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Energy Exploration & Exploitation
Journal Prestige (SJR): 0.501

Citation Impact (citeScore): 1
Number of Followers: 4

This is an Open Access Journal

Open Access journal
ISSN (Print) 0144-5987 - ISSN (Online) 2048-4054
Published by Sage Publications

[1174 journals]

Numerical simulation and sensitivity analysis of automatic optimization of
gas extraction well locations in abandoned mines
- Authors: Guiqiang Zheng, Tianxin Gao, Dong Chen, Dequan Liu, Yongjian Wang, Dongxin Guo, Fengyu Liu, Mengya Fan
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  There are large numbers of abandoned mines in China and abroad, among of which stores relative abundant coal-bed gas. The gas extraction from abandoned mines can be used for power generation or industrial gas utilization. In this paper, the present situation of abandoned mines in China and abroad was studied, and the disadvantages of the common layout and optimization methods of gas extraction in abandoned mines were pointed out. Based on the analysing of reservoir conditions and physical property parameters, the finite element software COMSOL was used to do the numerical simulation of extraction well automatically optimize, and take shenbei coal mine as an example. Moreover, an automatic optimization APP of well location was developed based on the results of simulation. Finally, the parameter sensitivity of gas extraction is analysed. Through the study, it is found that the most basic and common method of gas extraction in abandoned mines is empirical method, which lacks of theoretic support and accuracy, thus causing unreasonable extraction and waste of resources. In this study, the COMSOL numerical simulation software was used to explore the numerical simulation method of automatic well position optimization combined with the optimization algorithm. The Nelder-Mead algorithm was selected as the optimization algorithm after comparing the advantages and disadvantages of various algorithms. The operation flow and type of Nelder-Mead algorithm were analysed, and the optimization parameters of numerical simulation were set. Through the numerical simulation, the function of automatically searching the high-gas production position near the preset well position was realized, and the automatic optimization APP for gas extraction in abandoned mines was developed. Finally, the sensitivity of parameters to gas production in different well locations under three different pumping conditions which are horizontal, vertical and bottom-hole negative pressure was analysed; and the simulation results were discussed.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-06-17T06:00:26Z
  DOI: 10.1177/01445987221099084
Desensitization effect of chemically induced coal components at room
temperature: An experimental study
- Authors: Lv Xiangfeng, Ji Xuan, Chen Fan, Lin Xin, Meng Lingfeng, Yang Yahan
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  This study was conducted to address the rock burst problem caused by serious stress concentrations in coal seams. Based on the principle of inducing agent corrosion affecting coal components to soften coal, different inducers were selected to study the desensitization effect of acid leaching induction on coal components. The microscopic behavior characteristics of coal under acid leaching were analyzed, and the qualitative and quantitative laws were obtained for different acid leaching times and microscopic behavior characteristics. The results show the following: (1) The mixed acid solution as an inducer has the effect of immersion, dissolution, and fracture on coal. During the reaction process, the internal pores of the coal expand, and the height of the external liquid decreases. The mixed acid solution had the best effect in terms of the removal of minerals in coal. (2) Under microscopic conditions, the internal crack width of the coal body expanded several times after mixed acid soaking; the difference in the unevenness before and after compression fracture was stable at 25–27%, and the mixed acid expanded the gap in the coal. (3) This practical study shows that the characterization changes of the mixed acid solution, injected into the borehole, combines the characteristics of the citric acid and phosphoric acid solution. The minerals around the borehole are dissolved, and the debris fuses with the solution. The liquid is viscous and forms a film on the surface of the solution. The mixed acid has a more obvious effect on the immersion and dissolution of coal.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-06-09T01:20:50Z
  DOI: 10.1177/01445987221098220
Integrated energy planning and modeling (IEPM) for sustainable electricity
generation in Pakistan: Challenges and limitations
- Authors: Sana Bashir, Sumaira Kanwal, Hassan Zeb, Zaeem Bin Baber, Asma Majeed
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Recent technological advancements demand IEPM for sustainable energy development through the induction of advanced computational techniques. However, the applicability and outcomes of such modeling tools vary due to underlying limitations in addition to gaps within the energy sector. This study uses a three-pronged approach to determine the potential of IEPM in shaping sustainable energy systems, particularly for Pakistan. Findings suggest that the main hindrances in sustainable electricity generation in Pakistan are over dependence upon thermal fuel mix and partial achievement of national energy policy targets. A review of the public sector plans, researches, and historical energy mix of Pakistan affirms that all efforts are targeted towards least cost electricity production without considering social and environmental impacts. All past studies projected energy supply and demand to ascertain future implications, but no one suggested sustainable alternatives for meeting national energy targets. Findings of this study necessitate upon development of a fair, consistent, long-term and sustainable IEP with clear policies to overcome sectoral bottlenecks and attain a high growth trajectory. A review of modeling tools, their applications and limitations, carried out in this study, suggests the adoption of the LEAP model for realistic IEP for Pakistan. This considered LEAP’s strengths in terms of energy-environment nexus, strong-accounting and scenario-building, bottom-up/top-down approach, user-friendliness, and spatial-temporal flexibility.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-06-08T04:30:18Z
  DOI: 10.1177/01445987221105098
Experimental investigation on mechanical properties of coal samples under
different freeze–thaw cycles
- Authors: Chengyong Zhou, Yugui Yang, Shanshan Hou, Chengzheng Cai, Fulin Li, Cheng Xu
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Due to the extensive excavation of open-pit coal mines in northwest of China, the rock slopes formed by special environments are subjected to freeze-thaw (F-T) action, which has a certain impact on their stabilities. In order to evaluate the mechanical properties and micro damage characteristics of coal under different freeze-thaw cycles, uniaxial compression experiments combining acoustic emission tests were conducted. The results suggest that as the number of freeze-thaw cycles increased, elastic modulus of coal samples decreased, the samples showed ductile damage characteristics and initial compaction stage gradually increased. Compared with unfrozen-thawed coal sample, the compressive strength of the coal samples decreased by 23.27% after 10 F-T cycles, 31.06% after 15 F-T cycles, and 36.01% after 20 F-T cycles. The internal fissures in the coal samples transitioned from tensile fissures to shearing fissures, and the samples gradually showed tensile-shear combined failure. The final cumulative energy of the coal sample became lower, the cumulative energy duration increased and the time point of the energy surge was delayed with the increase of cyclic freeze-thaw times. A damage model based on the evolution law of the cumulative energy was established to bridge the gap between macro-micro damage mechanics.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-06-07T05:18:00Z
