Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of ...Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.展开更多
With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,sha...With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,shale oil and gas reservoirs have become the focus of unconventional oil and gas resources exploration and development.Based on the characteristics of shale oil and gas reservoirs,supercritical CO_(2) fracturing is more conducive to improving oil recovery than other fracturing technologies.In this paper,the mechanism of fracture initiation and propagation of supercritical CO_(2) in shale is analyzed,including viscosity effect,surface tension effect,permeation diffusion effect of supercritical CO_(2),and dissolution-adsorption effect between CO_(2) and shale.The effects of natural factors,such as shale properties,bedding plane and natural fractures,and controllable factors,proppant,temperature,pressure,CO_(2) concentration and injection rate on fracture initiation and propagation are clarified.The methods of supercritical CO_(2) fracturing process,thickener and proppant optimization to improve the efficiency of supercritical CO_(2) fracturing are discussed.In addition,some new technologies of supercritical CO_(2) fracturing are introduced.The challenges and prospects in the current research are also summarized.For example,supercritical CO_(2) is prone to filtration when passing through porous media,and it is difficult to form a stable flow state.Therefore,in order to achieve stable fracturing fluid suspension and effectively support fractu res,it is urge nt to explo re new fracturing fluid additives or improve fracturing fluid formulations combined with the research of new proppants.This paper is of great significance for understanding the behavior mechanism of supercritical CO_(2) in shale and optimizing fracturing technology.展开更多
We consider the multiplicity of solutions to a p(x)-Laplacian problem involving supercritical Sobolev growth via Ricceri’s principle.By means of truncation combined with De Giorgi iteration,we can extend the results ...We consider the multiplicity of solutions to a p(x)-Laplacian problem involving supercritical Sobolev growth via Ricceri’s principle.By means of truncation combined with De Giorgi iteration,we can extend the results of subcritical and critical growth to supercritical growth and obtain at least three solutions to the p(x)-Laplacian problem.展开更多
Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrol...Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale.The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared.The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified.The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction,and gradually increased with increasing time.The prediction error can reach less than 25%when the reaction time was 12 h.The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas,and its prediction error is less than 14%in this paper.The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon,asphaltene pyrolysis generates saturated hydrocarbon,aromatic hydrocarbon and resin,saturated hydrocarbon,aromatic hydrocarbon and resin polymerization generates asphaltene,and saturated hydrocarbon,resin and asphaltene generates gas.The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene.展开更多
Understanding the solubility of supercritical CO_(2)and its mixtures with other fluids at various temperatures and pressures conditions is critical for their applications,such as extraction processes,material design,a...Understanding the solubility of supercritical CO_(2)and its mixtures with other fluids at various temperatures and pressures conditions is critical for their applications,such as extraction processes,material design,and carbon capture.In the present study,the solubility parameters of supercritical CO_(2),H_(2)O,and their mixtures were calculated by molecular dynamics simulations.The results show that the solubility parameters decrease with increasing temperature and increase with increasing pressure and are linearly proportional to the density.Furthermore,the intermolecular interactions,including the hydrogen bonds,significantly affect the solubility parameter of the CO_(2)-H_(2)O system.展开更多
Aviation kerosene RP-3 is extensively used in China.This paper details the measurement of the density of Chinese aviation kerosene RP-3 employing the flow method under high-pressure and high-temperature conditions.The...Aviation kerosene RP-3 is extensively used in China.This paper details the measurement of the density of Chinese aviation kerosene RP-3 employing the flow method under high-pressure and high-temperature conditions.The methodology utilizes circular tubes with two different diameters.The density of aviation kerosene RP-3 was experimentally measured for the first time within a pressure range from 6 MPa to 8 MPa and a temperature range from 323 K to 783 K,with a maximum relative uncertainty of 0.35%.The experimental setup used n-decane for calibration,achieving an average calibration error of 0.91%.The data indicate that the density of RP-3 ranges from 764 kg/m^(3)to 247 kg/m^(3)under the tested conditions.The results show that the density of kerosene RP-3 decreases with an increase in temperature at a constant pressure,and at a given temperature,a higher pressure results in a higher density.Polynomial fitting was applied to the data,resulting in the average absolute deviation of 1.09%,0.80%,and 0.76%at different pressures of 6,7,and 8 MPa,respectively.展开更多
In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential f...In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential for enhancing the performance of such systems.This study examines the main sCO_(2) compressor from Sandia Laboratory,utilizing entropy production theory to elucidate the sources and distribution of energy losses both across the entire machine and within its key flow components.The findings reveal that turbulent viscous dissipation is the predominant contributor to total entropy production.Interestingly,while the relative importance of the entropy produced by various sources as the mass flow rate rises remains essentially unchanged,the total entropy production exhibits a nonmonotonic trend,first decreasing and then increasing with the mass flow rate.High entropy production in the impeller is primarily concentrated in the clearance region and along the rear cover of the impeller tip.In the diffuser,it is most pronounced on the front and rear plates and within the central flow path.Meanwhile,in the volute,the highest entropy production occurs around the diffuser outlet and along the outer region of the volute’s centerline.展开更多
