Geothermal energy is a kind of renewable,sustainable and clean energy resource.Geothermal energy is abundant in carbonate reservoirs.However,low matrix permeability limits its exploitation.The super-critical carbon di...Geothermal energy is a kind of renewable,sustainable and clean energy resource.Geothermal energy is abundant in carbonate reservoirs.However,low matrix permeability limits its exploitation.The super-critical carbon dioxide(SC-CO_(2))jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO_(2) simultaneously.In this paper,we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of sc-CO_(2) jet fracturing.The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface.The physical properties change of sC-CO_(2) with temperature were considered in the numerical model.Results showed that SC-CO_(2) jet frac-turing is superior to water-jet fracturing with respect to jetting velocity,particle trajectory and pene-trability.Besides,stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO_(2) jet than that by water jet.Moreover,pressure and temperature control the jet field and seepage field of sC-CO_(2) simultaneously.Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO_(2).The key findings are expected to provide a theoretical basis and design reference for applying SC-CO_(2) jet fracturing in carbonate geothermal reservoirs.展开更多
The hydrogeochemical characteristics of geothermal fluids can reveal the genesis of geothermal systems and act as important references for developing and using geothermal resources.This study presents hydrogeochemical...The hydrogeochemical characteristics of geothermal fluids can reveal the genesis of geothermal systems and act as important references for developing and using geothermal resources.This study presents hydrogeochemical processes and thermal cycle mechanisms of typical geothermal fields in Western Sichuan.Based on the geological conditions in Western Sichuan,29 hot springs in three geothermal fields in the Batang and Litang areas were selected for hydrochemical and isotopic(δD andδ18O)analyses.Furthermore,the temperature of the thermal reservoir was calculated and the upflow cooling process of the hot springs was analyzed.Most of the subterranean hot waters in Batang and Litang are of the HCO3-Na hydrochemical type.The ion variation in Batang is primarily affected by water-rock interactions.There is a strong positive correlation between Na+,B?,and Cl?in Litang,suggesting that they have the same material source.The Na+and metaboric acid content is relatively high,which indicates that the groundwater runoff in both areas is relatively long-lasting,with reduced flow velocity;moreover,the metasilicic acid content is relatively high,which supports this conclusion.Both hydrogen and oxygen isotopes plot near the atmospheric precipitation line,indicating that groundwater recharge is functionally obtained from precipitation.The calculated thermal storage temperatures in Batang and Litang were 88–199℃ and 96–154℃,respectively.The proportion of cold water mixing in Batang was 64%–67%,while that in Litang was 60%–68%.According to the calculated results,the initial thermal cycle depth of the Batang area(4540–4780 m)was greater than that of the Litang area(3150–3960 m).The enthalpy of the deep parental geothermal fluid in Batang was 1550 J/g with a Cl^(-)concentration of 37 mg/L,while that in Litang was 2100 J/g with a Cl^(-)concentration of 48 mg/L.展开更多
The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley.The spatial distribution of the field is controlled by mountain-front fault zones on the northwe...The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley.The spatial distribution of the field is controlled by mountain-front fault zones on the northwestern and southeastern sides of the basin.Geothermal power has been generated in Yangbajain for more than 40 years.However,owing to the lack of threedimensional(3D) geophysical exploration data,key geological issues related to the partial melt body of the Yangbajain Geothermal Field,such as its location,burial depth,and geometric form,as well as the ascending channel of the geothermal fluid,have for a long time been controversial.In this study,3D inversion was performed using measured geo-electromagnetic total impedance tensor data from 47 survey points.The extracted horizontal sections at different depths and profiles,and at different lines,reflect the 3D electrical structure model of the geothermal field in the study area.Subsequently,three findings were obtained.First,the partial melt body,located below the China-Nepal Highway extending along the northeast direction,is the heat source of the Yangbajain Geothermal Field.The burial depth range of the molten body was determined to range between approximately 6.2 and 14 km.Moreover,the geothermal fluid ascended a horn-shaped circulation channel with an up-facing opening,located in the northern section of the sulfur ditch area.The study results revealed that deep rock fissures(>2 km) were not well developed and had poor permeability.In addition,no layered heat reservoirs with high water richness were observed in the northern part of the study area.However,the application of enhanced geothermal system(EGS) technology in the northern region would be essential to improving the power generation capacity of the Yangbajain Geothermal Field.In addition,the study found no deep high-temperature heat storage areas in the southern region of the study area.展开更多
We investigate the subsurface heat exchange process in EGS （enhanced geothermal systems） with a previously developed novel model. This model treats the porous heat reservoir as an equivalent porous medium of a singl...We investigate the subsurface heat exchange process in EGS （enhanced geothermal systems） with a previously developed novel model. This model treats the porous heat reservoir as an equivalent porous medium of a single porosity. However, it considers local thermal non-equilibrium between solid rock matrix and fluid flowing in the factures and employs two energy conservation equations to describe heat transfer in the rock matrix and in the fractures, respectively, enabling the modeling and analyses of convective heat exchange in the heat reservoir. Another salient feature of this model is its capability of simulating the complete subsurface heat exchange process in EGS. The EGS subsurface geometry of interest physically consists of multiple domains： open channels for injection and production wells, the artificial heat reservoir, and the rocks enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties （porosity and permeability, etc.）. This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. This model is used to perform a comprehensive parametric study with respect to an imaginary doublet EGS. Effects of several parameters, including the permeability of heat reservoir, heat exchange coefficient in the heat reservoir, the specific area of fractures in the heat reservoir, and thermal compensation from surrounding rocks, on the heat extraction efficiency and EGS lifetime are analyzed.展开更多
基金the National Key R&D Program of China(No.2019YFB1504102).