  DOI: 10.1177/01445987221106567
Standalone photovoltaic and battery microgrid design for rural areas
- Authors: Cyprien NSENGIMANA, Liu Kai, Cao Yuhao, Lingling Li
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The remote location and many islands in Africa are experiencing a big power shortage and blackouts and they greatly necessitate electric power from standalone photovoltaic microgrid. In Rwanda, off-grid solar systems are at their infancy level and their affordability for the rural population requires thorough support and incentives. In this process, the Government of Rwanda (GoR) has set a program to subsidize the cost of the system in a rural household power access projects suit to their socio-economic metric known as ‘Ubudehe’ which would determine the required financial support from other poverty reduction programs in a country. The design of a standalone photovoltaic microgrid is aimed to find the cheapest way to go for either a single rural house or a group of 200 rural houses with similar load demand as a long-term solution to their local energy challenges. The models resulted in a Levelized cost of energy, least cost of energy (LCOE) of 1.51US$/kWh for a single home while the LCOE for the group of houses load equals 1.45US$/kWh. The net present cost (NPC) for a single home and multi-user load are respectively equal to 5,625US$ and 1,079,210US$. These results conclude the efficacy of the group sharing load demand model design to provide green energy solutions to the mid-and low-income rural population in Rwanda.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-30T06:17:24Z
  DOI: 10.1177/01445987221102196
Environmental risk assessment of inter-well partitioning tracer compounds
shortlisted for the offshore oil and gas industry
- Authors: Mehul Vora, John-Sigvard Gamlem Njau, Steinar Sanni, Roger Flage
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Quantifying residual oil saturation (SOR) in the inter-well region of oil and gas reservoirs is key for successfully implementing EOR solutions. Partitioning inter-well tracer tests (PITTs) has become a common method for quantifying SOR. A new group of seven chemicals – pyridine, 2,3-dimethyl pyrazine, 2,6-dimethyl pyrazine, 4-methoxybenzyl alcohol, 3,4-dimethoxybenzyl alcohol, 4-chlorobenzyl alcohol, and 2,6-dichlorobenzyl alcohol – have been proposed as potential partitioning tracers for quantifying SOR. Using these tracers can lead to their environmental release in the marine environment through produced water discharges, with currently limited knowledge on impacts in the marine ecosystem. The primary objective of the present study is to assess the environmental risk of discharging the tracer compounds in the marine environment. We investigated the fate and effect of these tracers in the marine environment. Biodegradability in seawater was measured to understand the fate of tracers in the marine environment. The acute toxicity of tracers was measured in terms of the percent cell viability of a rainbow trout gill cell line (RTgill-W1) and growth inhibition of the algae Skeletonema costatum. The ecotoxicological information obtained from these experiments was used in the dynamic risk and effects assessment model (DREAM) to calculate the tracers’ contribution to the environmental impact factor (EIF). The results from the DREAM simulations suggest no contribution towards EIF values from any of the tracers at the expected back-produced concentrations. Results from simulations at higher concentrations suggest that both pyrazines have the lowest environmental risk, followed by 3,4-dimethoxybenzyl alcohol, 4-methoxybenzyl alcohol, and pyridine; while both chlorobenzyl alcohols show the highest environmental risk.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-25T06:55:09Z
  DOI: 10.1177/01445987221097999
Productivity prediction with consideration of stress-sensitive
permeability in naturally fractured carbonate reservoir
- Authors: Congge He, Lun Zhao, Heng Song, Zifei Fan, Anzhu Xu, Xing Zeng, Haiyan Zhao, Qingying Hou, Yefei Chen, Jincai Wang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The aim of this paper is to illustrate the impact of stress-sensitive permeability on productivity in naturally fracture carbonate reservoirs. First, stress sensitivity evaluation experiments were conducted on artificial cores with matrix, uncemented fracture, partially- cemented fracture and fully-cemented fracture by measuring their permeability in the process of increasing confining pressure. Then, a new mathematical model for productivity prediction in naturally fractured carbonate reservoir with consideration of stress-sensitive permeability is developed. Comparisons have been made between the new model prediction results and field measured data to verify the accuracy of the new model. Finally, based on the validated model, the detailed impact of permeability modulus on productivity is analysed. The experiment results show that the strength of stress sensitivity, evaluated by permeability modulus, of cores with uncemented fracture and partially-cemented fracture is generally an order of magnitude larger than that of cores with matrix and fully-cemented fracture. The results show the new model can be simplified to the classic model (Vogel equation) under the condition of the stress sensitivity being not taken into account, which means the class model is corresponding to a special case of this new model. Field application shows that the new model is reliable and correct. Moreover, with the help of the new model, it is found that the impact of stress-sensitive permeability on productivity increases with increasing permeability modulus and decreasing flow bottom hole pressure.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-24T02:50:46Z
  DOI: 10.1177/01445987211064675
Exploring weathered and oxidized zones of coal seams using the transient
electromagnetic method
- Authors: Yang Yang, Bin Xiong, Sanxi Peng, Siqin Liu, Hanbo Chen, Tianyu Zhang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Once a coal seam has been weathered and oxidized, the quality of the coal is lost and the coal resources are wasted. At the same time, new risks are introduced to the safe operation of the coal mine. Therefore, it is critical to determine the extent of the weathered and oxidized zone in the coal seam. This paper depicts the electromagnetic characteristics of the weathered and oxidized zone of coal seams, briefly introduces the method of detection by transient electromagnetic method (TEM) and the data processing steps, and performs the numerical simulation for the simplified resistivity model of weathered and oxidized zone in a coal seam. It is observed that after the coal seam has been weathered and oxidized, the electromagnetic characteristics (secondary field potential and resistivity) will be dramatically affected, namely high secondary field potential and low resistivity. For experimental verification purposes, this study selects the test project of the Shixin Minefield in Shanxi, China as an example, and the accuracy for the detection of the weathered and oxidized zone of the coal seam using TEM is successfully verified.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-23T05:31:35Z
  DOI: 10.1177/01445987221102982
Hourly comparative assessment of photovoltaic thermal collector subjected
to nanofluid for complete year: A case study of major cities in Pakistan
- Authors: Batoor Khan, Nadeem Ahmed Sheikh, Iván. E. Castañeda-Robles, Luis. D. López-León, Rasikh Tariq