Power consumption increases annually,wherefore the air emissions during its production occasionally increase.One of the most promising trends of environmentally safe generation of electricity is the transition to oxyg...Power consumption increases annually,wherefore the air emissions during its production occasionally increase.One of the most promising trends of environmentally safe generation of electricity is the transition to oxygen-fuel power complexes operating on a carbon dioxide working medium,with a share of its capture up to 99%.It is worth noting that the breadth of application of power technologies is determined not only on the basis of criteria of thermal efficiency and environmental safety.The most important criterion is the indicator of economic accessibility,the failure of which does not yet allow for a large-scale transition to the use of electric power technologies with the capture and disposal of greenhouse gases.In this study,a set of multifactorial models for estimating the cost of the main generating equipment operating on supercritical carbon dioxide has been developed.it is found that an increase in the initial temperature and pressure will increase the cost of the main generating equipment operating on supercritical carbon dioxide.展开更多
RP-3 is a kind of aviation kerosene commonly used in hypersonic and scramjet engines due to its superior thermal stability,high energy density,and ability to act as a coolant before combustion.However,it is known that...RP-3 is a kind of aviation kerosene commonly used in hypersonic and scramjet engines due to its superior thermal stability,high energy density,and ability to act as a coolant before combustion.However,it is known that coke can be generated during the cooling process as a carbonaceous deposition on metal walls and its effects on the cooling performance are still largely unknown.To explore the influence mechanism of porous coke on heat transfer characteristics of supercritical RP-3 in the regenerative cooling channel,a series of computational simulations were conducted via a three-dimensional CFD model considering solid wall,porous media and fluid simultaneously.The results show that the porous coke leads to the heat transfer deterioration,but when the coke layer thickness exceeds 1 mm,the weakening influence of coke on heat transfer becomes less important.The effect of porous coke on heat transfer under different inlet flow rates and wall heat fluxes was also analyzed and it was found that the heat exchange between channel wall and RP-3 is more detrimentally affected at large inlet mass flow rate.In a smooth channel,the heat transfer coefficient has a sudden rise along the flow direction,but the presence of porous coke mitigates the abrupt change.Furthermore,the variation of heat flux made a subtle difference in the effect of porous coke on the heat transfer of RP-3.展开更多
Flexible polymer-based foam sensors have significant potential for application in wearable electronics and motion monitoring.However,these prospects are hindered by the complex and unenvironmentally friendly manufactu...Flexible polymer-based foam sensors have significant potential for application in wearable electronics and motion monitoring.However,these prospects are hindered by the complex and unenvironmentally friendly manufacturing processes.In this study,we employed melt blending and supercritical carbon dioxide foaming to fabricate an ethylene-vinyl acetate copolymer(EVA)/low-density polyethylene(LDPE)/carbon nanotube(CNT)piezoresistive foam sensor.The cross-linking agent bis(tert-butyldioxyisopropyl)benzene and the conductive filler CNT were incorporated into the EVA/LDPE composite,successfully achieving a chemically cross-linked and physically entangled composite structure that significantly enhanced the storage modulus and complex viscosity.Additionally,the compressive strength of EVA/LDPE/CNT foam with 10 parts per hundred rubber(phr)CNT reached 1.37 MPa at 50%compression,marking a 340%increase compared to the 0.31 MPa of the CNT-free sample.Furthermore,the EVA/LDPE/CNT composite foams,which incorporated 10 phr CNT,were prepared under specific foaming conditions,resulting in an ultra-low density of 0.11 g/cm^(3) and a higher sensitivity,with a gauge factor of–2.3.The piezoresistive foam sensors developed in this work could accurately detect human motion,thereby expanding their applications in the field of piezoresistive foam sensors and providing an effective strategy for the advancement of high-performance piezoresistive foam sensors.展开更多
The study of the effects of supercritical CO_(2)(ScCO_(2))under high temperature and high pressure on the mechanical properties and fracturing potential of shale holds significant implications for advancing our unders...The study of the effects of supercritical CO_(2)(ScCO_(2))under high temperature and high pressure on the mechanical properties and fracturing potential of shale holds significant implications for advancing our understanding of enhanced shale gas extraction and reservoir exploration and development.This study examines the influence of three fluids,i.e.ScCO_(2),deionized water(DW),and ScCO_(2)tDW,on the mechanical properties and fracturability of shale at immersion pressures of 15 MPa and 45 MPa,with a constant temperature of 100C.The key findings are as follows:(1)Uniaxial compressive strength(UCS)of shale decreased by 10.72%,11.95%,and 23.67%at 15 MPa,and by 42.40%,46.84%,and 51.65%at 45 MPa after immersion in ScCO_(2),DW,and ScCO_(2)tDW,respectively,with the most pronounced effect observed in ScCO_(2)tDW;(2)Microstructural analysis revealed that while ScCO_(2)and DW do not significantly alter the microstructure,immersion in ScCO_(2)tDW results in a more complex surface morphology;(3)Acoustic emission(AE)analysis indicates a reduction in stress for crack damage,with a decreased fractal dimension of AE signals in different fluids.AE energy is primarily generated during the unstable crack propagation stage;(4)A quantitative method employing a multi-factor approach combined with the brittleness index(BI)effectively characterizes shale fracturability.Evaluation results show that ScCO_(2)tDW has a more significant effect on shale fracturability,with fracturability indices of 0.833%and 1.180%following soaking at 15 MPa and 45 MPa,respectively.Higher immersion pressure correlates positively with increased shale fracturability.展开更多
