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AbstractThe hydrogeochemical characteristics and isotopic analyses of geothermal water are effective in the genetic study of a geothermal system. This study systematically investigated the geochemical and isotopic compositions of the geothermal water in the Qutan and Reshuizhou geothermal fields. The geothermal water in these two fields is of HCO3 (·F)-Ca·Na type and has undergone protracted water runoff and deep thermal cycle. Based on the mineral-water solubility equilibrium, the reservoir in the Qutan geothermal field has a temperature of 60–74°C and a depth range of 770–1003 m. The geothermal water in the Reshuizhou geothermal field has been mixed with cold water, which accounts for 58% in weight. The reservoir in the Reshuizhou geothermal field has a temperature range of 131-150°C and a depth range of 1953–2287 m. The geothermal water in the Qutan and Reshuizhou geothermal fields have 14C ages of 8251–7961 BC and 3514–2254 BC, respectively, which are consistent with the result of the 3H isotopic analyses. When recharging and transiting to geothermal water, the meteoric water underwent changes in geochemical compositions, which were dominantly controlled by water-rock interactions, including the precipitation of chalcedony and muscovite and the dissolution of calcite, fluorite, K-feldspar, and albite. In the Reshuizhou geothermal field, the hydrogeochemical compositions of the geothermal water are affected by cold water mixing.

AbstractWildfire is an integral part of the Earth’s climate system and plays an important role in shaping terrestrial ecosystems and biodiversity, atmospheric chemistry, regional climate, and the carbon cycle in the Earth’s history. However, the lack of high-resolution records of long wildfires limits our understanding of the natural variability, long-term trends of wildfire activity, and the reasons behind the changes in wildfire on orbital timescales. Here, a 320 ka long high-resolution wildfire record from the subarctic North Pacific is reconstructed with black carbon (BC), including its two subtypes char and soot. A 7-day-long back trajectory simulation analysis reveals the higher frequency of trajectories comes from Siberia. Our data show that continuous incidence of wildfire on a continental scale over the last 320 ka was higher during glacial periods than during the interglacial periods. The increase in wildfire frequency during glacial periods is ascribed to less precipitation. Contrasting patterns of wildfire incidence between marine isotope stages 2 and 6 may be ascribed to different fuel availability, which is related to contrasting configurations of the Northern Hemisphere ice sheet between glacial periods. A significant periodicity of 23 ka of our wildfire record suggests the precession of the Earth’s orbit pace wildfire development. The tight coupling of intensified wildfire and enhanced nutrient utilization efficiency suggests a nontrivial role of fire in the climate system.

AbstractReinjecting low-temperature tailwater into geothermal reservoirs leads to complex thermo-hydro-mechanical coupling processes, making it more difficult to predict the thermal breakthrough of the reservoirs. By taking the example of the deep carbonate geothermal reservoirs of karst fissure type in the Xianxian geothermal field in China, this paper studied the thermo-hydro-mechanical coupling processes in the case of reinjection based on previous tracer tests. It established a thermo-hydro-mechanical three-field coupling model based on a two-dimensional discrete fracture network and further verified its suitability through inversion analyses. Moreover, this paper discovered the regularity of the effects of temperature and pressure changes on the deformation of the rock masses in geothermal reservoirs and clarified the mechanisms of the seepage and heat transfer in thermo-hydro-mechanical coupling processes. Meanwhile, it presented the effects of the pressure and temperature on the heat extraction efficiency and production well temperature of the geothermal production-reinjection system in the Xianxian geothermal field. As indicated by the results, the pressure and temperature of geothermal reservoirs increased and decreased, respectively, in the initial phase of the reinjection, leading to an increase in fracture aperture and reservoir permeability. Then, they tended to gradually stabilize, and the amplitude change of the reservoir permeability decreased as the reinjection proceeded. Finally, this paper proposed an optimized reinjection scheme of the study area, aiming to provide scientific support for geothermal reinjection.

AbstractLarge-scale geothermal production based on a multiwell layout has been promoted by the development of clean energy. However, the theories about the effects of this geothermal production pattern on the temperature field of geothermal reservoirs are yet to be improved, which hinders the design optimization of the deployment schemes of geothermal wells. This study proposed a 3D geothermal multiwell simulation method covering the heat transfer in wellbores by introducing the geothermal well theory of 1D line elements, thus improving the calculation efficiency without reducing the calculation accuracy. By taking the geothermal development using multiple wells in the Xianxian geothermal field, China, as an example, this study firstly analyzed the evolution of the temperature field in geothermal reservoirs during the geothermal exploitation based on a multiwell layout. Then, it revealed the influencing mechanisms of geothermal multiwell effect, reinjection depth, and well spacing on the thermal breakthrough of exploitation wells. Finally, it proposed an optimized design method for the geothermal development based on a multiwell layout. All these will provide scientific support for the large-scale geothermal production based on exploitation-reinjection combination using multiple wells.