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  This research targets to present a case study on the annual comparative assessment of photovoltaic thermal collectors (PV/T) by using water and Ag/water nanofluid for five different cities in Pakistan. The assessment is conducted at monthly, daily, and hourly resolutions. PV/T collector is imitated through a set of energy balance based physical models which are solved numerically for two working fluids (i.e. water and Ag/water nanofluid) in a yearly simulation format (with hourly, daily, and monthly predictions) for five major cities of Pakistan (Taxila, Peshawar, Multan, Lahore, and Karachi). Detailed comparative assessment is carried out based on the performance indicators such as electrical efficiency, thermal efficiency, heat gain, and net electricity power generation. In the results section, hourly, daily, and monthly patterns of performance indicators using water and Ag/water nanofluid are reported, followed by a comparative study between the different cities having different climatic conditions. The sensitivity of nanofluid's mass flow rate and its particle concentration on the performance indicators is also reported, and the analysis of the sensitivity of the nanofluid characteristics on the pumping and the net useful power is also presented. Assessment has indicated that the overall efficiency for Taxila, Peshawar, Multan, Lahore, and Karachi cities are similar and around 66% despite having different latitude and longitudinal locations. While using silver nanofluid as a working fluid, compared to the usage of pure water as a working fluid, overall lesser efficiency is seen at around 63.80%, for selected cities.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-20T08:15:22Z
  DOI: 10.1177/01445987221099957
Evaluation of coalbed methane resources in Xinjing Baoan block based on
PCA, TOPSIS, & MLFM
- Authors: Fengjie Chen, Xiuming Jiang, Caifang Wu, He zhou, Bin Gao, Shasha Zhang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Coalbed methane (CBM) resources are abundant in the Baoan blocks of the Xinjing coalfield, China; their exploration and development remain in infancy. Suitable development blocks can be selected by evaluating their development potential; that of the No. 8 and 15 CBM systems in the Baoan blocks was evaluated using three quantitative evaluation methods via existing geological data: multi-level fuzzy mathematics (MLFM), technique for order preference by similarity to ideal solution (TOPSIS), and principal component analysis (PCA). The results demonstrated that the CBM development potential in the central part of the Baoan blocks is low and unbecoming. The favorable areas of the No. 8 coal seam are distributed in the northeast and northwest, and that of No. 15 in the northwest and southwest Differences exist in quantitative selection; with limited data, the evaluation of the TOPSIS method is considerably different from actuality, and is unbecoming for evaluating the development potential.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-16T02:13:21Z
  DOI: 10.1177/01445987221096750
Pore characteristics and its heterogeneity of lignite reservoir in the
Erlian Basin of Inner Mongolia, China
- Authors: Pengfei Jiang, Hao Xu, Heng Wu, Fudong Xin, Tiantian Zhao, Xiangyang Chen
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The pore characteristics of coal reservoirs play a very important role in the migration of coalbed methane reservoirs, and its heterogeneity has been studied by a large number of scholars. However, there are few studies on lignite reservoirs. In this paper, three sets of lignite reservoirs in the Jiergalangtu depression are taken as the research object. The scanning electron microscope (SEM) images are converted from time-domain signals to frequency-domain signals through Fourier transformation, which quantitatively characterizes the heterogeneity of coal reservoirs. The variance of the value indicates that the three sets of coal seams NO.4Var
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-10T06:20:05Z
  DOI: 10.1177/01445987221099088
Influencing factors and experimental study on electrothermal high
temperature field of the outburst coal in China
- Authors: Jin Yang, Xionggang Xie, Jianing Luo, Zhifei Liu, Jianjun Ren
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  In this study, we proposed a method to solve the problems of low permeability of the outburst coal seams and gas extraction in China. We used heating cables to heat outburst coal seams and increase the gas desorption capacity of coal seams to prevent outbursts. An experimental cement tank was constructed to investigate the influence of the heating temperature, cable layout and thermal insulation conditions in the cement tank on the electrothermal high-temperature field characteristics of the outburst coal sample. The following results were obtained: The effective heating radius of the heating cable was 800 mm ≤ R
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-09T11:09:06Z
  DOI: 10.1177/01445987221095186
Evolution of mining stress field and the control technology of stress
relief gas in close distance coal seam
- Authors: Hui Cheng, Hongbao Zhao, Dongliang Ji, Luyang Cui
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The prevention and control of stress relief gas have crucial influence on safety of coal mine, it is not only the inevitable requirement of safe production, but also an effective way to realize reasonable utilization of gas. Taking the 1103 working face of the Weijiadi coal mine as the background, the mining stress field was analysed by means of numerical simulation, theoretical analysis and field practice, and the control technology of stress relief gas was studied. The results showed that scope of stress relief zone drops gradually associated with an increase of distance from the roof (or floor) to the working face. Additionally, the shape of the stress relief body exhibited a ring-shaped distribution, while four corners of the goaf roof and floor underwent high permeability zones due to a deep stress relief body, where the permeability of two corners near the transportation roadway of the floor was higher. The results provided good information for W-shaped ventilation mode with two inlets and one return which was adopted in the working face. More importantly, the optimized layout of boreholes was put forward, which eventually were useful for solving the gas overrun of the working face. The technology used in 1103 working face has an attractive and practical background with other extensive applications for the prevention and control of relief gas.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-06T11:17:06Z
  DOI: 10.1177/01445987221099608
Experimental study on indoor environmental factors of double film solar
greenhouse and traditional Chinese greenhouse in cold region
- Authors: Yerui Liu, Xiaomin Liu, Yune Chai, Linyan Yang, Wei Wei, Jinshou Gu, Hong Kang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  In order to create a suitable thermal and humidity environment for crop growth in the solar greenhouse, a novel polystyrene foam modular double film solar greenhouse was designed and constructed. The double film solar greenhouse wall adopted polystyrene foam modules, with internal and external supporting frameworks and covering double-layer film, forming a thermal buffer zone which can collect and store solar energy passively. We tested indoor environmental factors variation of the double film solar greenhouse and the ordinary single film greenhouse in winter. Compared with the single film solar greenhouse, results show that the double film solar greenhouse effectively improves the indoor air, soil temperature and CO2 concentration, and reduces the indoor air humidity and soil humidity. The value of environmental factors of light, heat, water and air system in double film greenhouse is more stable than that in single film ordinary greenhouse. It provides a theoretical basis for the construction of double film solar greenhouse and indoor environment regulation.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-06T11:16:56Z
  DOI: 10.1177/01445987221098099
Extremum seeking control of PV system based on least- squares approach
(real-time optimization)
- Authors: Rabiaa Gammoudi, Houda Brahmi, Rachid Dhifaoui