A much more sustainable,cost effective and very flexible process for manufacturing critical fibres based on ultra high molecular weight polyethylene(UHMWPE)is being launched by the UK’s Fibre Extrusion Technologies(F...A much more sustainable,cost effective and very flexible process for manufacturing critical fibres based on ultra high molecular weight polyethylene(UHMWPE)is being launched by the UK’s Fibre Extrusion Technologies(FET).展开更多
Although supercritical carbon dioxide(SC-CO_(2))fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes,few investigations have been reported on the SC-CO_(2) fracturing...Although supercritical carbon dioxide(SC-CO_(2))fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes,few investigations have been reported on the SC-CO_(2) fracturing characteristics of tight basalts and the reactions between fractured basalt and SC-CO_(2).In this study,hydraulic fracturing experiments were conducted on cylindrical basalt specimens using water and SC-CO_(2) as fracturing fluids.Geometric parameters were proposed to characterize the fracture morphologies based on the three-dimensional(3D)reconstructions of fracture networks.The rock slices with induced fractures after SC-CO_(2) fracturing were then processed for fluid(deionized water/SC-CO_(2))-basalt reaction tests.The experimental results demonstrate that SC-CO_(2) fracturing can induce complex and tortuous fractures with spatially dispersed morphologies.Other fracturing behaviors accompanying the acoustic emission(AE)signals and pump pressure changes show that the AE activity responds almost simultaneously to variation in the pump pressure.The fractured basalt blocks exposed to both SC-CO_(2) and water exhibit rough and uneven surfaces,along with decreased intensities in the element peaks,indicating that solubility trapping predominantly occurs during the early injection stage.The above findings provide a laboratory research basis for understanding the fracturing and sequestration issues related to effective CO_(2) utilization.展开更多
The corrosion behavior of 304LN austenitic stainless steel in supercritical CO_(2) at 650℃ was investigated.The results show that 304LN follows Wagner’s law kinetics,forming a protective oxide flm consisting of SiO_...The corrosion behavior of 304LN austenitic stainless steel in supercritical CO_(2) at 650℃ was investigated.The results show that 304LN follows Wagner’s law kinetics,forming a protective oxide flm consisting of SiO_(2),(Cr,Mn)3O_(4),and Cr2O_(3) from the inner to outer layers.A shallow carburization depth of approximately 130 nm indicates excellent resistance to carburization.The roles of key elements in 18/8 austenitic stainless steel represented by 304LN,such as Cr,Ni,and Si,were analyzed,highlighting their contributions to anti-carburization performance and corrosion resistance under harsh conditions.展开更多
Deep shale reservoirs are often associated with extreme geological conditions,including high tem-peratures,substantial horizontal stress differences,elevated closure stresses,and high breakdown pressures.These factors...Deep shale reservoirs are often associated with extreme geological conditions,including high tem-peratures,substantial horizontal stress differences,elevated closure stresses,and high breakdown pressures.These factors pose significant challenges to conventional hydraulic fracturing with water-based fluids,which may induce formation damage and fail to generate complex fracture networks.Supercritical carbon dioxide(SC-CO_(2)),with its low viscosity,high diffusivity,low surface tension,and minimal water sensitivity,has attracted growing attention as an alternative fracturing fluid for deep shale stimulation.This study presents a series of true triaxial large-scale physical experiments using shale samples from the Longmaxi Formation in the southern Sichuan Basin to investigate fracture initiation and propagation behavior under different fracturing fluids.The results show that,under identical experimental conditions,SC-CO_(2)fracturing results in a significantly lower breakdown pressure compared to slick water and promotes the formation of more complex fracture geometries.These advantages are attributed to both the favorable flow characteristics of SC-CO_(2)and its potential chemical interactions with shale minerals.The findings not only confirm the effectiveness of SC-CO_(2)as a fracturing fluid in deep shale environments but also provide new insights into its fracture propagation mechanisms.展开更多
High-water-cut mature reservoirs typically serve as the“ballast”for ensuring China’s annual crude oil production of 200 million tons.Despite the use of water flooding and chemical methods,over 40%of crude oil remai...High-water-cut mature reservoirs typically serve as the“ballast”for ensuring China’s annual crude oil production of 200 million tons.Despite the use of water flooding and chemical methods,over 40%of crude oil remains unexploited.It is critical to develop efficient revolutionary technologies to further enhance oil recovery(EOR)by a large percentage in high-water-cut mature reservoirs.To address this issue,the potential of vertical remaining oil in Daqing Oilfield is first analyzed from massive monitoring data.Using molecular dynamics simulation to design optimal synthetic routine,a copolymer without flu-orine or silicon is synthesized by modifying vinyl acetate(VAc)with maleic anhydride(MA)and styrene(St),and treated as a supercritical CO_(2)(scCO_(2))thickener.The underlying EOR mechanism of the scCO_(2) thickener is thereafter clarified by high-temperature,high-pressure oil displacement experiments.The EOR effect by thickened scCO_(2) flooding in a typical high-water-cut mature reservoir is predicted,and future technological advancements of the technique are ultimately discussed.Results show that the ver-tical remaining oil enriched in weakly swept zones is a primary target for further EOR in high-water-cut mature reservoirs.The copolymer typically exhibits good solubility,strong dispersion stability,and high thickening effect in scCO_(2).Under an ambient pressure of 10 MPa and a temperature of 50℃,the disso-lution of copolymer at a mass concentration of 0.2%can effectively increase the viscosity of scCO_(2) by 39.4 times.Due to the synergistic effect between expanding vertical swept volume and inhibiting gas channel-ing,crude oil recovery can be further enhanced by 23.1%for a typical high-water-cut mature reservoir when the scCO_(2) viscosity is increased by 50 times.Our understandings demonstrate that the thickened scCO_(2) flooding technology has significant technical advantages in high-water-cut mature reservoirs,with challenges and future development directions in field-scale applications also highlighted.展开更多
