Proppant flowback in the post-fracturing flowback period not only reduces the fracture conductivity but also damages equipment.Due to the current lack of experimental or numerical simulation methods for proppant flowb...Proppant flowback in the post-fracturing flowback period not only reduces the fracture conductivity but also damages equipment.Due to the current lack of experimental or numerical simulation methods for proppant flowback in partial closure fracture,the mechanisms and patterns of proppant flowback remain unclear.This makes it difficult to predict the risks of proppant flowback,leaving flowback program design without theoretical guidance and resulting in high uncertainty in prevention effectiveness.This paper has further modified the CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)coupling interface by introducing fracture closure pressure into the particle motion equation.Based on the dynamic mesh,the fracture width in the CFD model is adjusted in real time to establish a numerical simulation method that considers fracture closure and synchronous changes in the flow field.By establishing flow similarity at the perforations,a near-wellbore flow field is created in the scaled model that is representative of field conditions,ensuring the practical value of the experimental results.Based on proppant particle force analysis during flowback,we investigated the impact of closure pressure,friction coefficient,perforation parameters,fracture dip angle,proppant particle size combination on proppant flowback.The research indicates that the existence of a threshold closure pressure arises from the competition between the lateral force(driving flowback)exerted by fracture closure on particles and the frictional force(resisting flowback)acting on particles.Below this threshold,increasing closure pressure enhances near-wellbore proppant flowback;above this threshold,increased closure pressure reduces proppant flowback.This threshold value is determined to be 1 MPa under the simulation conditions of this paper.The friction coefficient between particles and the fracture wall has greater impact on particle flowback than the friction coefficient between particles.In the vertical direction of the fracture,flowback is more probable for particles above the perforation.There is higher risk of particle flowback in horizontal fractures.The lateral distribution of large and small particles is more effective in preventing flowback than the vertical distribution.In the horizontal direction,particles nearer to the perforation have a higher probability of flowback.Strategies for proppant flowback control:the flow rate should be kept low initially,and then increased after the bottomhole pressure has been appropriately reduced;perforations should be placed in the upper part of the reservoir(vertical well);the sand concentration should not be increased in the later stages of fracturing to reduce the accumulation of proppant above the perforations;different size proppants should be injected in smaller sizes followed by larger sizes,with a slug of clean fluid in between to achieve a side-by-side placement of larger and smaller proppant,thereby mitigating proppant flowback.展开更多
Near-infrared Ⅱ(NIR-Ⅱ)fluorescent nanoparticles(NPs)based on aggregation-induced emission(AIE)have attracted significant attention due to theirmultimodal imaging capabilities aswell as the combined photothermal and ...Near-infrared Ⅱ(NIR-Ⅱ)fluorescent nanoparticles(NPs)based on aggregation-induced emission(AIE)have attracted significant attention due to theirmultimodal imaging capabilities aswell as the combined photothermal and photodynamic therapeutic effects in cancer therapy.Reported herein is the rational designed AIE molecule(BPT),via incorporating phenothiazine units with strong electron-donating and reactive oxygen species(ROS)generation capabilities into the classical AIE scaffold tetraphenylethylene,further coupled with a strong electron-acceptor named benzo[1,2-c:4,5-c’]bis[1,2,5]thiadiazole.The BPT NPs exhibited maximum NIR-Ⅱ fluorescence emission at 1083 nm,a fluorescence quantum yield of 1.53%,photothermal conversion efficiency of 63%,and photoacoustic imaging capabilities,alongside considerable type I ROS generation ability.Additionally,when a kind of nitric oxide(NO)donor named O_(2)-(2,4-dinitrophenyl)1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate(JSK)was incorporated,the corresponding JSK-BPT NPs could generate O_(2)^(−),NO,and peroxynitrite to induce phototoxicity.By applying it to the 4T1 breast tumor model,JSK-BPT NPs achieved high-quality multimodal imaging of the vasculature and tumor regions in mice.Under the multimodal imaging guidance,the 4T1 tumor could be ablated completely after a single dose of JSK-BPT NPs and under the irradiation of an 808 nm laser.展开更多
The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.Howeve...The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.However,there is lack of systematic research on the mechanisms and influencing factors of fracture propagation in car-bonate rocks.This paper established models including karst cave models,single natural fracture-cave models,and multiple natural fracture-cave models based on the discrete lattice method.It thoroughly studied how geological and operational factors affect the fracture propagation and the connectivity of karst caves.The final step involved establishing a prototype well model and optimizing operation parameters.The research indicates that an increase in the Young's modulus and pore pressure of karst cave could facilitate hydraulic fracture connecting with caves.When the pore pressure is lower than that in the matrix,it will generate a repulsive effect on hydraulic fractures.The natural fracture along the hydraulic fracture path significantly facilitates the connection with caves.When the wellbore azimuth is less than 60℃,the fracture's diversion radius is small,and hydraulic fractures primarily connect with karst cave through natural fractures.When the wellbore azimuth exceeds 60℃,the fracture's diversion radius increases.Under the combined action of hydraulic fractures and natural fractures,the stimulated volume of the karst cave noticeably increases.Under the same liquid volume,increasing the injection rate could enhance the cave stimulated volume.Combining the findings from numerical simulation studies resulted in the development of a diagram that depicts the connectivity of karst caves,providing valuable insight for hydraulic fracturing operations in carbonate reservoirs.展开更多
基金support of the National Natural Science Foundation of China(Grant No.52474069)the National Natural Science Foundation of China(No.52104060).
