In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels...In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.展开更多
In the Southeastern Sichuan Basin,the deep shale reservoirs(with vertical depth over 2800 m)are complicated and diverse in reservoir mineral compositions and pore structural characteristics,with the obvious rock plast...In the Southeastern Sichuan Basin,the deep shale reservoirs(with vertical depth over 2800 m)are complicated and diverse in reservoir mineral compositions and pore structural characteristics,with the obvious rock plasticity and nonlinear fracturing features and the high absolute difference between maximum and minimum principal stresses,due to the effect of geological setting and diagenesis.Consequently,staged fracturing operations often suffer from high fracturing pressure and propagating pressure,small fracture width,low sandefluid ratio and fracture conductivity and difficult formation of volume fractures,which seriously influence the post-fracturing shale gas productivity.In this paper,a new combined fracturing mode(pretreatment acid+gelled fluid+slickwater+gelled fluid)and its supporting technologies were developed after a series of analysis and studies on deep rocks in terms of mechanical property,earth stress characteristics,fracturing characteristics and fracture morphology characteristics.Field application shows that geologic breakthrough was realized in Longmaxi Fm of Lower Silurian in Well Dingye 2HF,with absolute open flow(AOF)of 10.5×10^(4)m^(3)/d after fracturing.And it was expected to reach commercial breakthrough in Qiongzhusi Fm of Lower Cambrian in Well Jinye 1HF,with AOF of 10.5×10^(4)m^(3)/d after fracturing.Finally,the following conclusions are reached.First,it is hard to form complex fractures in deep shale and the fracturing technologies applicable for it should be different from those used in midedeep zones.Second,the established fracturing pressure model can provide an effective way for deep-zone fracturing pressure prediction.Third,reducing operation pressure is one of the key measures to ensure successful deep-zone fracturing.Fourth,besides good material basis,it is crucial to increase the complexity of induced fractures and generate high-conductivity fractures in order to guarantee successful fracturing in deep shale.展开更多
A better placement of proppants has been always the goal pursued in sand fracturing in order to get longer effective fractures and higher flow conductivity.However,it is always difficult to achieve satisfactory effect...A better placement of proppants has been always the goal pursued in sand fracturing in order to get longer effective fractures and higher flow conductivity.However,it is always difficult to achieve satisfactory effects by conventional processes.On the basis of theoretical analysis and simulation with FracproPT software,basic experiments,and innovative physical modeling experiment,a new impulse-stage fracturing process has been developed by combining a special pumping process with fiber,liquid and other auxiliary engineering means.Compared with conventional fracturing,the open seepage channel created by the new fracturing process has an obvious edge in effective fracture length and flow conductivity.Moreover,the open seepage channel can also improve fracture cleanliness and reduce pressure loss in artificial fractures,thus reaching the goal of prolonging the single-well production time and maximizing productivity.After the research on principles and optimal design of this new process,on-site pilot test and detailed post-fracturing evaluation were conducted.The results indicated that(1)the new process is highly operable and feasible;(2)compared with the adjacent wells with similar geological conditions,the proppant'cost is reduced by 44%-47%,the ratio of effective fracture length to propped fracture length is increased by about 16%,the fracturing fluid recovery rate is up to 63%after 18 h in the test,and the normalized production is 1.9-2.3 times that of the adjacent wells;and(3)the new process can significantly lower the cost and enhance production.The process has a broad application prospect in shallow-middle sand gas reservoirs and shale gas reservoirs in western Sichuan Basin.展开更多