This paper investigates the macroscopic and microscopic characteristics of viscosity reduction and quality improvement of heavy oil in a supercritical water environment through laboratory experiments and testing.The e...This paper investigates the macroscopic and microscopic characteristics of viscosity reduction and quality improvement of heavy oil in a supercritical water environment through laboratory experiments and testing.The effect of three reaction parameters,i.e.reaction temperature,reaction time and oil-water ratio,is analyzed on the product and their correlation with viscosity.The results show that the flow state of heavy oil is significantly improved with a viscosity reduction of 99.4%in average after the reaction in the supercritical water.Excessively high reaction temperature leads to a higher content of resins and asphaltenes,with significantly increasing production of coke.The optimal temperature ranges in 380–420℃.Prolonged reaction time could continuously increase the yield of light oil,but it will also results in the growth of resins and asphaltenes,with the optimal reaction time of 150 min.Reducing the oil-water ratio helps improve the diffusion environment within the reaction system and reduce the content of resins and asphaltenes,but it will increase the cost of heavy oil treatment.An oil-water ratio of 1︰2 is considered as optimum to balance the quality improvement,viscosity reduction and reaction economics.The correlation of the three reaction parameters relative to the oil sample viscosity is ranked as temperature,time and oil-water ratio.Among the four fractions of heavy oil,the viscosity is dominated by asphaltene content,followed by aromatic content and less affected by resins and saturates contents.展开更多
The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure.This study is devoted to the an...The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure.This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region.By making use of the free energy,we introduce three key thermodynamic quantities:scaled variance,skewness,and kurtosis.Our results demonstrate that the Widom line,associated with the maximal scaled variance,can effectively differentiate between small and large black hole-like subphases,each displaying distinct thermodynamic behaviors within the supercritical region.Furthermore,by utilizing quasinormal modes,we identify the Frenkel line,offering a dynamic perspective to distinguish between small and large black hole-like subphases.These contribute to a deeper comprehension of black hole subphases in the supercritical region,thus illuminating new facets of black hole thermodynamics.展开更多
Alkaline water electrolysis poses significant potential for large-sc ale indus trial hydrogen generation,but is impeded by the absence of an efficient electrocatalyst capable of operating at high current densities whi...Alkaline water electrolysis poses significant potential for large-sc ale indus trial hydrogen generation,but is impeded by the absence of an efficient electrocatalyst capable of operating at high current densities while maintaining with minimal overpotential.Herein,we construct a mechanically stable and highly active RuSe_(2)/MXene heterojunction electrocatalyst.A typical SC-Ti_(3)C_(2)T_(x)MXene substrate was successfully prepared by supercritical CO_(2)(SC-CO_(2))etching,combined by subsequent DMSO intercalation treatment.Further,the RuSe_(2)nanoparticles were uniformly deposited on the surface of SC-Ti_(3)C_(2)T_(x).Theoretical calculations and experimental results demonstrate that fluorine-rich MXene exhibits stable binding with the active 1T phase RuSe_(2).The as-prepared representative RuSe_(2)@SC-Ti_(3)C_(2)T_(x)-3 heterostructure showed exceptional alkaline hydrogen evolution performance,demonstrating an overpotential of 15 mV at 10 mA cm^(-2)and a Tafel slope of 21.84 mV dec^(-1),which presents excellent HER performance and stability at high-current-density conditions.Moreover,the overpotential under the current density of 500 mA cm^(-2)is merely 182 mV,and the HER efficiency remains unaffected even after 5000 cycles and 120 h of continuous testing.展开更多
Allelochemicals of Chinese-fir root was extracted by technology of supercritical CO2 extraction under orthogonal experiment design, and it was used to analyze allelopathic activity of Chinese-fir through bioassay of s...Allelochemicals of Chinese-fir root was extracted by technology of supercritical CO2 extraction under orthogonal experiment design, and it was used to analyze allelopathic activity of Chinese-fir through bioassay of seed germination. The results showed that as to the available rate of allelochemicals, the pressure and temperature of extraction were the most important factors. The allelochemicals of Chinese-fir root extracted by pure CO2 and ethanol mixed with CO2 have different allelopathic activities to seed germination, and the allelochemicals extracted by ethanol mixed with CO2 had stronger inhibitory effects on seed germination than that extracted by pure CO2.展开更多
基金funded by the National Natural Scientific Foundation of China(Nos.52304008,52404038,52474043)the China Postdoctoral Science Foundation(No.2023MD734223)+1 种基金the Key Laboratory of Well Stability and Fluid&Rock Mechanics in Oil and Gas Reservoir of Shaanxi Province(No.23JS047)the Youth Talent Lifting Program of Xi'an Science and Technology Association(No.959202413078)。
文摘Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.
