The objective of this study is to demonstrate the feasibility of acquiring geothermal energy from existing abandoned oil and gas wells. The equations describing the heat exchange between fluid and ...rocks are developed, and parametric studies are conducted in order to specify the optimum values of the main parameters. Computational results indicate that the geothermal energy produced from abandoned wells depends largely on the flow rate of fluid and the geothermal gradient. The temperature of extracted liquid is 129.88 °C, and it drops to 127.92 °C after ten years of operation. It is observed that both hot water and electricity can be acquired from the abandoned wells. Results also indicate that the distance of two wells should not be less than 40 m in order to avoid interaction between them. Furthermore, the financial reward of electricity is 36833.26 US $/year for a retrofitted well.
► We demonstrate the feasibility of acquiring geothermal energy from abandoned wells. ► It costs lower to modify abandoned oil and gas wells to become geothermal wells. ► The geothermal system can operate steadily for a long time. ► The financial reward is 36833.26 US $/year for a single well.
Abstract
As a mixture of soil and rock, the deformation of surrounding rock caused by tunnel excavation in the sandy cobble stratum is affected by the meso-structure of the stratum. In this paper, ...the mechanical and engineering characteristics of sandy cobble soil are studied in depth using a laboratory large-scale triaxial test and discrete element numerical simulation test, and the effects of main microscopic parameters on the characteristics of sandy cobble soil are analyzed, including the same specimen size, moisture content, compactness, confining pressure as well as loading method. The microscopic parameters such as contact modulus
E
c
, friction coefficient
f
r
, and stiffness bond ratio
n
of sandy pebble soil can be obtained. Meanwhile, the accuracy and uniqueness of microscopic parameters are determined using the response surface method. Moreover, the influence of different contact modulus and friction coefficient on the macroscopic mechanical properties of sandy pebble soil is quantitatively analyzed. The obtained conclusions are drawn as follows: the elastic modulus of sandy pebble soil decreases with the increase of water content. The peak value point of the stress-strain curve of sandy pebble soil increases with the increase of contact modulus and friction coefficient, respectively. The relationship between peak stress and the two types of fine-scale parameters can both be described by logarithmic functions. Compared to fine-grained soils, sandy pebble soils start to break down at about 3.5% of the axial strain, and the sandy cobble soil can still bear a certain load after reaching the peak strength. The results can provide a reference for the calculation and discrete element simulation of tunnels in sand and pebble strata.
Rapid and sensitive detection of mercury vapor is of great significance for environmental protection and human health. But the detection method enabling low detection limitation and rapid response at ...room temperature simultaneously has rarely been reported. In this work, we propose a gold particles decorated reduced graphene oxide sensor for mercury vapor detection. After adding the gold particles, the reduced graphene oxide sensors’ response sensitivity increase by more than 16 times and the response time significantly decreases, which is far less below the results reported by others. The sensor performance improvement should attribute to the distribution of the decorated gold particles, which insert into the layered graphene sheets, as demonstrated by the SEM and XRD results. The increased layer spacing of graphene sheets is conductive to the faster entry/exit of mercury vapor and increases the effective sensing area of graphene. What’s more, the first-principles calculation results confirm the mercury-philicity of gold particles, which also contributes to the increased sensitivity. We further test more performance of the gold particles decorated reduced graphene oxide sensor to mercury vapor, which shows a linear response, low detection limit and good repeatability. The proposed sensor shows rapid response/recovery (6/8 s), low detection limit (0.01 ng/mL), linear response, good repeatability and room temperature detection simultaneously, which shows great application potential for mercury vapor detection.
•A new mercury gas sensor is proposed and prepared by gold particles decorated functionalized graphene.•The mechanism of gold particles on the improvement of sensor response are explored through simulation and experiments.•Wide detection range, low detection limit, rapid response and recovery are realized simultaneously under room temperature.•The sensor shows high potential to be applied in the fields of mercury vapor detection.
To reduce the application dosage of thiamethoxam (TMX), we investigated the deposition and dissipation patterns in a pepper-planted ecosystem under different planting modes across four regions in ...China, namely Hainan (HN), Zhejiang (ZJ), Anhui (AH) and Hebei (HB). This study focused on the deposition and dissipation of TMX at concentrations of 63.00, 47.25, 31.50, 23.63 and 15.75 g a.i.hm
. As the application dose increased, the deposition amount of TMX initially increased in the plants and cultivated soil, showing obvious geographic differences in four cultivation areas. Surprisingly, the initial amount of TMX deposited the pepper-cultivated greenhouse of ZJ and AH was 1.1-2.1-fold and 1.0-3.6-fold higher than that in the open field system at the same application dose, respectively. In pepper leaves, stems, fruits and soil, the dissipation exhibited rapid growth and then slowed. However, the residual concentration showed an increasing trend, followed by a subsequent decrease in the pepper roots. In different planting regions, the dissipation rate of TMX followed the order HN > ZJ > AH > HB in pepper plants and cultivated soil. In comparison to the open field, the total TMX retention rate in greenhouse was higher, indicating overall greater persistence in the greenhouse conditions. These findings reveal the deposition and dissipation characteristics of TMX within the pepper-field ecosystem, offering a significant contribution to the risk assessment of pesticides.