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Today renewable energy has become an absolute necessity taking into account the price of fossil energies and the pollution resulting from her large exploitation. Solar radiation can be converted directly into electrical energy, in the form of direct current, by means of a solar cell. Finding the maximum power point is an essential part in photovoltaic systems. Indeed, the output power varies greatly depending on illumination, temperature, but also the overall aging of the system. In order to operate a PV generator as often as possible at its optimum power, we must introduce a controller and a static converter which will act as an adapter between the source and the load. Many works review the different maximum power methods to adjust the optimal output power and improve the efficiency of the PV system. These methods are broadly classified into several categories. In this paper, such an experimental regulator based on a power mathematical technique is proposed, which is founded on least squares method to estimate the maximum power when operating sub-optimally. This technique makes it possible to compare experimental data, generally tainted with measurement errors, with a mathematical model supposed to write these data. This study gives the opportunity to experimentally test a mathematical method with a PV system which mainly uses a BOOST chopper. The DC / DC converter and the regulator are designed and produced within the research unit while using an STM32F4 microcontroller over sun. The results obtained from the use of this optimization technique clearly show the very high fidelity between the real values of the current and voltage and their optimal estimated values with a certain uncertainty which does not exceed almost 2%, which shows a good agreement. In the same way, this approach makes it possible to minimize the oscillations around the MPP, which already makes it possible to improve the efficiency of the system which is very close to 100% in experimental tests.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-05-03T11:26:02Z
  DOI: 10.1177/01445987221095590
Research and application of Gob-Side entry retaining with roof
presplitting under residual coal pillar of upper coal seam
- Authors: Xichun Tian, Jiong Wang, Guangyuan Yu, Haoseng Wang, Peng Liu, Zhifu Pan, Yanjun Wang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  In the mining of close coal seam, the stress concentration under the residual coal pillar in the upper coal seam leads to serious deformation to roadway surrounding rock in the lower coal seam. Hence, it poses a huge challenge to the maintenance of entry surrounding rock. Based on this, an approach of entry surrounding rock control technology, directional pre-splitting, and roof-cutting pressure relief, was applied. The stress and deformation of entry surrounding rock utilizing directional pre-splitting and roof-cutting pressure relief were studied by numerical simulation and field test The results indicated that the depth of stress concentration under the residual coal pillar achieve 44 m. With the application of the roof presplitting, the vertical stress of the entry roof decreased. Utilizing the roof presplitting with a height of 7 m and an angle of 15°, the gangue filled the goaf and supported the overlying strata. Meanwhile, the surrounding rock of entry was controlled with a constant resistance anchor cable (9 m length) and gangue prevention support structure. Through field test monitoring, the roof pressure and the deformation of surrounding rock increases rapidly at 30 ∼ 110 m behind the working face. From 110 ∼ 160 m, the increased rate of roof pressure and surrounding rock deformation gradually slows down and tends to be stable at 160 m behind the working face. The maximum displacement of the roof to the floor is 511 mm, and the maximum displacement of the gangue rock wall to coal wall is 421 mm. The remaining roadway meets the demand of the adjacent working face.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-04-27T07:49:11Z
  DOI: 10.1177/01445987221095116
Study on mechanism and improvement technology of Top coal loss in
horizontal sublevel fully mechanized caving mining
- Authors: Fengfeng Wu, Shurong Zhang, Xin Yue, Changyou Liu, Qiwen Liu, Jian Zhang, Bo Lv, Zhiqiang Gao
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  In view of solving the problems of large top coal loss and low recovery rate in the traditional caving process of horizontal section fully mechanized caving mining, taking the fully mechanized caving face of steeply inclined and extra-thick coal seam in Yimen Coal Mine as the engineering background and the research method of numerical simulation and field measurement was used to study the coal gangue flow characteristics under different coal caving directions and different number of coal caving ports at the bottom plate side, revealing the mechanism of top coal loss and proposing the technology to improve the recovery rate. The results show that the action time of top gangue and the ‘ rotation ‘ of coal gangue flow in the triangle coal area jointly promote the release of triangle coal in the bottom plate, which makes the coal gangue interface steeper and the release rate higher when the coal is released in the lateral direction of the bottom plate; adjusting the number of opening coal mouths when the initial coal caving at the floor side can coordinate the top coal caving speed, gangue down-channeling speed and the closing time of the coal caving mouth. When the first coal caving opens two coal caving mouths, the recovery rate of bottom triangular coal is the highest. Yimen Coal Mine adopted the floor lateral roof side caving and double-mouth caving technology. Compared with the original scheme, the top coal recovery rate of the working face increased by 3%, and the top coal recovery rate of the floor triangle area increased by 7%.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-04-08T05:46:44Z
  DOI: 10.1177/01445987221092850
Temporal variation of hydrogeochemical characteristics and processes of
aquifers in the Liuqiao coal mine
- Authors: Guangtao Wang, Jiwen Wu, Xiaorong Zhai, Hongmei Zhang, Yaoshan Bi
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Studying the characteristics and hydrogeochemical evolution processes of groundwater can contribute to the prevention of water-related hazards and ensure sustainable management of groundwater resources. In this study, the hydrogeochemical characteristics and evolution processes of the coal-bearing sandstone aquifer and Carboniferous limestone aquifer of the Taiyuan formation in the Liuqiao coal mine in Huaibei coalfield were assessed using piper diagram, Gibbs diagrams, ionic proportion ratios, and principal component analysis (PCA). The results showed that Na+ + K+ and SO42− were the dominant cations and anion, respectively, in both aquifers. The coefficients of variation of six hydrochemical parameters increased gradually, reflecting the formation of different water chemical compositions. The formation of hydrochemical compositions was dominated by water-rock interaction, including the dissolution of rock salt, cation exchange adsorption and pyrite oxidation. In addition, the PCA revealed two first components, explaining the highest proportion of variance. Over time, the water sample points were mostly found in the second and third quadrants, indicating the groundwater salinization effect as a result of the gradual increase in the cation alternating adsorption.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-21T08:10:05Z
  DOI: 10.1177/01445987221088621
Massive dolomitization driven by MgSO4-rich seawater and its effects on
thermochemical sulfate reduction, Upper Permian Changxing Formation,
northeastern Sichuan, China
- Authors: Kaikai Li, Chunfang Cai, Xianfeng Tan, Hua Jiang, Junjia Fan
