Shale samples of Silurian Longmaxi Formation in the Changning area of the Sichuan Basin, SW China, were selected to carry out scanning electron microscopy, CT imaging, high-pressure mercury injection, low-temperature ...Shale samples of Silurian Longmaxi Formation in the Changning area of the Sichuan Basin, SW China, were selected to carry out scanning electron microscopy, CT imaging, high-pressure mercury injection, low-temperature nitrogen adsorption and imbibition experiments to compare the hydration characteristics of montmorillonite and illite, analyze the main factors affecting the water block removal of shale, and reveal the mechanisms of pore structure evolution during shale hydration. The hydration characteristics of shale are closely related to the composition of clay minerals, the shale with high illite content is not susceptible to hydration and thus has limited room for pore structure improvement;the shale with high montmorillonite is susceptible to hydration expansion and thus has higher potential of pore structure improvement by stimulation;the shale with high illite content has stronger imbibition in the initial stage, but insufficient diffusion ability, and thus is likely to have water block;the shale with high montmorillonite content has weaker imbibition in the initial stage but better water diffusion, so water blocking in this kind of shale can be removed to some degree;the shale reservoir has an optimal hydration time, when it is best in physical properties, but hydration time too long would cause damage to the reservoir, and the shale with high illite content has a shorter optimal hydration time;inorganic cations can inhibit the hydration of clay minerals and have stronger inhibition to illite expansion, especially K^(+);for the reservoir with high content of montmorillonite, the cation content of fracturing fluid can be lowered to promote the shale hydration;fracturing fluid with high K^(+) content can be injected into reservoirs with high illite content to suppress hydration.展开更多
Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element（REE） data for surface sediments collected from the...Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element（REE） data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component.Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust（UCC） in SiO_2, Al_2O_3, CaO, MgO, alkali elements（Rb, Cs） and high field strength elements（Nb, Ta, Zr, Hf, Ti）. These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction（~55%–60%） are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.展开更多
The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is model...The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications.In this paper,a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias.Using this plasma density distribution as the initial condition,a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time.The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field.The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24,respectively,of which the value is 1 at the central plasma source.After a 5μs pulse-on time,in the area less than 2 cm from the end of the tube,the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°;both variations reduce the nitrogen ion implantation depth.However,the nitrogen ion implantation dose peaks of about 2×10^（10）-7×10^（10）ions/cm^2 in this area are 2-4 times higher than that of 1.18×10^（10）ions/cm^2 and 1.63×10^（10）ions/cm^2 on the inner and outer surfaces of the tube.The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation,because the modification effect is mainly determined by the ion implantation dose,just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion.Therefore,a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.展开更多
This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distr...This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data underdifferent confining pressures for stress-driven fractures and under different water injection conditions for fluiddriven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process,2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3)extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupturevelocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEschanges from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershockactivity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 m2/s to10–100 m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating thathydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuringthe safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparationprocess for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected tobe used for various purposes, including 1) as training data for artificial intelligence related to microseismic dataprocessing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models andassessment methods for the relationship between microseismic characteristics and rock hydraulic properties,which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.展开更多
Simulation of the mixing mechanism of submerged multiport diffusers used to discharge heated water from thermal-electric power plants and households into shallow receiving waters was described. The three-dimensional t...Simulation of the mixing mechanism of submerged multiport diffusers used to discharge heated water from thermal-electric power plants and households into shallow receiving waters was described. The three-dimensional turbulence model and hybrid finite analytic method were used to predict the behavior of near field for multiport buoyant jets in rivers. The predicted temperature dilution and velocity prove good by comparison with available laboratory measurements. An empirical formula for temperature dilution and velocity in near field for this kind of flow was given. The effect of parameters on the dilution behavior of multiple jets were also discussed.展开更多
The k-Ε turbulence model was used to establish the mathematical model of two-dimensional line buoyant jets in crossflow. The hybrid finite analytic method and staggered grid were applied to the calculation of line bu...The k-Ε turbulence model was used to establish the mathematical model of two-dimensional line buoyant jets in crossflow. The hybrid finite analytic method and staggered grid were applied to the calculation of line buoyant jets. Only receiving water with uniform density is considered. The distribution of velocity, temperature and turbulent kinetic energy were analyzed, and the variation of the maximum velocity was given. The effect of velocity ratio and densimetric Froude number on line buoyant jets was considered.展开更多