In this study, a new empirical model is proposed for estimating daily global solar radiation on a horizontal surface by the day of the year. The performance of the proposed model is validated by ...comparing with three trigonometric correlations at nine representative stations of China using statistical error tests such as the mean absolute percentage error (MAPE), mean absolute bias error (MABE), root mean square error (RMSE) and correlation coefficients (
r). The results show that the new model provides better estimation and has good adaptability to highly variable weather conditions. Then the application of the methodology is performed for the other 70 meteorological stations across China.
To solve the engineering problem of the first tunnel lining cracking caused by the second tunnel construction of double-arch highway tunnels, a research method combining distributed optical-fibre ...monitoring, inversion analysis and numerical simulation that can reflect lining cracking was presented. Optical fibres were laid on opposite sides of the steel arches inside the first tunnel lining. Embedded optical-fibre monitoring was conducted continuously during the second tunnel driving. Based on the fibre-optic strain profile, the lining cracking was deduced and warned in time. The mechanical behaviour of the steel arch was investigated by the inversion analysis, which took into consideration the integrated impact of axial force and flexural moment. A two-dimensional (2D) load-structure method–based numerical model was established, considering the influence of different load distributions in each construction condition. The total strain rotating crack constitutive model was applied to reflect the cracking behaviour of concrete lining in the simulation, and the model was calibrated and verified in the laboratory. Comparative analysis between the simulated strain distribution and the distributed optical-fibre monitoring results was carried out. The deformation mode and crack distribution of the lining were analysed. The cracking mechanism was explained. Specifically, the second tunnel construction led to the loading at the top of the middle partition wall and the release of rock pressure in the first tunnel. Under these load changes, the secondary lining of the first tunnel cracked on the inner side of the top of the middle partition wall owing to tension, and compression-bending failure occurred near the right arch foot. Finally, the influence of the parameters on the lining force was analysed, and a construction optimisation scheme was proposed.
The control mechanism of prestressed support system is studied by means of three-dimensional discrete element numerical simulation, theoretical analysis, and field measurement. The actual project is ...selected to analyze, and the control effect is demonstrated. The theoretical analysis results show that the prestressed support can improve the self-bearing capacity of surrounding rock, which is conducive to the stability of the surrounding rock. The numerical calculation shows that, under the control of the long and short cables, the prestress can spread effectively and form two bearing arches. The deformation is difficult to control, which is in the arch crown and the arch shoulder of the tunnel intersection. However, the deformation of the surrounding rock decreases with the increase of prestress. Through the analysis of the measured results, it shows that the pretension support design scheme can effectively control the large deformation of the surrounding rock.
Solar radiation measurements are not easily available, especially for the diffuse solar radiation. In this study, two models for estimating the diffuse solar radiation are proposed based on multiple ...predictors including the clearness index, relative sunshine duration, ambient temperature and relative humidity. One of them aims to increase the estimation accuracy, and the other aims to estimate the diffuse solar radiation direct from other meteorological elements in the absence of the global solar radiation. For a case study, the performance of the proposed models is validated by comparing with eight existing models selected from literature against the measured data at Guangzhou station in China. Through the analysis based on statistical error tests, results show that the two models can estimate the monthly average daily diffuse solar radiation with good accuracy.
► Two models for estimating the diffuse solar radiation are proposed. ► One model aims to increase the estimation accuracy. ► The other model aims to work with the global solar radiation unavailable. ► For a case study, the proposed models are validated at Guangzhou station in China.
Eight models using only the sunshine duration for estimating the global solar radiation on a horizontal surface are evaluated at Changdu, Geer, Lasa and Naqu stations in Tibet, China against the ...measured meteorological data during 1994–2008. Based on statistical error tests, results show that the simple linear Ångström–Prescott model is reasonably accurate in practice, and the modifications with complex expression are not necessary in Tibet. Then, two general Ångström–Prescott models for estimating the daily and monthly average daily global solar radiation respectively in Tibet are proposed.
► Eight sunshine-based models are evaluated against the measured data in Tibet. ► The simple linear Ångström–Prescott model is reasonably accurate. ► Modifications with complex expression to Ångström–Prescott model are not necessary. ► Two general Ångström–Prescott models for Tibet are proposed.
The MPW that emits from a tunnel’s exit when a high-speed train passes through is a serious environmental problem which increases rapidly with the speed of the train. To alleviate the MPW problem at ...400 km/h, the aerodynamic effects caused by the hood located at the entrance or exit of a tunnel are studied by numerical method, and the influences of hood geometry, such as an enlarged cross-section, oblique entrance, and opening holes on the MPW, are also investigated. The research indicates that the enlarged cross-section of the hood at the entrance and exit of the tunnel has opposite effects on the MPW, and the oblique section can alleviate the MPW by extending the rising time of the compression wave and increasing the spatial angle at the hood exit. The pressure gradient can be mitigated through delaying the rising of the compression wave by opening holes on the side wall of the hood, and the relief effects of the holes can reduce the MPW further. The MPW problem when a train passes through a tunnel at 400 km/h can be effectively alleviated by an optimized oblique enlarged hood with opening holes, even up to train speeds of 500 km/h.
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