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Massive dolostones replacing build-ups and containing H2S of thermochemical sulfate reduction (TSR) origin occur in the Upper Permian reef and bank deposits, northeastern Sichuan, China, despite the absence of gypsum or anhydrite deposits, which are usually present in TSR cases. Fluid chemistry from fluid incluions and δ13C, δ18O and 87Sr/86Sr values from different diagenetic phases were measured to determine the dolomitization regime, and to assess the relationships between the occurrence of dolomitization and H2S accumulation. Dolomitization was initiated by seawater with slightly increased salinities (penesaline) at shallow depths prior to chemical compaction. The micro- to fine-crystalline cloudy dolomite formed with relatively high Na and Sr contents, and with δ13C, δ18O and 87Sr/86Sr values (2.2‰∼4.8‰, −3.9‰∼-5.0‰ and 0.70724∼0.70746, respectively) inherited from seawater. The evaporation of Permian seawater in back-reef and inter-reef lagoons during sea-level fall and the subsequent seepage reflux into reef-beach bodies led to greater Mg2+ and SO42− concentrations in higher-salinity pore waters. Further massive dolomitization was promoted by compactional flow of hotter residual seawater at shallow to intermediate depths and resulted in the formation of fine- to medium-crystalline clean dolomite with lower Na and Sr contents, more depleted δ18O values (-5.1‰∼-6.0 ‰), andδ13C (2.5‰∼4.8 ‰) and 87Sr/86Sr values (0.70726∼0.70741) similar to those of the coeval seawater. The relatively closed hydrodynamic system during burial facilitated SO42− preservation. The whole dolomitization process enriched porewater SO42−, which have been almost exhausted by subsequent TSR, accounting for the high present-day concentrations of H2S. The output of this study shows that similar scenarios involving dolomitization driven by condensed MgSO4 seawater and H2S accumulations can occur in evaporite-free settings across a broad range and deserves special attention during deep oil/gas exploitation.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-16T08:34:41Z
  DOI: 10.1177/01445987221083758
Research on multi-parameter inversion of the phenomenon of gob breathing
induced by atmospheric pressure fluctuation
- Authors: Bing Wu, Binbin He, Chenguang Zhao, Baiwei Lei
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  It is significant to predict the gas emission in the mine gob accurately for gas drainage to prevent accidents and ensure safe production. The change of atmospheric pressure makes the gas emission in the mine gob presents a “breathing phenomenon”, which causes the gas concentration in the return airway of the working face fluctuates even if there are no other disturbances. The gas emission of the return airway in mine working face is affected by many factors, so it is difficult to analyze the influences of atmospheric pressure fluctuations on the gas emission of mine gob. In order to reduce interference factors, by continuously monitoring the gas concentration in the return airway of a does not work mine, in the meantime, simultaneously monitoring and analyzing the atmospheric pressure on the ground, this paper studies the influence rules of atmospheric pressure on gas emission in goaf. And a new multi-parameter mathematical model for gas emission in gob is developed, the Particle Swarm Optimization algorithm (PSO) is used to invert the optimal parameters, and the model is verified by random monitoring data. The results show that the model can accurately indicate the influence of atmospheric pressure on gas emission in the gob. The faster the ground atmospheric pressure decreases, the higher the gas emission rate of the gob is, and the faster the ground atmospheric pressure increases, the lower the gas emission rate is. In addition, the mathematical model can also invert the effective permeability and effective porosity of the gob, which provides a new idea for the prediction of gas emission from goaf and the evolution characteristics of permeability in goaf.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-15T08:35:34Z
  DOI: 10.1177/01445987221087496
Study on the coupling migration law of airflow-respiratory dust of an 8-m
high fully-mechanized mining face
- Authors: Fang Chen, Jinming Mo, Wei Ma
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  8-m super-high fully mechanized mining face has been successfully applied in China, which has brought many difficulties to dust control. The main reason is that the mining height increases and the dust distribution and evolution law are quite different. Targeting the 12,513 fully-mechanized mining face in Bulianta Coal Mine of China in this paper. The spatial evolution of airflow-respiratory dust of an 8-m high fully-mechanized mining face is analyzed using numerical simulation and underground measurement methods. The results reveal that the numerical and measured results are consistent. At the working range from 15 m in front of the shearer to 30 m behind it, the wind speed increases with an average rise of 70% on the coal cutting side. The airflow diffusion at the working face is primarily longitudinal and partly transverse. Along the airflow direction, the respiratory dust concentration in the pedestrian space first increases and decreases, followed by a marginal increase and gradual decrease，and the dust concentration increased with the increase of height, the migration distance of dust particles was directly proportional to time, and the smaller dust particles were prone to transverse diffusion. In the range of 20–30 m from the downwind side of the shearer, the transverse diffusion of coal cutting dust and the dust produced by support coal falling show conversion, leading to the increase of dust concentration. Under the same dust production intensity, compared with ordinary mining height, with the increase of mining height, the influence range of dust diffusion is wider, the floating duration is longer, and the space dust concentration will be reduced, and the support coal falling dust is the main dust pollution source in pedestrian space. The results reveal that the numerical and measured results are consistent, and obtained the relationship of spatial evolutions of respiratory dust
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-11T02:14:43Z
  DOI: 10.1177/01445987221086021
Practical Application of Oxygen Augmentation Observation in the Process of
Unsealing Fire Zone: Case study of Yu Wu coal mine in China
- Authors: Bing Wu, Binbin He, Chenguang Zhao, Baiwei Lei
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  It is very important to unseal the closed coal mine fire zone safely. Although the fire source disappears in the closed fire zone, it is uncertain whether there are still have high-temperature ignition points, and there is a risk of fire or even explosion again after unsealing. To ensure that the closed fire zone can be unsealed successfully at one time, the study puts forward the method of oxygen augmentation observation to understand the combustion state of the closed fire zone in underground coal mine from the perspective of gas analysis technology. When the mine fire is detected to be extinguished, the method is to inject 8–12% oxygen into the fire area, and the fire area shall be monitored for 2 weeks to determine whether the fire area is completely extinguished. The accuracy and practicality of the method of oxygen augmentation observation are verified by comparing and analyzing the difference results generated by two oxygen augmentation observations in closed zone of Yuwu Coal Mine. In this paper, the use conditions of unsealing in fire zone, detailed methods and steps in the whole process of unsealing and emergency rescue plan are given. The research results can provide valuable reference for one-time safe unsealing of fire zone during the process of disaster relief.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-07T10:13:23Z
  DOI: 10.1177/01445987221084379
Multivariate inverse artificial neural network to analyze and improve the
mass transfer of ammonia in a Plate Heat Exchanger-Type Absorber with
NH3/H2O for solar cooling applications