The transpiration rate of plant is physically controlled by the magnitude of the vapor pressure deficit（VPD） and stomatal conductance. A limited-transpiration trait has been reported for many crop species in differe...The transpiration rate of plant is physically controlled by the magnitude of the vapor pressure deficit（VPD） and stomatal conductance. A limited-transpiration trait has been reported for many crop species in different environments, including Maize（Zea mays L.）. This trait results in restricted transpiration rate under high VPD, and can potentially conserve soil water and thus decrease soil water deficit. However, such a restriction on transpiration rate has never been explored in maize under arid climatic conditions in northwestern China. The objective of this study was to examine the transpiration rate of field-grown maize under well-watered conditions in an arid area at both leaf and whole plant levels, and therefore to investigate how transpiration rate responding to the ambient VPD at different spatial and temporal scales. The transpiration rates of maize at leaf and plant scales were measured independently using a gas exchange system and sapflow instrument, respectively. Results showed significant variations in transpiration responses of maize to VPD among different spatio-temporal scales. A two-phase transpiration response was observed at leaf level with a threshold of 3.5 k Pa while at the whole plant level, the daytime transpiration rate was positively associated with VPD across all measurement data, as was nighttime transpiration response to VPD at both leaf and whole plant level, which showed no definable threshold vapor pressure deficit, above which transpiration rate was restricted. With regard to temporal scale, transpiration was most responsive to VPD at a daily scale, moderately responsive at a half-hourly scale, and least responsive at an instantaneous scale. A similar breakpoint（about 3.0 k Pa） in response of the instantaneous leaf stomatal conductance and hourly canopy bulk conductance to VPD were also observed. At a daily scale, the maximum canopy bulk conductance occurred at a VPD about 1.7 k Pa. Generally, the responsiveness of stomatal conductance to VPD at the canopy scale was lower than that at leaf scale. These results indicate a temporal and spatial heterogeneity in how maize transpiration responses to VPD under arid climatic conditions. This could allow a better assessment of the possible benefits of using the maximum transpiration trait to improve maize drought tolerance in arid environment, and allow a better prediction of plant transpiration which underpin empirical models for stomatal conductance at different spatio-temporal scales in the arid climatic conditions.展开更多
Even though a large number of large-scale arch dams with height larger than 200 m have been built in the world, the transient groundwater flow behaviors and the seepage control effects in the dam foundations under dif...Even though a large number of large-scale arch dams with height larger than 200 m have been built in the world, the transient groundwater flow behaviors and the seepage control effects in the dam foundations under difficult geological conditions are rarely reported. This paper presents a case study on the transient groundwater flow behaviors in the rock foundation of Jinping I double-curvature arch dam, the world＇s highest dam of this type to date that has been completed. Taking into account the geological settings at the site, an inverse modeling technique utilizing the time series measurements of both hydraulic head and discharge was adopted to back-calculate the permeability of the foundation rocks,which effectively improves the uniqueness and reliability of the inverse modeling results. The transient seepage flow in the dam foundation during the reservoir impounding was then modeled with a parabolic variational inequality（PVI） method. The distribution of pore water pressure, the amount of leakage, and the performance of the seepage control system in the dam foundation during the entire impounding process were finally illustrated with the numerical results.展开更多
Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical sol...Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume(SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.展开更多
We have explored the structure of a hot flow bathed in a general large-scale magnetic field. The importance of outflow and thermal conduction on the self-similar structure of a hot accretion flow has been investigated...We have explored the structure of a hot flow bathed in a general large-scale magnetic field. The importance of outflow and thermal conduction on the self-similar structure of a hot accretion flow has been investigated. We consider the additional 2 2 2 magnetic parameters are the Alfv6n sound speeds in three directions of cylindrical coordinates. In comparison to the accretion disk without winds, our results show that the radial and rotational velocities of the disk become faster, but the disk becomes cooler because of the angular momentum and energy flux which are taken away by the winds. Moreover, thermal conduction opposes the effect of winds and not only decreases the rotational velocity but also in- creases the radial velocity as well as the sound speed of the disk. In addition, we study the effect of the global magnetic field on the structure of the disk. Our numerical re- suits show that all the components of a magnetic field can be important and they have a considerable effect on velocities and vertical structure of the disk.展开更多