文摘With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,shale oil and gas reservoirs have become the focus of unconventional oil and gas resources exploration and development.Based on the characteristics of shale oil and gas reservoirs,supercritical CO_(2) fracturing is more conducive to improving oil recovery than other fracturing technologies.In this paper,the mechanism of fracture initiation and propagation of supercritical CO_(2) in shale is analyzed,including viscosity effect,surface tension effect,permeation diffusion effect of supercritical CO_(2),and dissolution-adsorption effect between CO_(2) and shale.The effects of natural factors,such as shale properties,bedding plane and natural fractures,and controllable factors,proppant,temperature,pressure,CO_(2) concentration and injection rate on fracture initiation and propagation are clarified.The methods of supercritical CO_(2) fracturing process,thickener and proppant optimization to improve the efficiency of supercritical CO_(2) fracturing are discussed.In addition,some new technologies of supercritical CO_(2) fracturing are introduced.The challenges and prospects in the current research are also summarized.For example,supercritical CO_(2) is prone to filtration when passing through porous media,and it is difficult to form a stable flow state.Therefore,in order to achieve stable fracturing fluid suspension and effectively support fractu res,it is urge nt to explo re new fracturing fluid additives or improve fracturing fluid formulations combined with the research of new proppants.This paper is of great significance for understanding the behavior mechanism of supercritical CO_(2) in shale and optimizing fracturing technology.
基金supported by the Fundamental Research Funds for the Central Universities(2024KYJD2006).
文摘We consider the multiplicity of solutions to a p(x)-Laplacian problem involving supercritical Sobolev growth via Ricceri’s principle.By means of truncation combined with De Giorgi iteration,we can extend the results of subcritical and critical growth to supercritical growth and obtain at least three solutions to the p(x)-Laplacian problem.
基金support by the Basic Science Center Program of the Ordered Energy Conversion of the National Nature Science Foundation of China(NO.52488201)is gratefully acknowledged.
文摘Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products.In this paper,the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale.The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared.The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified.The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction,and gradually increased with increasing time.The prediction error can reach less than 25%when the reaction time was 12 h.The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas,and its prediction error is less than 14%in this paper.The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon,asphaltene pyrolysis generates saturated hydrocarbon,aromatic hydrocarbon and resin,saturated hydrocarbon,aromatic hydrocarbon and resin polymerization generates asphaltene,and saturated hydrocarbon,resin and asphaltene generates gas.The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFE0117200)the National Natural Science Foundation of China(Grant No.41977304).
文摘Understanding the solubility of supercritical CO_(2)and its mixtures with other fluids at various temperatures and pressures conditions is critical for their applications,such as extraction processes,material design,and carbon capture.In the present study,the solubility parameters of supercritical CO_(2),H_(2)O,and their mixtures were calculated by molecular dynamics simulations.The results show that the solubility parameters decrease with increasing temperature and increase with increasing pressure and are linearly proportional to the density.Furthermore,the intermolecular interactions,including the hydrogen bonds,significantly affect the solubility parameter of the CO_(2)-H_(2)O system.
基金supported by the Science Center for Gas Turbine Project,China(No.P2022-C-II-005-001)。
文摘Aviation kerosene RP-3 is extensively used in China.This paper details the measurement of the density of Chinese aviation kerosene RP-3 employing the flow method under high-pressure and high-temperature conditions.The methodology utilizes circular tubes with two different diameters.The density of aviation kerosene RP-3 was experimentally measured for the first time within a pressure range from 6 MPa to 8 MPa and a temperature range from 323 K to 783 K,with a maximum relative uncertainty of 0.35%.The experimental setup used n-decane for calibration,achieving an average calibration error of 0.91%.The data indicate that the density of RP-3 ranges from 764 kg/m^(3)to 247 kg/m^(3)under the tested conditions.The results show that the density of kerosene RP-3 decreases with an increase in temperature at a constant pressure,and at a given temperature,a higher pressure results in a higher density.Polynomial fitting was applied to the data,resulting in the average absolute deviation of 1.09%,0.80%,and 0.76%at different pressures of 6,7,and 8 MPa,respectively.
基金supported by theDouble First-Class Key ProgramofGansu ProvincialDepartment of Education(grant number GCJ2022-38)Science and Technology Program of Gansu Province(grant number 22ZD6GA038)Key Research and Development Program of Gansu Province—Industrial Project(grant number 25YFGA021).
文摘In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential for enhancing the performance of such systems.This study examines the main sCO_(2) compressor from Sandia Laboratory,utilizing entropy production theory to elucidate the sources and distribution of energy losses both across the entire machine and within its key flow components.The findings reveal that turbulent viscous dissipation is the predominant contributor to total entropy production.Interestingly,while the relative importance of the entropy produced by various sources as the mass flow rate rises remains essentially unchanged,the total entropy production exhibits a nonmonotonic trend,first decreasing and then increasing with the mass flow rate.High entropy production in the impeller is primarily concentrated in the clearance region and along the rear cover of the impeller tip.In the diffuser,it is most pronounced on the front and rear plates and within the central flow path.Meanwhile,in the volute,the highest entropy production occurs around the diffuser outlet and along the outer region of the volute’s centerline.
基金This study conducted by Moscow Power Engineering Institute was financially supported by the Ministry of Science and Higher Education of the Russian Federation(project No.FSWF-2023-0014,contract No.075-03-2023-383,2023/18/01).