- Authors: Oscar May Tzuc, Jorge J. Chan-González, Iván E. Castañeda-Robles, Francisco Lezama-Zárraga, Moises Moheno-Barrueta, Mario Jiménez Torres, Roberto Best
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  This work presents a numerical approach to compute optimal operating conditions that maximize the absorption flux into a heat exchanger designed for absorption refrigeration systems. Experimental data were obtained from a test circuit that operates in bubble absorption mode with an inner vapor distributor into a Plate Heat Exchanger-type (PHE-type) and interacts with ammonia vapor, NH3-H2O refrigerant, and cooling water. An artificial neural network (ANN) was trained to correlate the thermal properties of the solution and absorption flux in function of easily measurable parameters (concentrations, mass flows, and pressures of saturated and diluted solutions, flow and temperature of the ammonium vapor, environment temperature, and solution temperature). According to results, ANN is adequate to correlate the operational parameters and the transport phenomena inside the heat exchanger with a precision> 99%. ANN also quantitatively identified the ammonium vapor flow (43.1%), dilute solution flow (18.1%), and dilute solution concentration (13.1%) as the variables most importantly in influencing absorption flux optimization. Subsequently, a multivariable inverse artificial neural network was applied to improve the mass transfer into the PHE-type.It was identified that simultaneous optimization of the ammonia and dilute concentration flow rates improves the absorption flow performance by up to 96.3% under a worst-case scenario (ammonia flow rate2.0 kg/min). Finally, it was confirmed that incorporating the diluted solution concentration into the optimization contributes to improving the performance of the absorption process 1%. Results obtained are relevant in the search to produce more competitive absorption cooling systems, demonstrating the feasibility of improving the performance of heat exchangers without structural modifications. The proposed methodology represents an interesting option to be implemented to improve performance in solar cooling systems.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-11T01:09:40Z
  DOI: 10.1177/01445987211073175
Study on the influence mechanism of air leakage on gas extraction in
extraction boreholes
- Authors: Xuebo Zhang, Jianliang Gao, Gaini Jia, Junwei Zhang
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Borehole leakage is an important cause of gas extraction failure. In order to study the influence mechanism of borehole leakage on gas extraction, the borehole air leakage mode was studied, and a mathematical model was established to describe the borehole air leakage of the gas extraction. In addition, this paper also analyzed the change rules of borehole air leakage and gas extraction effect at different borehole sealing depth, negative extraction pressure, degree of fracture development and borehole sealing quality. Research shows that: (1) The hole sealing depth has a certain influence on the borehole air leakage and the gas extraction effect. As the hole sealing depth increased, the borehole air leakage gradually decreased. Moreover, the net amount of gas extraction gradually decreased, but the gas extraction concentration increased to some extent, and the increasing range gradually decreased. The reasonable sealing depth of this coal seam was 9∼10 m. (2) The negative pressure of borehole extraction has little influence on borehole air leakage and gas extraction. With the increase of the negative extraction pressure, the gas extraction net amount and borehole air leakage both increased, but the gas extraction concentration decreased. In the later stage of the gas extraction, the negative pressure can be properly reduced to improve the gas extraction effect. (3) The borehole sealing quality has a great influence on the borehole air leakage and gas extraction effect. With the improvement of the sealing quality, the coal-rock permeability gradually decreased. Moreover, the borehole air leakage significantly reduced, and the gas extraction concentration increased significantly. Therefore, attention should be paid to the selection and improvement of sealing materials and sealing techniques in the actual production so that the airtightness and sealing quality of the hole sealing section can be improved.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-01-19T11:08:54Z
  DOI: 10.1177/01445987211070664
Imperfect detection of spills: A case study in U.S. onshore oil drilling
- Authors: Christopher J. Jablonowski
  First page: 1101
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  This paper specifies and estimates regression models to test several hypotheses about the operational and managerial drivers of pollution in a multi-rig onshore drilling organization. In addition to conventional models, detection-controlled models are also specified to explicitly control for the potential for imperfect reporting. The results suggest that continuity in operations and supervision act to reduce the likelihood of pollution. Additional variables such as site complexity are also significant. The results are largely consistent with related research on personal safety incidents. While the analysis was completed for one organization in one geographic area, the results may be applicable to similar regions and organizations. The results can be used to drive decisions regarding operating practices and managerial policies.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-17T05:55:39Z
  DOI: 10.1177/01445987221087500
Application of integrated drilling and stamping technology in gas
extraction through layer drilling
- Authors: Jinxing Song, Huiyan Zhang, Shiyao Yu, Xianbo Su
  First page: 1113
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  In coal mine gas extraction in China, the current hydraulic permeability enhancement measures generally have complex processes, low adaptability, long operation time, and high labor intensity. This makes it challenging to meet the requirements of coal mining enterprises for safe and efficient mining, and there is an urgent need to develop new technologies to enhance gas extraction and production. This paper proposed an integrated drilling and stamping technology to enhance gas extraction and production and integrates drilling, hydraulic jet fracturing, and hydraulic punching to enhance the permeability of coal seams. A field test was conducted using the specially-developed integrated drilling and stamping equipment to extract gas from the 16101 bottom pumping lane penetration hole in the Jiulishan Mine, Jiaozuo, Henan. The test results show that compared with the hydraulic punching technology previously used in the mine, the punching time of the soft coal seam was shortened by 66–75%, the coal output was increased by 1.7 times, and the punching hole aperture was increased by 1.3 times. Hydraulic injection fracturing was successfully performed to increase the permeability of the hard coal seams, and the fracturing formed a shot hole depth of 345–539 mm. After the integrated drilling and stamping of the drill holes, the coal output, gas extraction concentration, pure gas extraction volume, and coal seam permeability coefficient increased by 2.4, 2.2, 4, and 37.3 times, respectively. The gas flow decay coefficient of the drills holes was also further reduced, which significantly improved the extractionefficiency. Thus the integrated drilling and stamping technology can transform the process of gas extraction from regular extraction to quick, economic, pure, and clean extraction. Thus, this technology has large applicable value for underground gas management in coal mines.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-18T12:25:45Z
  DOI: 10.1177/01445987221078053
Compression characteristics of local filling gangue in Steeply Dipping
Coal Seam
- Authors: Wenyu Lv, Kai Guo, Yongping Wu, Yi Tan, Ke Ding, Bo Li
  First page: 1131