The western Sichuan hydrothermal area is located at the northeastern margin of the eastern syntaxis of the Qinghai-Tibet Plateau, which is also the eastern end of the Mediterranean-Himalayan geothermal activity zone. ...The western Sichuan hydrothermal area is located at the northeastern margin of the eastern syntaxis of the Qinghai-Tibet Plateau, which is also the eastern end of the Mediterranean-Himalayan geothermal activity zone. There are 248 warm or hot springs in this area, and 11 have temperatures beyond the local boiling temperature. Most of these hot springs are distributed along the Jinshajiang, Dege-Xiangcheng, Ganzi-Litang, and Xianshuihe faults, forming a NW-SE hydrothermal belt. A geothermal analysis of this high-temperature hydrothermal area is an important basis for understanding the deep geodynamic process of the eastern syntaxis of the Qinghai-Tibet Plateau. In addition, this study offers an a priori view to utilize geothermal resources, which is important in both scientific research and application. We use gravity, magnetic, seismic, and helium isotope data to analyze the crust-mantle heat flow ratio and deep geothermal structure. The results show that the background terrestrial heat flow descends from southwest to northeast. The crustal heat ratio is not more than 60%. The high temperature hydrothermal active is related to crustal dynamics processes. Along the Batang-Litang-Kangding line, the Moho depth increases eastward, which is consistent with the changing Qc/Qm(crustal/mantle heat flow) ratio trend. The geoid in the hydrothermal zone is 4–6 km higher than the surroundings, forming a local "platform". The NW-SE striking local tensile stress zone and uplift structure in the upper and middle crust corresponds with the surface hydrothermal active zone. There is an average Curie Point Depth(CPD) of 19.5–22.5 km in Batang, Litang, and Kangding. The local shear-wave(S-wave) velocity is relatively low in the middle and lower crust. The S-wave shows a low velocity trap(Vs<3.2 km s.1) at 15–30 km, which is considered a high-temperature partial melting magma, the crustal source of the hydrothermal active zone. We conclude that the hydrothermal system in this area can be divided into Batang-type and Kangding-type, both of which rely on a crustal heating cycle of atmospheric precipitation and surface water along the fracture zone. The heat is derived from the middle and lower crust: groundwater penetrates the deep faults bringing geothermal energy back to the surface and forming high-temperature springs.展开更多
基金This work was financially supported by the National Natural Science Foundation of China(No.52074041)the Chongqing Talent Program(No.cstc2022ycjh-bgzxm0077)the Postgraduate Research and Innovation Foundation of Chongqing,China(No.CYS23060).
文摘In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.
基金Project supported by Sinopec Science and Technology Project“Optimized stimulation of shale gas zones in Fuling block”(Grant No.P14091).
文摘In the Southeastern Sichuan Basin,the deep shale reservoirs(with vertical depth over 2800 m)are complicated and diverse in reservoir mineral compositions and pore structural characteristics,with the obvious rock plasticity and nonlinear fracturing features and the high absolute difference between maximum and minimum principal stresses,due to the effect of geological setting and diagenesis.Consequently,staged fracturing operations often suffer from high fracturing pressure and propagating pressure,small fracture width,low sandefluid ratio and fracture conductivity and difficult formation of volume fractures,which seriously influence the post-fracturing shale gas productivity.In this paper,a new combined fracturing mode(pretreatment acid+gelled fluid+slickwater+gelled fluid)and its supporting technologies were developed after a series of analysis and studies on deep rocks in terms of mechanical property,earth stress characteristics,fracturing characteristics and fracture morphology characteristics.Field application shows that geologic breakthrough was realized in Longmaxi Fm of Lower Silurian in Well Dingye 2HF,with absolute open flow(AOF)of 10.5×10^(4)m^(3)/d after fracturing.And it was expected to reach commercial breakthrough in Qiongzhusi Fm of Lower Cambrian in Well Jinye 1HF,with AOF of 10.5×10^(4)m^(3)/d after fracturing.Finally,the following conclusions are reached.First,it is hard to form complex fractures in deep shale and the fracturing technologies applicable for it should be different from those used in midedeep zones.Second,the established fracturing pressure model can provide an effective way for deep-zone fracturing pressure prediction.Third,reducing operation pressure is one of the key measures to ensure successful deep-zone fracturing.Fourth,besides good material basis,it is crucial to increase the complexity of induced fractures and generate high-conductivity fractures in order to guarantee successful fracturing in deep shale.