文摘Power consumption increases annually,wherefore the air emissions during its production occasionally increase.One of the most promising trends of environmentally safe generation of electricity is the transition to oxygen-fuel power complexes operating on a carbon dioxide working medium,with a share of its capture up to 99%.It is worth noting that the breadth of application of power technologies is determined not only on the basis of criteria of thermal efficiency and environmental safety.The most important criterion is the indicator of economic accessibility,the failure of which does not yet allow for a large-scale transition to the use of electric power technologies with the capture and disposal of greenhouse gases.In this study,a set of multifactorial models for estimating the cost of the main generating equipment operating on supercritical carbon dioxide has been developed.it is found that an increase in the initial temperature and pressure will increase the cost of the main generating equipment operating on supercritical carbon dioxide.
基金funded by Natural Science Foundation of Chongqing(No.CSTB2022NSCQ-MSX0416)Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)(No.PLN2020-8)+2 种基金Open Fund of Chongqing Key Laboratory of Fire and Explosion Safe(No.LQ21KFJJ02)Open Fund of State Key Laboratory of High Temperature Gas Dynamics(No.2021KF14)Sichuan Science and Technology Program(No.2022YFH0017)。
文摘RP-3 is a kind of aviation kerosene commonly used in hypersonic and scramjet engines due to its superior thermal stability,high energy density,and ability to act as a coolant before combustion.However,it is known that coke can be generated during the cooling process as a carbonaceous deposition on metal walls and its effects on the cooling performance are still largely unknown.To explore the influence mechanism of porous coke on heat transfer characteristics of supercritical RP-3 in the regenerative cooling channel,a series of computational simulations were conducted via a three-dimensional CFD model considering solid wall,porous media and fluid simultaneously.The results show that the porous coke leads to the heat transfer deterioration,but when the coke layer thickness exceeds 1 mm,the weakening influence of coke on heat transfer becomes less important.The effect of porous coke on heat transfer under different inlet flow rates and wall heat fluxes was also analyzed and it was found that the heat exchange between channel wall and RP-3 is more detrimentally affected at large inlet mass flow rate.In a smooth channel,the heat transfer coefficient has a sudden rise along the flow direction,but the presence of porous coke mitigates the abrupt change.Furthermore,the variation of heat flux made a subtle difference in the effect of porous coke on the heat transfer of RP-3.
基金supported by the National Natural Science Foundation of China(No.52473026)。
文摘Flexible polymer-based foam sensors have significant potential for application in wearable electronics and motion monitoring.However,these prospects are hindered by the complex and unenvironmentally friendly manufacturing processes.In this study,we employed melt blending and supercritical carbon dioxide foaming to fabricate an ethylene-vinyl acetate copolymer(EVA)/low-density polyethylene(LDPE)/carbon nanotube(CNT)piezoresistive foam sensor.The cross-linking agent bis(tert-butyldioxyisopropyl)benzene and the conductive filler CNT were incorporated into the EVA/LDPE composite,successfully achieving a chemically cross-linked and physically entangled composite structure that significantly enhanced the storage modulus and complex viscosity.Additionally,the compressive strength of EVA/LDPE/CNT foam with 10 parts per hundred rubber(phr)CNT reached 1.37 MPa at 50%compression,marking a 340%increase compared to the 0.31 MPa of the CNT-free sample.Furthermore,the EVA/LDPE/CNT composite foams,which incorporated 10 phr CNT,were prepared under specific foaming conditions,resulting in an ultra-low density of 0.11 g/cm^(3) and a higher sensitivity,with a gauge factor of–2.3.The piezoresistive foam sensors developed in this work could accurately detect human motion,thereby expanding their applications in the field of piezoresistive foam sensors and providing an effective strategy for the advancement of high-performance piezoresistive foam sensors.
基金financial support from the Science and Technology Innovation Program of Hunan Province(Grant No.2023RC1021)the National Natural Science Foundation of China(Grant No.52231012)+1 种基金the Natural Science Foundation of Hainan Province(Grant No.424QN213)the Scientific Research Foundation of Hainan University.
文摘The study of the effects of supercritical CO_(2)(ScCO_(2))under high temperature and high pressure on the mechanical properties and fracturing potential of shale holds significant implications for advancing our understanding of enhanced shale gas extraction and reservoir exploration and development.This study examines the influence of three fluids,i.e.ScCO_(2),deionized water(DW),and ScCO_(2)tDW,on the mechanical properties and fracturability of shale at immersion pressures of 15 MPa and 45 MPa,with a constant temperature of 100C.The key findings are as follows:(1)Uniaxial compressive strength(UCS)of shale decreased by 10.72%,11.95%,and 23.67%at 15 MPa,and by 42.40%,46.84%,and 51.65%at 45 MPa after immersion in ScCO_(2),DW,and ScCO_(2)tDW,respectively,with the most pronounced effect observed in ScCO_(2)tDW;(2)Microstructural analysis revealed that while ScCO_(2)and DW do not significantly alter the microstructure,immersion in ScCO_(2)tDW results in a more complex surface morphology;(3)Acoustic emission(AE)analysis indicates a reduction in stress for crack damage,with a decreased fractal dimension of AE signals in different fluids.AE energy is primarily generated during the unstable crack propagation stage;(4)A quantitative method employing a multi-factor approach combined with the brittleness index(BI)effectively characterizes shale fracturability.Evaluation results show that ScCO_(2)tDW has a more significant effect on shale fracturability,with fracturability indices of 0.833%and 1.180%following soaking at 15 MPa and 45 MPa,respectively.Higher immersion pressure correlates positively with increased shale fracturability.