文摘Proppant flowback in the post-fracturing flowback period not only reduces the fracture conductivity but also damages equipment.Due to the current lack of experimental or numerical simulation methods for proppant flowback in partial closure fracture,the mechanisms and patterns of proppant flowback remain unclear.This makes it difficult to predict the risks of proppant flowback,leaving flowback program design without theoretical guidance and resulting in high uncertainty in prevention effectiveness.This paper has further modified the CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)coupling interface by introducing fracture closure pressure into the particle motion equation.Based on the dynamic mesh,the fracture width in the CFD model is adjusted in real time to establish a numerical simulation method that considers fracture closure and synchronous changes in the flow field.By establishing flow similarity at the perforations,a near-wellbore flow field is created in the scaled model that is representative of field conditions,ensuring the practical value of the experimental results.Based on proppant particle force analysis during flowback,we investigated the impact of closure pressure,friction coefficient,perforation parameters,fracture dip angle,proppant particle size combination on proppant flowback.The research indicates that the existence of a threshold closure pressure arises from the competition between the lateral force(driving flowback)exerted by fracture closure on particles and the frictional force(resisting flowback)acting on particles.Below this threshold,increasing closure pressure enhances near-wellbore proppant flowback;above this threshold,increased closure pressure reduces proppant flowback.This threshold value is determined to be 1 MPa under the simulation conditions of this paper.The friction coefficient between particles and the fracture wall has greater impact on particle flowback than the friction coefficient between particles.In the vertical direction of the fracture,flowback is more probable for particles above the perforation.There is higher risk of particle flowback in horizontal fractures.The lateral distribution of large and small particles is more effective in preventing flowback than the vertical distribution.In the horizontal direction,particles nearer to the perforation have a higher probability of flowback.Strategies for proppant flowback control:the flow rate should be kept low initially,and then increased after the bottomhole pressure has been appropriately reduced;perforations should be placed in the upper part of the reservoir(vertical well);the sand concentration should not be increased in the later stages of fracturing to reduce the accumulation of proppant above the perforations;different size proppants should be injected in smaller sizes followed by larger sizes,with a slug of clean fluid in between to achieve a side-by-side placement of larger and smaller proppant,thereby mitigating proppant flowback.
基金support from Shenzhen Medical Research Fund(B2402042)National Natural Science Foundation of China(22274069 and 22304070)+1 种基金Shenzhen Science and Technology Program project(JCYJ20240813094504007 and JCYJ20210324104007020)Guangdong Provincial Key Laboratory of Advanced Biomaterials(2022B1212010003).
文摘Near-infrared Ⅱ(NIR-Ⅱ)fluorescent nanoparticles(NPs)based on aggregation-induced emission(AIE)have attracted significant attention due to theirmultimodal imaging capabilities aswell as the combined photothermal and photodynamic therapeutic effects in cancer therapy.Reported herein is the rational designed AIE molecule(BPT),via incorporating phenothiazine units with strong electron-donating and reactive oxygen species(ROS)generation capabilities into the classical AIE scaffold tetraphenylethylene,further coupled with a strong electron-acceptor named benzo[1,2-c:4,5-c’]bis[1,2,5]thiadiazole.The BPT NPs exhibited maximum NIR-Ⅱ fluorescence emission at 1083 nm,a fluorescence quantum yield of 1.53%,photothermal conversion efficiency of 63%,and photoacoustic imaging capabilities,alongside considerable type I ROS generation ability.Additionally,when a kind of nitric oxide(NO)donor named O_(2)-(2,4-dinitrophenyl)1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate(JSK)was incorporated,the corresponding JSK-BPT NPs could generate O_(2)^(−),NO,and peroxynitrite to induce phototoxicity.By applying it to the 4T1 breast tumor model,JSK-BPT NPs achieved high-quality multimodal imaging of the vasculature and tumor regions in mice.Under the multimodal imaging guidance,the 4T1 tumor could be ablated completely after a single dose of JSK-BPT NPs and under the irradiation of an 808 nm laser.
基金supported by the Natural Science Foundation of China(Grant No.52074332).
文摘The karst cave serves as the primary storage space in carbonate reservoirs.Simultaneously connecting multiple karst caves through hydraulic fracturing is key to the efficient development of carbonate reservoirs.However,there is lack of systematic research on the mechanisms and influencing factors of fracture propagation in car-bonate rocks.This paper established models including karst cave models,single natural fracture-cave models,and multiple natural fracture-cave models based on the discrete lattice method.It thoroughly studied how geological and operational factors affect the fracture propagation and the connectivity of karst caves.The final step involved establishing a prototype well model and optimizing operation parameters.The research indicates that an increase in the Young's modulus and pore pressure of karst cave could facilitate hydraulic fracture connecting with caves.When the pore pressure is lower than that in the matrix,it will generate a repulsive effect on hydraulic fractures.The natural fracture along the hydraulic fracture path significantly facilitates the connection with caves.When the wellbore azimuth is less than 60℃,the fracture's diversion radius is small,and hydraulic fractures primarily connect with karst cave through natural fractures.When the wellbore azimuth exceeds 60℃,the fracture's diversion radius increases.Under the combined action of hydraulic fractures and natural fractures,the stimulated volume of the karst cave noticeably increases.Under the same liquid volume,increasing the injection rate could enhance the cave stimulated volume.Combining the findings from numerical simulation studies resulted in the development of a diagram that depicts the connectivity of karst caves,providing valuable insight for hydraulic fracturing operations in carbonate reservoirs.