文摘A better placement of proppants has been always the goal pursued in sand fracturing in order to get longer effective fractures and higher flow conductivity.However,it is always difficult to achieve satisfactory effects by conventional processes.On the basis of theoretical analysis and simulation with FracproPT software,basic experiments,and innovative physical modeling experiment,a new impulse-stage fracturing process has been developed by combining a special pumping process with fiber,liquid and other auxiliary engineering means.Compared with conventional fracturing,the open seepage channel created by the new fracturing process has an obvious edge in effective fracture length and flow conductivity.Moreover,the open seepage channel can also improve fracture cleanliness and reduce pressure loss in artificial fractures,thus reaching the goal of prolonging the single-well production time and maximizing productivity.After the research on principles and optimal design of this new process,on-site pilot test and detailed post-fracturing evaluation were conducted.The results indicated that(1)the new process is highly operable and feasible;(2)compared with the adjacent wells with similar geological conditions,the proppant'cost is reduced by 44%-47%,the ratio of effective fracture length to propped fracture length is increased by about 16%,the fracturing fluid recovery rate is up to 63%after 18 h in the test,and the normalized production is 1.9-2.3 times that of the adjacent wells;and(3)the new process can significantly lower the cost and enhance production.The process has a broad application prospect in shallow-middle sand gas reservoirs and shale gas reservoirs in western Sichuan Basin.
基金funded by the National Science Fund for Distinguished Young Scholars (41125002)the Chinese National Natural Science Foundation (41271036)
文摘The transpiration rate of plant is physically controlled by the magnitude of the vapor pressure deficit（VPD） and stomatal conductance. A limited-transpiration trait has been reported for many crop species in different environments, including Maize（Zea mays L.）. This trait results in restricted transpiration rate under high VPD, and can potentially conserve soil water and thus decrease soil water deficit. However, such a restriction on transpiration rate has never been explored in maize under arid climatic conditions in northwestern China. The objective of this study was to examine the transpiration rate of field-grown maize under well-watered conditions in an arid area at both leaf and whole plant levels, and therefore to investigate how transpiration rate responding to the ambient VPD at different spatial and temporal scales. The transpiration rates of maize at leaf and plant scales were measured independently using a gas exchange system and sapflow instrument, respectively. Results showed significant variations in transpiration responses of maize to VPD among different spatio-temporal scales. A two-phase transpiration response was observed at leaf level with a threshold of 3.5 k Pa while at the whole plant level, the daytime transpiration rate was positively associated with VPD across all measurement data, as was nighttime transpiration response to VPD at both leaf and whole plant level, which showed no definable threshold vapor pressure deficit, above which transpiration rate was restricted. With regard to temporal scale, transpiration was most responsive to VPD at a daily scale, moderately responsive at a half-hourly scale, and least responsive at an instantaneous scale. A similar breakpoint（about 3.0 k Pa） in response of the instantaneous leaf stomatal conductance and hourly canopy bulk conductance to VPD were also observed. At a daily scale, the maximum canopy bulk conductance occurred at a VPD about 1.7 k Pa. Generally, the responsiveness of stomatal conductance to VPD at the canopy scale was lower than that at leaf scale. These results indicate a temporal and spatial heterogeneity in how maize transpiration responses to VPD under arid climatic conditions. This could allow a better assessment of the possible benefits of using the maximum transpiration trait to improve maize drought tolerance in arid environment, and allow a better prediction of plant transpiration which underpin empirical models for stomatal conductance at different spatio-temporal scales in the arid climatic conditions.