文摘A much more sustainable,cost effective and very flexible process for manufacturing critical fibres based on ultra high molecular weight polyethylene(UHMWPE)is being launched by the UK’s Fibre Extrusion Technologies(FET).
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant No.42320104003)the Shanghai Pujiang Programme(Grant No.23PJD105).
文摘Although supercritical carbon dioxide(SC-CO_(2))fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes,few investigations have been reported on the SC-CO_(2) fracturing characteristics of tight basalts and the reactions between fractured basalt and SC-CO_(2).In this study,hydraulic fracturing experiments were conducted on cylindrical basalt specimens using water and SC-CO_(2) as fracturing fluids.Geometric parameters were proposed to characterize the fracture morphologies based on the three-dimensional(3D)reconstructions of fracture networks.The rock slices with induced fractures after SC-CO_(2) fracturing were then processed for fluid(deionized water/SC-CO_(2))-basalt reaction tests.The experimental results demonstrate that SC-CO_(2) fracturing can induce complex and tortuous fractures with spatially dispersed morphologies.Other fracturing behaviors accompanying the acoustic emission(AE)signals and pump pressure changes show that the AE activity responds almost simultaneously to variation in the pump pressure.The fractured basalt blocks exposed to both SC-CO_(2) and water exhibit rough and uneven surfaces,along with decreased intensities in the element peaks,indicating that solubility trapping predominantly occurs during the early injection stage.The above findings provide a laboratory research basis for understanding the fracturing and sequestration issues related to effective CO_(2) utilization.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA0410000)the CAS Project for Young Scientists in Basic Research(No.YSBR-043)+1 种基金the CNNC Science Fund for Talented Young Scholars,the National Funding Program for Postdoctoral Researchers(GZC20232747)the Youth Innovation Promotion Association CAS(2022187).
文摘The corrosion behavior of 304LN austenitic stainless steel in supercritical CO_(2) at 650℃ was investigated.The results show that 304LN follows Wagner’s law kinetics,forming a protective oxide flm consisting of SiO_(2),(Cr,Mn)3O_(4),and Cr2O_(3) from the inner to outer layers.A shallow carburization depth of approximately 130 nm indicates excellent resistance to carburization.The roles of key elements in 18/8 austenitic stainless steel represented by 304LN,such as Cr,Ni,and Si,were analyzed,highlighting their contributions to anti-carburization performance and corrosion resistance under harsh conditions.
文摘Deep shale reservoirs are often associated with extreme geological conditions,including high tem-peratures,substantial horizontal stress differences,elevated closure stresses,and high breakdown pressures.These factors pose significant challenges to conventional hydraulic fracturing with water-based fluids,which may induce formation damage and fail to generate complex fracture networks.Supercritical carbon dioxide(SC-CO_(2)),with its low viscosity,high diffusivity,low surface tension,and minimal water sensitivity,has attracted growing attention as an alternative fracturing fluid for deep shale stimulation.This study presents a series of true triaxial large-scale physical experiments using shale samples from the Longmaxi Formation in the southern Sichuan Basin to investigate fracture initiation and propagation behavior under different fracturing fluids.The results show that,under identical experimental conditions,SC-CO_(2)fracturing results in a significantly lower breakdown pressure compared to slick water and promotes the formation of more complex fracture geometries.These advantages are attributed to both the favorable flow characteristics of SC-CO_(2)and its potential chemical interactions with shale minerals.The findings not only confirm the effectiveness of SC-CO_(2)as a fracturing fluid in deep shale environments but also provide new insights into its fracture propagation mechanisms.
基金the National Natural Science Foundation of China(U22B6005,52174043,52474035)the Beijing Natural Science Foundation(3242019)the China National Petroleum Corporation(CNPC)Innovation Foundation(2022DQ02-0208 and 2024DQ02-0114).
文摘High-water-cut mature reservoirs typically serve as the“ballast”for ensuring China’s annual crude oil production of 200 million tons.Despite the use of water flooding and chemical methods,over 40%of crude oil remains unexploited.It is critical to develop efficient revolutionary technologies to further enhance oil recovery(EOR)by a large percentage in high-water-cut mature reservoirs.To address this issue,the potential of vertical remaining oil in Daqing Oilfield is first analyzed from massive monitoring data.Using molecular dynamics simulation to design optimal synthetic routine,a copolymer without flu-orine or silicon is synthesized by modifying vinyl acetate(VAc)with maleic anhydride(MA)and styrene(St),and treated as a supercritical CO_(2)(scCO_(2))thickener.The underlying EOR mechanism of the scCO_(2) thickener is thereafter clarified by high-temperature,high-pressure oil displacement experiments.The EOR effect by thickened scCO_(2) flooding in a typical high-water-cut mature reservoir is predicted,and future technological advancements of the technique are ultimately discussed.Results show that the ver-tical remaining oil enriched in weakly swept zones is a primary target for further EOR in high-water-cut mature reservoirs.The copolymer typically exhibits good solubility,strong dispersion stability,and high thickening effect in scCO_(2).Under an ambient pressure of 10 MPa and a temperature of 50℃,the disso-lution of copolymer at a mass concentration of 0.2%can effectively increase the viscosity of scCO_(2) by 39.4 times.Due to the synergistic effect between expanding vertical swept volume and inhibiting gas channel-ing,crude oil recovery can be further enhanced by 23.1%for a typical high-water-cut mature reservoir when the scCO_(2) viscosity is increased by 50 times.Our understandings demonstrate that the thickened scCO_(2) flooding technology has significant technical advantages in high-water-cut mature reservoirs,with challenges and future development directions in field-scale applications also highlighted.