Understanding the hydraulic and frictional sensitivity of fault to different injection conditions is one of the efficient ways to provide useful implications for fault reactivation potential.Numerical simulations of f...Understanding the hydraulic and frictional sensitivity of fault to different injection conditions is one of the efficient ways to provide useful implications for fault reactivation potential.Numerical simulations of fractured reservoir have provided information on how fault behaviour varies under changing hydromechanical properties and injection conditions.A coupled hydro-mechanical model which can represent the elastoplastic behaviour of a fault was employed to predict and quantify the effects of varying injection positions and injection rates on permeability response and potential of fault reactivation under isothermal injection.We examine the sensitivity of seismic event magnitude and timing to variations in both pressure perturbation and stress as injection location changes.We generate results for two scenarios:one with changing injection position but with uniform injection rate,and another scenario with increasing injection rate at the same injection position.We observed that the potential of fault reactivation is affected by the hydraulic diffusivity potential of the fluid pressure,and this mechanism is mediated by a function of the injector position and injection rate.As the velocity of fluid transmission increases,increasing fluid pressure impact pore pressure elevation and reduced effective stress.However,an injector position where there is low diffusivity causes low pore pressure build-up rate,incapable of inducing shear failure,and thus,permeability enhancement is retarded in this case.Accordingly,the injection rate variation influences the rate of pore pressure build-up,the timing and magnitude of induced seismic events.This is also reflected in the permeability evolution as a response to the variations in the magnitude of fault openings and cracks.This changing injection conditions however influences the timing required to reach the critical peak friction point as pore pressure build-up rate and sensitivity to loading response change.Hence,with changing position and rate of injection,the evolution of fault permeability appears to be intrinsically controlled by a condition which favours elastoplastic deformation and fracture failure,with slip distance increasing with high injection rates.展开更多
We present a new Dirichlet boundary condition for the rate-type non-Newtonian diffusive constitutive models. The newly proposed boundary condition is compared with two such well-known and popularly used boundary condi...We present a new Dirichlet boundary condition for the rate-type non-Newtonian diffusive constitutive models. The newly proposed boundary condition is compared with two such well-known and popularly used boundary conditions as the pure Neumann condition and the Dirichlet condition by Sureshkumar and Beris. Our condition is demonstrated to be more stable and robust in a number of numerical test cases. A new Dirichlet boundary condition is implemented in the framework of the finite difference Marker and Cell （MAC） method. In this paper, we also present an energy-stable finite difference MAC scheme that preserves the positivity for the conformation tensor and show how the addition of the diffusion helps the energy-stability in a finite difference MAC scheme-setting.展开更多
基金Supported by the Science and Technology Planning Project of Sichuan Province,China(2020YJ0135)National Natural Science Foundation of China(51874250)。
文摘Shale samples of Silurian Longmaxi Formation in the Changning area of the Sichuan Basin, SW China, were selected to carry out scanning electron microscopy, CT imaging, high-pressure mercury injection, low-temperature nitrogen adsorption and imbibition experiments to compare the hydration characteristics of montmorillonite and illite, analyze the main factors affecting the water block removal of shale, and reveal the mechanisms of pore structure evolution during shale hydration. The hydration characteristics of shale are closely related to the composition of clay minerals, the shale with high illite content is not susceptible to hydration and thus has limited room for pore structure improvement;the shale with high montmorillonite is susceptible to hydration expansion and thus has higher potential of pore structure improvement by stimulation;the shale with high illite content has stronger imbibition in the initial stage, but insufficient diffusion ability, and thus is likely to have water block;the shale with high montmorillonite content has weaker imbibition in the initial stage but better water diffusion, so water blocking in this kind of shale can be removed to some degree;the shale reservoir has an optimal hydration time, when it is best in physical properties, but hydration time too long would cause damage to the reservoir, and the shale with high illite content has a shorter optimal hydration time;inorganic cations can inhibit the hydration of clay minerals and have stronger inhibition to illite expansion, especially K^(+);for the reservoir with high content of montmorillonite, the cation content of fracturing fluid can be lowered to promote the shale hydration;fracturing fluid with high K^(+) content can be injected into reservoirs with high illite content to suppress hydration.
基金The National Key Basic Research Program of China under contract Nos 2013CB429705 and 2013CB429701the National Natural Science Foundation of China under contract Nos 41176045 and 41376067+1 种基金the Scientific Research Fund of the Second Institute of Oceanographythe SOA of China under contract Nos JG1403 and JT1304
文摘Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element（REE） data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component.Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust（UCC） in SiO_2, Al_2O_3, CaO, MgO, alkali elements（Rb, Cs） and high field strength elements（Nb, Ta, Zr, Hf, Ti）. These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction（~55%–60%） are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.