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Coal gangue is widely used as a filling material in coal seam mining. During the gangue filling in steeply dipping coal seam, the loading rate, gangue gradation, and filling speed have an important impact on the deformation and failure of gangue, and further affect the bearing of gangue on overlying strata and the control of surrounding rock movement and deformation. Therefore, this article uses a self-made steel cylinder to conduct a gangue compression test on the HCT pressure testing machine. The research analyzes the influence of loading rate, gangue gradation, and filling rate on the deformation law of gangue in the compression process. After completing the test, the gangues with different particle size groups were rescreened, weighed, and recorded to analyze the crushing situation in the compression process. The results show that loading rate, gangue gradation, and filling speed have greatly influenced filling gangue's bearing capacity, deformation, and crushing rate. The larger the loading rate of gangue, the greater the bearing capacity and deformation of gangue, and the higher the crushing rate of gangue. The smaller the gangue gradation, the smaller the deformation, and the stronger the resistance to deformation. A more optimized gangue gradation ratio is obtained according to the distribution law of the mass proportion of gangue with different particle size groups after compression. The faster the filling speed of manual filling gangue, the greater the strength and deformation of the gangue body. Moreover, the faster filling speed can effectively improve when the strength reaches the peak and deformation tend to be stable. The results can provide theoretical guidance for the local filling of artificial gangue in the longwall working face of steeply dipping coal seam.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-01-21T02:21:58Z
  DOI: 10.1177/01445987211073627
Evaluation of deep high-rank coal seam gas content and favorable area
division based on GIS: A case study of the South Yanchuan block in Ordos
Basin
- Authors: Yutong Fu, Qinghe Niu, Bin Cui, Dan Huang, Xinhan Xie
  First page: 1151
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The South Yanchuan block is the deepest developed high-rank coalbed methane (CBM) field in China, the geological conditions in this block are complex and the main controlling factors of CBM content are various. Thus, a decision-making model of the potential of deep high-rank coalbed methane resource based on geographical information system (GIS) and weighted linear combination (WLC) is established, the influence of geological conditions on CBM content is analyzed, the favorable areas of CBM potential are divided. Results show that the buried depth, coal rank and hydrodynamic condition in the coal seam are dominant factors that control the gas content on a block scale, while the gas content has a weak correlation with maceral composition, coal thickness and the effective thickness of the overlying strata. The study area is divided into five units according to the natural breaks method, i.e., the extramely favourable area, the favourable area, the relatively favourable area, the normally favourable area and the unfavourable area, which account for 14.23%, 22.23%, 24.77%, 25.08% and 13.70% in area, respectively. The extramely favourable area is located in the northwestern of the South Yanchuan block, which is considered to be the key exploration and development area. The study will deepen the understanding of the control of CBM potential in south Yanchuan Block, and is of practical significance for CBM recovery in this area.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-04-12T07:38:26Z
  DOI: 10.1177/01445987221081212
Exploitation of Thar coal field for power generation in Pakistan: A way
forward to sustainable energy future
- Authors: Muhammad Amir Raza, Krishan Lal Khatri, Muhammad Ali Memon, Khalid Rafique, Muhammad Ibrar Ul Haque, Nayyar Hussain Mirjat
  First page: 1173
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Thar desert is located in south-east Pakistan carries 175 billion tons of coal and is the biggest coalfield in Asia. In this paper mathematical framework is developed for the accurate estimation of power production from the available Thar coal capacity. Annual TWh possible energy production the period 2020 to 2040 followed by detailed analysis of capacity factor and Maximizing the share percentage of coal in total energy mix at least 40% by 2040 is presented. The findings reveal that Thar coal has the capability of producing 100,000 MW power up to the next 250 years. The energy generation for the years 2020, 2032, and 2040 is calculated 744 TWh per year, 700 TWh per year, and 665 TWh per year respectively and it produces negligible negative impacts on the environment. The long-term energy planning presented in this paper would attract foreign investment and Pakistan's energy needs would be fulfilled for sustainable development of the country.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-23T01:44:42Z
  DOI: 10.1177/01445987221082190
Study on instability discriminating condition and permeability variation
of triangle articulated structure in highly inclined goaf
- Authors: Song Qin, Haifei Lin, Zongyong Wei, Wei Shen
  First page: 1197
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The huge, inclined goaf formed by the mining of steeply inclined and extra thick coal seams has the characteristics of occupying a large space and being subject to complex breaking behavior of its overlying rock structure, especially the rock block structure characteristics of the interface area between the goaf and the lower working face which is difficult to be characterized, leading to a hidden danger when mining the lower working face. In response to the aforementioned problems, the following conclusions are drawing as follows: (1) with the aid of the contradiction method, the critical condition governing instability of the triangular articulated structure was obtained to explain the correctness of the assumption of the triangular hinged structure; (2) three-point truss structure was composed of key layer blocks; (3) in the stabilization stage of the triangular hinged structure, the fracture network area was extracted, and the centerline intensive equivalent method of a single fracture segment was adopted to directly measure the equivalent length. Meanwhile, the value of equivalent average width with the equivalent length of a single crack was calculated by integral operation and equivalent figure calculation; (4) the mathematical expressions of permeability which was positively exponential function related to the ratio of equivalent average width to equivalent length were derived. Furthermore, the vectorized solution of seepage rate was carried out respectively for the goaf area and the extracted network area by using COMSOL software. The distribution of the strong seepage area of CBM and the ratio of equivalent average width to equivalent length is found to be consistent to a large extent, which provides theoretical support for subsequent CBM management.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-18T03:37:01Z
  DOI: 10.1177/01445987221077364
Source identification of mine water inrush based on the exponential
whitenization function and the grey situation decision model
- Authors: Daokun Wang, Qiding Ju, Yuquan Wang, Youbiao Hu, Qimeng Liu, Huichan Chai, Yu Liu
  First page: 1217
