The thermal flux curve of phase-transition fluid(PF)was tested using differential scanning calorimetry,based on which a reaction kinetics model was established to reflect the relationship between phase transition conv...The thermal flux curve of phase-transition fluid(PF)was tested using differential scanning calorimetry,based on which a reaction kinetics model was established to reflect the relationship between phase transition conversion rate,temperature and time.A temperature field model for fractures and rock matrix considering phase transition heat was then constructed,and its reliability was verified using previously established temperature field models.Additionally,the new model was used to study the effects of different injection parameters and phase-transition fracturing performance parameters on the temperature variations in fractures and matrix.The study indicates that,at different positions and times,the cooling effect of the injected cold fluid and the exothermic effect during the phase transition alternately dominate the temperature within the fracture.At the initial stage of fracturing fluid injection,the temperature within the fracture is high,and the phase transition rate is rapid,resulting in a significant impact of exothermic phase transition on the reservoir rock temperature.In the later stage of injection,the fracture temperature decreases,the phase transition exothermic rate slows,and the cooling effect of the fracturing fluid on the reservoir rock intensifies.Phase transition heat significantly affects the temperature of the fracture.Compared to cases where phase transition heat is not considered,when it is taken into account,the temperature within the fracture increases to varying degrees at the end of fluid injection.As the phase transition heat increases from 20 J/g to 60 J/g,the maximum temperature rise in the fracture increases from 2.1℃ to 6.2℃.The phase transition heat and PF volume fraction are positively correlated with fracture temperature changes,while specific heat capacity is negatively correlated with temperature changes.With increasing injection time,the temperature and phase transition rate at the fracture opening gradually decrease,and the location of the maximum phase transition rate and temperature difference gradually shifts from the fracture opening to about 10 m from the opening.展开更多
In this paper, we investigate the self-propelled particles confined on a spherical substrate and explore the structural and dynamic properties of self-propelled particles by controlling the packing fraction and activi...In this paper, we investigate the self-propelled particles confined on a spherical substrate and explore the structural and dynamic properties of self-propelled particles by controlling the packing fraction and activity. We find that these self-propelled particles freeze into the crystal with the increase in the packing fraction. We observe the pattern evolution of inevitable topological defects due to the geometric constraints of the spherical substrate. During the process of freezing, there is a transition from twelve isolated grain boundaries to the uniform distribution of defects with the increase in the self-propelled velocity. Finally, we establish a phase diagram of the freezing process. These results may deepen our understanding of active particles in complex and crowded environments.展开更多
Shale gas is an important unconventional resource.The economic recovery of shale gas is only possible when a fracture network with sufficient conductivity is created by hydraulic fracturing,that,if effectively propped...Shale gas is an important unconventional resource.The economic recovery of shale gas is only possible when a fracture network with sufficient conductivity is created by hydraulic fracturing,that,if effectively propped,connects fracturing fractures and natural fractures.Focusing on the Longmaxi shale in the Sichuan Basin,Southwest China,we built an optimization model for conductivity of multi-grade fractures based on equivalent seepage theory.We then experimentally analyzed the conductivity of self-propped and sand-propped fractures,and optimized the propping patterns of multi-grade hydraulic fractures in shale gas reservoirs.We concluded that the propping effectiveness of fracture networks could be improved by using low concentrations of small-sized sands and by focusing on creating a large number of self-propped fractures.By applying this understanding to the optimization of fracturing designs for the Longmaxi shale,we successfully created networks of well-propped fractures.展开更多
In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.I...In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.In this paper,the mineral composition characteristics,reservoir pore and fracture characteristics of shale were investigated,and the permeability of three types of induced fractures in shale(i.e.,in-situ closed type,shear self-propped type and single-layer propped type)was tested.Besides,the effects of fracture type,fracture surface roughness,carbonate content,shale bedding and confining pressure on the permeability of induced fractures in shale reservoirs were studied systematically.The following research results were obtained.First,the permeabilityepressure relationship of in-situ closed fracture is in accordance with the Walsh theory.The permeability decreases with the increase of confining pressure and it is in the range of 0.13e16.75 mD.In-situ closed fracture plays the same role in increasing the productivity of shale gas reservoirs with or without proppant filling or dislocation.Second,compared with in-situ closed fracture permeability,the shear self-propped fracture permeability is 1e2 orders of magnitude(7.53e88.48 mD)higher,and single-layer propped fracture permeability is 2e3 orders of magnitude(9.98e771.82 mD)higher.Third,the larger the fracture surface roughness,the higher the fracture permeability.And there is a better positive correlation between the fractal dimension and the fracture permeability.Fourth,the permeabilityepressure relationship of shear self-propped fracture and single-layer propped fracture is,to some extent,deviated from the Walsh theory,which reflects the influence of self-propped point crushing,proppant embedding and crushing.In conclusion,the experimental results can be used as the reference for the selection of shale fracturing technologies and the optimization of parameters.展开更多