文摘Geothermal energy is a kind of renewable,sustainable and clean energy resource.Geothermal energy is abundant in carbonate reservoirs.However,low matrix permeability limits its exploitation.The super-critical carbon dioxide(SC-CO_(2))jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO_(2) simultaneously.In this paper,we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of sc-CO_(2) jet fracturing.The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface.The physical properties change of sC-CO_(2) with temperature were considered in the numerical model.Results showed that SC-CO_(2) jet frac-turing is superior to water-jet fracturing with respect to jetting velocity,particle trajectory and pene-trability.Besides,stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO_(2) jet than that by water jet.Moreover,pressure and temperature control the jet field and seepage field of sC-CO_(2) simultaneously.Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO_(2).The key findings are expected to provide a theoretical basis and design reference for applying SC-CO_(2) jet fracturing in carbonate geothermal reservoirs.
基金This work was funded by a grant from the National Natural Science Foundation of China(Grant No.41502249)Geological Survey Projects of the Chinese Geological Survey(Grant No.DD20190128)the Geological Survey Projects of the Chinese Geological Survey(Grant No.20190505).
文摘The hydrogeochemical characteristics of geothermal fluids can reveal the genesis of geothermal systems and act as important references for developing and using geothermal resources.This study presents hydrogeochemical processes and thermal cycle mechanisms of typical geothermal fields in Western Sichuan.Based on the geological conditions in Western Sichuan,29 hot springs in three geothermal fields in the Batang and Litang areas were selected for hydrochemical and isotopic(δD andδ18O)analyses.Furthermore,the temperature of the thermal reservoir was calculated and the upflow cooling process of the hot springs was analyzed.Most of the subterranean hot waters in Batang and Litang are of the HCO3-Na hydrochemical type.The ion variation in Batang is primarily affected by water-rock interactions.There is a strong positive correlation between Na+,B?,and Cl?in Litang,suggesting that they have the same material source.The Na+and metaboric acid content is relatively high,which indicates that the groundwater runoff in both areas is relatively long-lasting,with reduced flow velocity;moreover,the metasilicic acid content is relatively high,which supports this conclusion.Both hydrogen and oxygen isotopes plot near the atmospheric precipitation line,indicating that groundwater recharge is functionally obtained from precipitation.The calculated thermal storage temperatures in Batang and Litang were 88–199℃ and 96–154℃,respectively.The proportion of cold water mixing in Batang was 64%–67%,while that in Litang was 60%–68%.According to the calculated results,the initial thermal cycle depth of the Batang area(4540–4780 m)was greater than that of the Litang area(3150–3960 m).The enthalpy of the deep parental geothermal fluid in Batang was 1550 J/g with a Cl^(-)concentration of 37 mg/L,while that in Litang was 2100 J/g with a Cl^(-)concentration of 48 mg/L.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (Grant No. 2019QZKK0804)the National Natural Science Foundation of China (Grant No. U21A2015)。
文摘The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley.The spatial distribution of the field is controlled by mountain-front fault zones on the northwestern and southeastern sides of the basin.Geothermal power has been generated in Yangbajain for more than 40 years.However,owing to the lack of threedimensional(3D) geophysical exploration data,key geological issues related to the partial melt body of the Yangbajain Geothermal Field,such as its location,burial depth,and geometric form,as well as the ascending channel of the geothermal fluid,have for a long time been controversial.In this study,3D inversion was performed using measured geo-electromagnetic total impedance tensor data from 47 survey points.The extracted horizontal sections at different depths and profiles,and at different lines,reflect the 3D electrical structure model of the geothermal field in the study area.Subsequently,three findings were obtained.First,the partial melt body,located below the China-Nepal Highway extending along the northeast direction,is the heat source of the Yangbajain Geothermal Field.The burial depth range of the molten body was determined to range between approximately 6.2 and 14 km.Moreover,the geothermal fluid ascended a horn-shaped circulation channel with an up-facing opening,located in the northern section of the sulfur ditch area.The study results revealed that deep rock fissures(>2 km) were not well developed and had poor permeability.In addition,no layered heat reservoirs with high water richness were observed in the northern part of the study area.However,the application of enhanced geothermal system(EGS) technology in the northern region would be essential to improving the power generation capacity of the Yangbajain Geothermal Field.In addition,the study found no deep high-temperature heat storage areas in the southern region of the study area.
文摘We investigate the subsurface heat exchange process in EGS （enhanced geothermal systems） with a previously developed novel model. This model treats the porous heat reservoir as an equivalent porous medium of a single porosity. However, it considers local thermal non-equilibrium between solid rock matrix and fluid flowing in the factures and employs two energy conservation equations to describe heat transfer in the rock matrix and in the fractures, respectively, enabling the modeling and analyses of convective heat exchange in the heat reservoir. Another salient feature of this model is its capability of simulating the complete subsurface heat exchange process in EGS. The EGS subsurface geometry of interest physically consists of multiple domains： open channels for injection and production wells, the artificial heat reservoir, and the rocks enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties （porosity and permeability, etc.）. This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. This model is used to perform a comprehensive parametric study with respect to an imaginary doublet EGS. Effects of several parameters, including the permeability of heat reservoir, heat exchange coefficient in the heat reservoir, the specific area of fractures in the heat reservoir, and thermal compensation from surrounding rocks, on the heat extraction efficiency and EGS lifetime are analyzed.
