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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] In this study environmental radioisotopes of water (3H and 14C) were used to determine the residence time of thermal waters. The temperature of geothermal waters was found to be uniform (57.6 °C ± 0.75 °C) with similar field alkalinity and pH values. The δ13C values of thermal water ranged between - 21.3 and - 18.75 ‰, which clearly reflect no/minimum contribution of carbonate minerals to the system. Environmental tritium concentration was found to be very low in these thermal waters indicating insignificant recharge from modern sources. The Pearson modelled 14C ages were found to vary from 4964 to 17,714 years. (author)
[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.
'Very-low-energy' geothermal energy in collective housing and office building. From theory to practice, already present and actual solutions in Bourgogne + exemplary operation of energy efficiency for the sustainable development of buildings and collectivities: Le Pre de la Cour housing development in Sennece-les-Macon (71) new construction of 10 rented detached houses heated by heat pumps on underground vertical captures
[en] This publication first indicates the different types of geothermal energy exploitation, and briefly describes the operation principle of a heat pump. Sheets then present different types of installations (heat pump on aquifer, heat pump on geothermal captures, heat pump on waste waters) with a description of the principle and installation, an indication of benefits and drawbacks, and of the regulatory context, and brief presentations and descriptions of corresponding examples realised in the region. Concerned standards are mentioned. An example (a housing development of detached houses equipped with heat pumps on underground vertical captures) is then presented: approach and methods, solutions and their implementation (high performance envelope and venting, high performance heating systems and equipment, high performance cooling systems and equipment, energy consumption follow-up devices), results, and lessons learned
[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] World energy demand is increasing and non-renewable resources are decreasing by exponentially putting a huge burden on the energy sector specifically on the oil and gas industry. To overcome these challenges, renewable energy is the best option with production optimization in the oil and gas sector. However, among all renewable energies, geothermal is the most suitable energy due to its sustainability and presence around the clock. Moreover, there are three types of wells for harnessing geothermal energy such as: producing oil and gas well, abandoned oil and gas wells and geopressured brine well with dissolved gas. In this research study, the author’s considers the technical aspects of electricity generation through oil and gas wells. The power capacity of these wells is determined by the production rate of the well mass flow (m) and temperature (T) of these wells. The main factors that control the wellhead temperature are mass flow rate and formation temperature. Our assessment of gas-producing well in the Kandhkot region showed the wellhead temperature of the produced fluid is too low, compared to ambient temperature for commercial generation of geothermal power. In our work, a conceptual design system to produce power from produced gas by using Solid Works Software is proposed and we have found some positive results. Seven well from the Kandhkot gas field were selected with different mass flow rates and negligible wellhead temperature difference. Author’s found the minimum power net output 21kW at the gas mass flow rate of 0.098504 kg/s with 7.5% thermal efficiency and maximum net output 27.5 kW at gas mass flow rate of 4.102524 kg/s with 10% thermal efficiency. The overall net output power produced from seven well is 174kW and can supply to local communities. (author)
[en] Energy is only a utility, it should not lead to feelings or dreams; it is only a question of choosing the most efficient means of heating, cooking, moving, machining, etc., while preserving a pleasant environment. Whether by one means or another, this in itself is of no importance to the citizen. However, if we look at statements and positions, this rationality is often absent; orders of magnitude, availability in space and time, are often forgotten. We move from the pilot experiment to the upheaval of society, forgetting the stages that can be dead ends. We confuse objectives and means by getting enthusiastic about attractive but unrealistic ideas
[fr]L'energie n'est qu'une utilite, elle ne devrait entrainer ni sentiment ni reve; il s'agit seulement de choisir les moyens les plus efficaces pour se chauffer, cuisiner, se deplacer, usiner, etc., tout en preservant un environnement agreable. Que ce soit par une voie ou par une autre, cela n'a pas d'importance en soi pour le citoyen. Pourtant, si l'on regarde les declarations et prises de position, cette rationalite est souvent absente; les ordres de grandeur, les disponibilites dans l'espace et dans le temps, sont souvent oublies. On passe de l'experience pilote au bouleversement de la societe en oubliant les etapes qui peuvent etre des impasses. On confond objectifs et moyens en s'enthousiasmant sur des idees seduisantes mais irrealistes
[en] Highlights: • A model is proposed for U-shaped closed loop geothermal well. • New concepts of critical position and effective distance are proposed. • Optimal injection parameters are discussed based on effective distance. - Abstract: At present, geothermal energy is a promising research area but with a series of unknowns waited to be explored. Recently, the U-shaped closed loop geothermal extraction system was proposed to improve the geothermal recovery performance. However, there is a lack of mathematical model to simulate the circulating process of CO2 in the wellbore. In this paper, a model is developed for simulating CO2 flow in the descending, horizontal and ascending sections of the geothermal well. Besides, in order to properly evaluate the geothermal recovery performance, two new concepts of critical position and effective distance are proposed. Simulation results show that: (a) There exists a critical position in the ascending wellbore where the working fluid temperature is equal to the formation temperature. (b) The effect of mass flow rate on pressure drop becomes more obvious when the gravity is neglected, especially under the condition that the mass flow is at a higher value. (c) The rapid increase of working fluid temperature does not mean that the geothermal recovery performance is better. At this time, the effective distance should be adopted as an additional reference.