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Coal mining at deep levels can cause mine water inrush and groundwater contamination, making it important to accurately and rapidly identify the water inrush source. In this study, 52 water samples were extracted from three types of aquifers in the Linhuan mining area, China. The water sample components Na+ + K+, Ca2+, Mg2+, HCO3−, Cl−, and SO42−, measured in the experiment, were used as evaluation variables, and the piecewise function equation was established by using the exponential whitening function. Finally, combined with water sample data and the CRITIC weighted grey situation decision-making method, the comprehensive membership degree was obtained, and the water inrush source was identified according to the principle of the maximum membership degree. The comprehensive accuracy of the model was 92.3%. The traditional grey situation decision-making method uses the linear whitening function to determine the membership value, ignoring that the value of the whitening function outside the adjacent level is 0, which improves the weight of the adjacent level, causes the loss of effective information, and reduces the discrimination rate. The exponential whitenization function in this paper will solve this problem and further improves the grey situation decision-making method to discriminate the water inrush source, which would also be beneficial regarding the prevention and control of mine water inrush and groundwater contamination.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-15T08:32:57Z
  DOI: 10.1177/01445987221085607
Potentially Economic Concentrations of Rare Earth Elements and Gold in
Power Plant Coal Combustion Products (Far East, Russia)
- Authors: Sergey V. Dugin, Anatoly P. Sorokin, Valery M. Kuz’minykh, Andrey A. Konyushok
  First page: 1236
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  The distribution of rare earth elements (REE) and gold (Au) in fly ash released during combustion of brown coal from the Pereyaslavskoye (Siberia) and Erkovetskoye (Far East) deposits has been investigated. Coal combustion was carried out in two locations: the boiler unit of the Blagoveshchenskaya coal-fired power plants (CFPP), equipped with an electrostatic precipitator (ESP); and at the Amur Experimental and Technological Complex (ETC) with the aim of separating the combustion products (slag, fly ash, sludge). It was found that in both processes the highest contents of REE (400 and more ppm) and Au (up to 0.29 ppm) are concentrated in fly ash. These characteristics of coals were used as the basis for the author's calculation of the predicted resources of REE and Au under the conditions of the annual operation of firstly one boiler unit, and then five, equipped with an ESP. Further research by the authors will be aimed at improving the degree of recovery of concentrates through the development of technologies at pilot plants such as ETC “Amur”.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-09T01:32:33Z
  DOI: 10.1177/01445987221078054
Complex Fracture Closure Pressure Analysis During Shut-in: A Numerical
Study
- Authors: Daobing Wang, Hongkui Ge, Xiaoqiong Wang, Yang Wang, Dongliang Sun, Bo Yu
  First page: 1252
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Conventional fracture closure models typically assume homogeneous formation. This assumption renders complex fracture closure pressure analysis during shut-in insufficient at present. In this paper, we use a cohesive zone method (CZM)-based finite element model to obtain the fracture closure pressure and minimum horizontal principal stress of the major fracture and the branch fracture based on pressure fall-off analysis. Key factors including leak-off rate, injection time, and stress anisotropy are discussed in detail. A quantitative relationship between fracture closure pressure and these factors is plotted to reduce or eliminate the errors caused by conventional fracture injection diagnostic models. The results show that leak-off rate, injection time, and stress anisotropy have a significant effect on the fracture closure process. Fracture closure in naturally fractured formations is a slow process, and the early closure pressure represents the closure of the branch fracture, which is much higher than the minimum horizontal stress. This investigation provides new insight into how to estimate the in-situ stress in naturally fractured reservoirs.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-02-10T09:28:07Z
  DOI: 10.1177/01445987221077311
Methods for geothermal resource assessment of hot dry rock: A case study
in the Gonghe Basin, China
- Authors: Lei Fu, Dongguang Wen, Qingda Feng, Senqi Zhang, Xin Ma, Linyou Zhang, Wei Shao
  First page: 1268
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Hot dry rock (HDR) geothermal resources are renewable energy source. Many of the findings of HDR resource evaluations have been used in energy planning and EGS design. However, to assess the amount of HDR resources in different locations, a consistent classification scheme and evaluation methods are still lacking. Considering geological credibility and economic feasibility, HDR resources are separated into three categories: vision, reserve, and exploitable. Vision and reserve are stationary resources that can be evaluated using the volume technique, and the exploitable resources can be evaluated using the numerical simulation approach. The HDR vision resource of the Gonghe Basin is evaluated to be 4.076 × 1022 J, and the reserve resource of the Qiabuqia HDR mass is evaluated to be 2.11 × 1020 J. At the Qiabuqia HDR development site, a discrete fracture network (DFN) model is applied for numerical simulation computations, which is based on the notion of local thermal nonequilibrium. The K1 and K2 wells produce varying amounts of heat due to the heterogeneous features of the fractured medium model, which is primarily due to differences in fracture density, heat exchange area, and fluid migration pattern. The categorization system and assessment technique can be used as a guide for evaluating HDR resources in the future.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-03-14T11:44:18Z
  DOI: 10.1177/01445987221075847
Waste-to-energy in a developing country: The state of landfill gas to
energy in the Republic of South Africa
- Authors: Setlamorago Jackson Mbazima, Masilu Daniel Masekameni, Daniel Mmereki
  First page: 1287
  Abstract: Energy Exploration & Exploitation, Ahead of Print.
  Landfill gas to energy (LFGE) projects were implemented in the Republic of South Africa (RSA) to diversify the energy mix and transition to a green economy. This study provides an overview of the status of LFGE in RSA and identifies major factors that inhibit the adoption and utilization of this technology, using existing data from 2010–2020 from electronic databases, namely, ScienceDirect, Taylor & Francis, Google Scholar, Sage Open, Springer Link, Sabinet, and IEEE Xplore, and using a combination of keywords and Boolean functions. This study revealed that, although RSA has made significant progress in the adoption and utilization of landfill gas (LFG) through the seventeen (17) planned LFGE projects, only six (6) are operational and generate 15 MW of electricity supplied to the local grid in the KwaZulu-Natal, Western Cape, and Gauteng Province. The waste-to-energy (WtE) sources such as LFGE are not given priority, and the country continues to invest in coal-fired power stations, owing to the abundance, availability, and low cost of coal reserves, which will supply coal for the next 200 years. The study identified factors inhibiting LGFE projects in RSA, which included the lack of sanitary landfill sites, LFG monitoring, funding, skills, research, and development. Potential LFGE in RSA is evident, however, except for limited processing facilities, economic investment, and public awareness. Suggestions for further research on the techno-economic and policy assessments are provided in the study. This study contributes to synthesizing evidence of the status of LFGE, insights on state-of-the-art technologies of WtE and the associated challenges in the waste management sector, identifying the potential for LFGE, and LFGE in the circular economy, and building a foundation for future research on WtE such as LFGE. Moreover, it also offers a reference for policymakers, decision-makers, researchers in the waste management sector on the technologies of WtE, LFGE, and potential to reduce waste generated.
  Citation: Energy Exploration & Exploitation
  PubDate: 2022-04-25T05:37:29Z
  DOI: 10.1177/01445987221084376