showed that the outlet temperature from BHE increased about 10% and system COP declined about 5% in cooling mode with considering the effect of climatic conditions. The comparison indicates that the effects of climatic conditions on coaxial BHE are stronger than that on U-tube BHE. Generally, the climatic conditions influence BHE heat transfer mainly through the shallow ground and the influences strengthen with time. The effects can be more significant with a larger ground thermal conductivity, but it weaken with increase of borehole depth. Also, the effects of climatic conditions on BHE and GSHP seem to be independent of flow rate.