基金Supported by the China Postdoctoral Science Foundation(2024M752803)the Open Fund of Key Laboratory of Deep Geothermal Resources of Ministry of Natural Resources(KLDGR2024B01)+1 种基金the National Natural Science Foundation of China(52179112)the Open Fund of National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)(PLN2023-02)。
文摘The thermal flux curve of phase-transition fluid(PF)was tested using differential scanning calorimetry,based on which a reaction kinetics model was established to reflect the relationship between phase transition conversion rate,temperature and time.A temperature field model for fractures and rock matrix considering phase transition heat was then constructed,and its reliability was verified using previously established temperature field models.Additionally,the new model was used to study the effects of different injection parameters and phase-transition fracturing performance parameters on the temperature variations in fractures and matrix.The study indicates that,at different positions and times,the cooling effect of the injected cold fluid and the exothermic effect during the phase transition alternately dominate the temperature within the fracture.At the initial stage of fracturing fluid injection,the temperature within the fracture is high,and the phase transition rate is rapid,resulting in a significant impact of exothermic phase transition on the reservoir rock temperature.In the later stage of injection,the fracture temperature decreases,the phase transition exothermic rate slows,and the cooling effect of the fracturing fluid on the reservoir rock intensifies.Phase transition heat significantly affects the temperature of the fracture.Compared to cases where phase transition heat is not considered,when it is taken into account,the temperature within the fracture increases to varying degrees at the end of fluid injection.As the phase transition heat increases from 20 J/g to 60 J/g,the maximum temperature rise in the fracture increases from 2.1℃ to 6.2℃.The phase transition heat and PF volume fraction are positively correlated with fracture temperature changes,while specific heat capacity is negatively correlated with temperature changes.With increasing injection time,the temperature and phase transition rate at the fracture opening gradually decrease,and the location of the maximum phase transition rate and temperature difference gradually shifts from the fracture opening to about 10 m from the opening.
基金Project supported by the National Natural Science Foundation of China(Nos.11622222,11472271,and 11872357)the Thousand Young Talents Program of China+1 种基金the Fundamental Research Fund for the Central Universitiesthe Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB22040403)
文摘In this paper, we investigate the self-propelled particles confined on a spherical substrate and explore the structural and dynamic properties of self-propelled particles by controlling the packing fraction and activity. We find that these self-propelled particles freeze into the crystal with the increase in the packing fraction. We observe the pattern evolution of inevitable topological defects due to the geometric constraints of the spherical substrate. During the process of freezing, there is a transition from twelve isolated grain boundaries to the uniform distribution of defects with the increase in the self-propelled velocity. Finally, we establish a phase diagram of the freezing process. These results may deepen our understanding of active particles in complex and crowded environments.
基金This study was supported by the National Major Science and Technology Project(No.2016ZX05060-004 and 2016ZX05023-001)the Petro China Major Science and Technology Project(No.2016E-0612).
文摘Shale gas is an important unconventional resource.The economic recovery of shale gas is only possible when a fracture network with sufficient conductivity is created by hydraulic fracturing,that,if effectively propped,connects fracturing fractures and natural fractures.Focusing on the Longmaxi shale in the Sichuan Basin,Southwest China,we built an optimization model for conductivity of multi-grade fractures based on equivalent seepage theory.We then experimentally analyzed the conductivity of self-propped and sand-propped fractures,and optimized the propping patterns of multi-grade hydraulic fractures in shale gas reservoirs.We concluded that the propping effectiveness of fracture networks could be improved by using low concentrations of small-sized sands and by focusing on creating a large number of self-propped fractures.By applying this understanding to the optimization of fracturing designs for the Longmaxi shale,we successfully created networks of well-propped fractures.
基金supported by National Major Science and Technology Project“Horizontal well fracturing design optimization system”(No.2016ZX05023-001).
文摘In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.In this paper,the mineral composition characteristics,reservoir pore and fracture characteristics of shale were investigated,and the permeability of three types of induced fractures in shale(i.e.,in-situ closed type,shear self-propped type and single-layer propped type)was tested.Besides,the effects of fracture type,fracture surface roughness,carbonate content,shale bedding and confining pressure on the permeability of induced fractures in shale reservoirs were studied systematically.The following research results were obtained.First,the permeabilityepressure relationship of in-situ closed fracture is in accordance with the Walsh theory.The permeability decreases with the increase of confining pressure and it is in the range of 0.13e16.75 mD.In-situ closed fracture plays the same role in increasing the productivity of shale gas reservoirs with or without proppant filling or dislocation.Second,compared with in-situ closed fracture permeability,the shear self-propped fracture permeability is 1e2 orders of magnitude(7.53e88.48 mD)higher,and single-layer propped fracture permeability is 2e3 orders of magnitude(9.98e771.82 mD)higher.Third,the larger the fracture surface roughness,the higher the fracture permeability.And there is a better positive correlation between the fractal dimension and the fracture permeability.Fourth,the permeabilityepressure relationship of shear self-propped fracture and single-layer propped fracture is,to some extent,deviated from the Walsh theory,which reflects the influence of self-propped point crushing,proppant embedding and crushing.In conclusion,the experimental results can be used as the reference for the selection of shale fracturing technologies and the optimization of parameters.