基金Supported by the Foundation for Innovative Research Groups of National Natural Science Foundation of China(52421002)General Program of National Natural Science Foundation of China(52474016).
文摘This paper investigates the macroscopic and microscopic characteristics of viscosity reduction and quality improvement of heavy oil in a supercritical water environment through laboratory experiments and testing.The effect of three reaction parameters,i.e.reaction temperature,reaction time and oil-water ratio,is analyzed on the product and their correlation with viscosity.The results show that the flow state of heavy oil is significantly improved with a viscosity reduction of 99.4%in average after the reaction in the supercritical water.Excessively high reaction temperature leads to a higher content of resins and asphaltenes,with significantly increasing production of coke.The optimal temperature ranges in 380–420℃.Prolonged reaction time could continuously increase the yield of light oil,but it will also results in the growth of resins and asphaltenes,with the optimal reaction time of 150 min.Reducing the oil-water ratio helps improve the diffusion environment within the reaction system and reduce the content of resins and asphaltenes,but it will increase the cost of heavy oil treatment.An oil-water ratio of 1︰2 is considered as optimum to balance the quality improvement,viscosity reduction and reaction economics.The correlation of the three reaction parameters relative to the oil sample viscosity is ranked as temperature,time and oil-water ratio.Among the four fractions of heavy oil,the viscosity is dominated by asphaltene content,followed by aromatic content and less affected by resins and saturates contents.
基金supported by the National Natural Science Foundation of China(Grant Nos.12473001,11975072,11875102,11835009,and 11965013)the National SKA Program of China(Grant Nos.2022SKA0110200 and 2022SKA0110203)+1 种基金the National 111 Project(Grant No.B16009)supported by Yunnan High-level Talent Training Support Plan Young&Elite Talents Project(Grant No.YNWR-QNBJ-2018-181).
文摘The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure.This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region.By making use of the free energy,we introduce three key thermodynamic quantities:scaled variance,skewness,and kurtosis.Our results demonstrate that the Widom line,associated with the maximal scaled variance,can effectively differentiate between small and large black hole-like subphases,each displaying distinct thermodynamic behaviors within the supercritical region.Furthermore,by utilizing quasinormal modes,we identify the Frenkel line,offering a dynamic perspective to distinguish between small and large black hole-like subphases.These contribute to a deeper comprehension of black hole subphases in the supercritical region,thus illuminating new facets of black hole thermodynamics.
基金financially supported by the China Postdoctoral Science Foundation(Nos.2021TQ0300 and 2021M702946)Henan Science and Technology Department(Nos.242102231034 and 242301420040)+1 种基金the joint project from Henan Province,the China-National Natural Science Foundation(No.U2004208)the Central Plains Science and Technology Innovation Leading Talent Project(No.234200510008)
文摘Alkaline water electrolysis poses significant potential for large-sc ale indus trial hydrogen generation,but is impeded by the absence of an efficient electrocatalyst capable of operating at high current densities while maintaining with minimal overpotential.Herein,we construct a mechanically stable and highly active RuSe_(2)/MXene heterojunction electrocatalyst.A typical SC-Ti_(3)C_(2)T_(x)MXene substrate was successfully prepared by supercritical CO_(2)(SC-CO_(2))etching,combined by subsequent DMSO intercalation treatment.Further,the RuSe_(2)nanoparticles were uniformly deposited on the surface of SC-Ti_(3)C_(2)T_(x).Theoretical calculations and experimental results demonstrate that fluorine-rich MXene exhibits stable binding with the active 1T phase RuSe_(2).The as-prepared representative RuSe_(2)@SC-Ti_(3)C_(2)T_(x)-3 heterostructure showed exceptional alkaline hydrogen evolution performance,demonstrating an overpotential of 15 mV at 10 mA cm^(-2)and a Tafel slope of 21.84 mV dec^(-1),which presents excellent HER performance and stability at high-current-density conditions.Moreover,the overpotential under the current density of 500 mA cm^(-2)is merely 182 mV,and the HER efficiency remains unaffected even after 5000 cycles and 120 h of continuous testing.
基金This paper was supported by Natural Science Foundation of Fujian Province (B0010020)
文摘Allelochemicals of Chinese-fir root was extracted by technology of supercritical CO2 extraction under orthogonal experiment design, and it was used to analyze allelopathic activity of Chinese-fir through bioassay of seed germination. The results showed that as to the available rate of allelochemicals, the pressure and temperature of extraction were the most important factors. The allelochemicals of Chinese-fir root extracted by pure CO2 and ethanol mixed with CO2 have different allelopathic activities to seed germination, and the allelochemicals extracted by ethanol mixed with CO2 had stronger inhibitory effects on seed germination than that extracted by pure CO2.