基金supported by National Natural Science Foundation of China(Nos.50725519,51271048,51321004)
文摘The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications.In this paper,a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias.Using this plasma density distribution as the initial condition,a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time.The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field.The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24,respectively,of which the value is 1 at the central plasma source.After a 5μs pulse-on time,in the area less than 2 cm from the end of the tube,the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°;both variations reduce the nitrogen ion implantation depth.However,the nitrogen ion implantation dose peaks of about 2×10^（10）-7×10^（10）ions/cm^2 in this area are 2-4 times higher than that of 1.18×10^（10）ions/cm^2 and 1.63×10^（10）ions/cm^2 on the inner and outer surfaces of the tube.The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation,because the modification effect is mainly determined by the ion implantation dose,just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion.Therefore,a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.
文摘This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data underdifferent confining pressures for stress-driven fractures and under different water injection conditions for fluiddriven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process,2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3)extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupturevelocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEschanges from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershockactivity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 m2/s to10–100 m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating thathydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuringthe safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparationprocess for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected tobe used for various purposes, including 1) as training data for artificial intelligence related to microseismic dataprocessing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models andassessment methods for the relationship between microseismic characteristics and rock hydraulic properties,which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.
文摘Simulation of the mixing mechanism of submerged multiport diffusers used to discharge heated water from thermal-electric power plants and households into shallow receiving waters was described. The three-dimensional turbulence model and hybrid finite analytic method were used to predict the behavior of near field for multiport buoyant jets in rivers. The predicted temperature dilution and velocity prove good by comparison with available laboratory measurements. An empirical formula for temperature dilution and velocity in near field for this kind of flow was given. The effect of parameters on the dilution behavior of multiple jets were also discussed.
文摘The k-Ε turbulence model was used to establish the mathematical model of two-dimensional line buoyant jets in crossflow. The hybrid finite analytic method and staggered grid were applied to the calculation of line buoyant jets. Only receiving water with uniform density is considered. The distribution of velocity, temperature and turbulent kinetic energy were analyzed, and the variation of the maximum velocity was given. The effect of velocity ratio and densimetric Froude number on line buoyant jets was considered.
文摘Understanding the hydraulic and frictional sensitivity of fault to different injection conditions is one of the efficient ways to provide useful implications for fault reactivation potential.Numerical simulations of fractured reservoir have provided information on how fault behaviour varies under changing hydromechanical properties and injection conditions.A coupled hydro-mechanical model which can represent the elastoplastic behaviour of a fault was employed to predict and quantify the effects of varying injection positions and injection rates on permeability response and potential of fault reactivation under isothermal injection.We examine the sensitivity of seismic event magnitude and timing to variations in both pressure perturbation and stress as injection location changes.We generate results for two scenarios:one with changing injection position but with uniform injection rate,and another scenario with increasing injection rate at the same injection position.We observed that the potential of fault reactivation is affected by the hydraulic diffusivity potential of the fluid pressure,and this mechanism is mediated by a function of the injector position and injection rate.As the velocity of fluid transmission increases,increasing fluid pressure impact pore pressure elevation and reduced effective stress.However,an injector position where there is low diffusivity causes low pore pressure build-up rate,incapable of inducing shear failure,and thus,permeability enhancement is retarded in this case.Accordingly,the injection rate variation influences the rate of pore pressure build-up,the timing and magnitude of induced seismic events.This is also reflected in the permeability evolution as a response to the variations in the magnitude of fault openings and cracks.This changing injection conditions however influences the timing required to reach the critical peak friction point as pore pressure build-up rate and sensitivity to loading response change.Hence,with changing position and rate of injection,the evolution of fault permeability appears to be intrinsically controlled by a condition which favours elastoplastic deformation and fracture failure,with slip distance increasing with high injection rates.
文摘We present a new Dirichlet boundary condition for the rate-type non-Newtonian diffusive constitutive models. The newly proposed boundary condition is compared with two such well-known and popularly used boundary conditions as the pure Neumann condition and the Dirichlet condition by Sureshkumar and Beris. Our condition is demonstrated to be more stable and robust in a number of numerical test cases. A new Dirichlet boundary condition is implemented in the framework of the finite difference Marker and Cell （MAC） method. In this paper, we also present an energy-stable finite difference MAC scheme that preserves the positivity for the conformation tensor and show how the addition of the diffusion helps the energy-stability in a finite difference MAC scheme-setting.