基金financially supported through NSERC Discovery Grant(RGPIN/4994-2014)
文摘Even though a large number of large-scale arch dams with height larger than 200 m have been built in the world, the transient groundwater flow behaviors and the seepage control effects in the dam foundations under difficult geological conditions are rarely reported. This paper presents a case study on the transient groundwater flow behaviors in the rock foundation of Jinping I double-curvature arch dam, the world＇s highest dam of this type to date that has been completed. Taking into account the geological settings at the site, an inverse modeling technique utilizing the time series measurements of both hydraulic head and discharge was adopted to back-calculate the permeability of the foundation rocks,which effectively improves the uniqueness and reliability of the inverse modeling results. The transient seepage flow in the dam foundation during the reservoir impounding was then modeled with a parabolic variational inequality（PVI） method. The distribution of pore water pressure, the amount of leakage, and the performance of the seepage control system in the dam foundation during the entire impounding process were finally illustrated with the numerical results.
基金Project(2011ZX05015)supported by Important National Science and Technology Specific Projects of the "Twelfth Five-years" Plan Period,China
文摘Multiple fractured horizontal well(MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume(SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.
文摘We have explored the structure of a hot flow bathed in a general large-scale magnetic field. The importance of outflow and thermal conduction on the self-similar structure of a hot accretion flow has been investigated. We consider the additional 2 2 2 magnetic parameters are the Alfv6n sound speeds in three directions of cylindrical coordinates. In comparison to the accretion disk without winds, our results show that the radial and rotational velocities of the disk become faster, but the disk becomes cooler because of the angular momentum and energy flux which are taken away by the winds. Moreover, thermal conduction opposes the effect of winds and not only decreases the rotational velocity but also in- creases the radial velocity as well as the sound speed of the disk. In addition, we study the effect of the global magnetic field on the structure of the disk. Our numerical re- suits show that all the components of a magnetic field can be important and they have a considerable effect on velocities and vertical structure of the disk.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41574074, 41174085, 41430319)the Innovation Team Project of Chinese Academy of Sciences (Grant No. KZZD-EW-TZ-19)the Strategic Pilot Technology of Chinese Academy of Sciences (Grant No. XDA1103010102)
文摘The western Sichuan hydrothermal area is located at the northeastern margin of the eastern syntaxis of the Qinghai-Tibet Plateau, which is also the eastern end of the Mediterranean-Himalayan geothermal activity zone. There are 248 warm or hot springs in this area, and 11 have temperatures beyond the local boiling temperature. Most of these hot springs are distributed along the Jinshajiang, Dege-Xiangcheng, Ganzi-Litang, and Xianshuihe faults, forming a NW-SE hydrothermal belt. A geothermal analysis of this high-temperature hydrothermal area is an important basis for understanding the deep geodynamic process of the eastern syntaxis of the Qinghai-Tibet Plateau. In addition, this study offers an a priori view to utilize geothermal resources, which is important in both scientific research and application. We use gravity, magnetic, seismic, and helium isotope data to analyze the crust-mantle heat flow ratio and deep geothermal structure. The results show that the background terrestrial heat flow descends from southwest to northeast. The crustal heat ratio is not more than 60%. The high temperature hydrothermal active is related to crustal dynamics processes. Along the Batang-Litang-Kangding line, the Moho depth increases eastward, which is consistent with the changing Qc/Qm(crustal/mantle heat flow) ratio trend. The geoid in the hydrothermal zone is 4–6 km higher than the surroundings, forming a local "platform". The NW-SE striking local tensile stress zone and uplift structure in the upper and middle crust corresponds with the surface hydrothermal active zone. There is an average Curie Point Depth(CPD) of 19.5–22.5 km in Batang, Litang, and Kangding. The local shear-wave(S-wave) velocity is relatively low in the middle and lower crust. The S-wave shows a low velocity trap(Vs<3.2 km s.1) at 15–30 km, which is considered a high-temperature partial melting magma, the crustal source of the hydrothermal active zone. We conclude that the hydrothermal system in this area can be divided into Batang-type and Kangding-type, both of which rely on a crustal heating cycle of atmospheric precipitation and surface water along the fracture zone. The heat is derived from the middle and lower crust: groundwater penetrates the deep faults bringing geothermal energy back to the surface and forming high-temperature springs.
