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[en] Rock fracture mechanics have been widely applied to earthquake mechanics, hot dry rock geothermal energy extraction, hydraulic fracturing, mechanical fragmentation, rock slope analysis, geophysics, and many other practical problems. It is important for geological disaster identification and prevention to clarify the crack propagation mechanism in rock failure process. To further investigate the evolution of crack propagation and internal damage in brittle rock, and based on the way that rock mainly occurs shear failure, we conducted direct shear tests on sandstone. Our tests combined macroscopic/mesoscopic observation and acoustic emissions monitoring. We found that crack propagation under compressive-shear stress occurs in stages, including the initiation and propagation of tension cracks, which are then connected by shear cracks. As normal stress increases, the length of a single tension crack becomes shorter, and the cracks themselves increase in number. We found that tension crack propagation is accompanied by fewer microcracks; in contrast, shear crack propagation is accompanied by considerable microcracks. This process may induce a drop off in mineral particles through slipping, and it may ultimately produce a rock bridge. The main damage occurs after shear cracks appear during shear failure, especially when the normal stress increases. (paper)
[en] The paper conducts comparative analyzes of the advantages and disadvantages of existing and currently used in the countries of the world, including Azerbaijan, domestic energy sources, and also indicates the environmental and economic advantages of using, in future energy, alternative and renewable energy sources (ARES). For this purpose, a special analysis method is used. The results are presented in tabular form.
[en] Alsace possesses the most powerful hot water springs in France at accessible depths. This article presents the activities of the Fonroche Geothermie company which started the first project of deep geothermal energy near Strasbourg, more precisely on the site of the Vendenheim Rhine eco-park. The budget and financing actors are indicated. The techniques and works are described. Water at 200 degrees Celsius has been reached at a depth of 4600 meters. Exploitation is expected to start in 2020. Some future projects are mentioned in the same region and in others as well. Objectives in terms of price are discussed, and the interest of foreign actors is mentioned
[en] Geothermal energy is renewable and emits only minute amounts of carbon dioxide gas. It can be the most effective energy source not only economically but also environmentally when considering power generation for remote and relatively small islands like those in Eastern Indonesia. For the development of geothermal energy in the islands, magnetotelluric (MT) surveys have been conducted, but failed to properly image the electrical conductivity structure of the subsurface due to the impact of the existence of the surrounding sea, known as the ‘sea effect’. MT data are severely distorted by the electrical conductivity of seawater and thus should be corrected before inversion or directly inverted to take into account the sea effects. However, both strategies can be effective only when the sea effects at a target area are properly simulated. This study investigated sea effects at Atadei geothermal field in Lembata Island to build a resistivity model that can accurately describe sea effects. In the process of determining the proper sea model, we constructed several sea models of Lembata Island, and compared simulated MT responses for each model in order to analyze the sea effects. The process can serve as a good strategy in dealing with MT data obtained in islands located in complex sea environments. Our future work will interpret the MT data using the properly constructed sea model. (paper)
[en] In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks.
[en] This article provides the review of thirty chemical geothermometers of foreign authors for estimation of water temperature in geothermal aquifers in the central depression of the Danube Basin. The results of estimated water temperatures using chemical geothermometers were compared with the temperatures measured in respective geothermal boreholes. Consideration of the comparison resulted in a summary including selection of most suitable chemical geothermometers for each site to be used in hydrogeothermal praxis for water temperature determination. (authors)
[en] Highlights: • A novel combined power and water system is proposed. • Energetic, entropy and exergetic analysis of the combined system is achieved. • Cost of the heat and mass transfer areas is calculated. • Correlations between the system performance and the evaporation temperature are focused. - Abstract: This paper proposed a novel combined system to achieve the cascade utilization of geothermal energy for joint power and water production. A regenerative organic Rankine cycle (ORC) is adopted as the top cycle, while a desalination system based on humidification dehumidification (HDH) principle with open-air architectures is applied to further utilize the geothermal energy. Based on the streams within the ORC and HDH units, the corresponding mathematical models with mass and energy conservation are established, and performance simulation according to thermodynamic laws is fulfilled. Furthermore, cost analysis of the combined system is also accomplished to reveal the correlations between the system economy and the involved parameters. The research results show that the actual peak values of net power, water production and gained-output-ratio (GOR) reach 42.68 kW, 236.81 kg h−1 and 1.42, and the total efficiency of the entire system is 31.19%. Based on the obtained thermodynamic performance, the bottom cost of the entire system is found as 4983.83$ with a total heat and mass transfer areas of 104.27 m2 at the balance condition of the humidifier. Furthermore, according to the influence analysis, an elevation of the evaporation temperature of the ORC, which is within the prescribed range, is beneficial to improve the thermodynamic performance and the relevant cost of the combined system.
[en] Geothermal energy remains a largely undeveloped natural resource because of the high risk associated with its development. An accurate prediction model for easy identification of potential regions can help to lower the risk and cost associated with development. In this study, geothermal potential regions were identified through the relationship between geothermal emergencies and their controlling factors in Tengchong County, China. Publicly available databases for this analysis including epicenters, active faults, Bouguer gravity, Landsat7 Enhanced Thematic Mapper Plus images, the magnetic data and digital elevation model data were extracted as the b-value map, distance to faults map, distance to main grabens map, land surface temperature map, magnetic anomaly map and distance to rivers map, respectively. Based on the platforms within geographic information system, an entropy theory-integrated information model was established to evaluate the geothermal potential sites within the region. Moreover, factor analysis method was applied to test the conditional independence between the map pairs before modeling application. The results of the weighted information model show that the model shows perfect performance in discovering potential geothermal regions. In the final maps, undeveloped or unexploited geothermal regions can be observed along the Mingguang River and Nu River. Undeniably, these models will help to find undiscovered geothermal regions with limited geological information publically available.
[en] Highlights: • A numerical model of reaction for thermal spallation drilling is proposed. • The reliability of the numerical model is validated in experiment. • Characteristics of reaction flow field are investigated. • Effects of dimensions of the reactor on the flow field are studied. - Abstract: Thermal spallation technology is an alternative drilling method, which has the potential to exploit petroleum and geothermal energy with low costs. In this paper, the influence of the structure of the reactor on the characteristics of the flame jet is analyzed from aspects of outlet velocity, temperature, pressure and mole fraction. The Peng-Robinson equations of state and eddy dissipation model are applied in the simulation. An experimental setup is designed and experiments are performed to validate the simulation results. Results show that the reactor length and nozzle length can be reduced in a proper range to obtain better results. The suitable nozzle diameter may be changed for different types of rock to obtain the best rate of penetration. Also, no cooling water may be injected until the temperature of the reactor wall reaches the limitation of failure. Results could provide guidance for field applications.