During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomen...During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomenon,a numerical simulation framework of the finite volume method and transient embedded discrete fracture model is proposed to establish a new constitutive model that links poroelastoplastic deformation,adsorption-induced swelling,and aperture compression.From this model,anisotropic permeability tensors were derived to further achieve the simulation of coevolution.Meanwhile,our permeability model was verified against the measured permeability data,and the history match of the numerical model showed better results where the mismatch was less than 5%.The results indicate that(1)the long-term permeability evolution clearly showed the competitive effects of multiple deformation mechanisms,which involves three stages:compaction-dominated decline,adsorption-dominated rebound,and creep-controlled loss.(2)The increased number of compressible cleats/fractures accelerated the initial permeability decline,while the increased desorption-induced strain promoted faster rebound and enhancement and higher viscosity coefficients enhanced the creep effect,which led to significant long-term permeability loss.(3)Massive hydraulic fracturing created a larger drainage area,accelerating methane desorption and causing sharp permeability rebound with reduced residual gas,which shows that the permeability remained higher than the initial values even after the extensive extraction via the fractured horizontal wells.The permeability evolution mechanisms displayed varying properties,such as coal rank and burial depth,and distinct characteristics.A precise understanding of multiple competitive stress effects is crucial for optimizing coalbed methane extraction techniques and improving recovery efficiency.展开更多
Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhyd...Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhydraulic-mechnical(THM)coupled fracture propagation model relying on the phase field method to simulate thermal shock-induced fracturing in the deep shale considering dynamic temperature conditions.The validity of this model is confirmed through comparison of experimental and numerical results concerning the THM-coupled stress field and thermal cracking.Special attention is paid to the interaction of thermal shock-induced fractures in deep shale that contains weak planes.The results indicate that thermal shock-induced stress significantly amplifies the tensile stress range and deteriorates rock strength,resulting in a multi-point failure pattern within a fracture.The thermal shock damage degree is closely related to the fracture cooling efficiency,suggesting that considering downhole temperature conditions in THM-coupled fracture stress field calculations is advisable.Thermal shock can activate pre-existing natural fractures and enhance the penetration ability of hydraulic fractures,thereby leading to a fracture network.展开更多
Stimulated shale reservoirs consist of kerogen,inorganic matter,secondary and hydraulic fractures.The dispersed distribution of kerogen within matrices and complex gas flow mechanisms make production evaluation challe...Stimulated shale reservoirs consist of kerogen,inorganic matter,secondary and hydraulic fractures.The dispersed distribution of kerogen within matrices and complex gas flow mechanisms make production evaluation challenging.Here we establish an analytical method that addresses kerogen-inorganic matter gas transfer,dispersed kerogen distribution,and complex gas flow mechanisms to facilitate evaluating gas production.The matrix element is defined as a kerogen core with an exterior inorganic sphere.Unlike most previous models,we merely use boundary conditions to describe kerogen-inorganic matter gas transfer without the instantaneous kerogen gas source term.It is closer to real inter-porosity flow conditions between kerogen and inorganic matter.Knudsen diffusion,surface diffusion,adsorption/desorption,and slip corrected flow are involved in matrix gas flow.Matrix-fracture coupling is realized by using a seven-region linear flow model.The model is verified against a published model and field data.Results reveal that inorganic matrices serve as a major gas source especially at early times.Kerogen provides limited contributions to production even under a pseudo-steady state.Kerogen properties’influence starts from the late matrix-fracture inter-porosity flow regime,while inorganic matter properties control almost all flow regimes except the early-mid time fracture linear flow regime.The contribution of different linear flow regions is also documented.展开更多
The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that o...The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.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
Based on the DEA-based Malmquist index method,the total factor productivity was calculated for 5 major banana production areas in 2003-2004,and it was further divided into technological progress and technical efficien...Based on the DEA-based Malmquist index method,the total factor productivity was calculated for 5 major banana production areas in 2003-2004,and it was further divided into technological progress and technical efficiency.The results show that the total factor productivity of banana industry in China was 1.3% in the sample period,mainly due to technological progress,the average growth rate was 2.6%,while the pure technical efficiency and scale efficiency was -0.1% and -1.2% respectively.The improvement of total factor productivity in banana industry in China relied mainly on technological progress,cultivation of new banana varieties,management of high quality cultivation,popularization and application of water conservation and fertilizer saving technology,and injury-free picking technologies.The pure technical efficiency and scale efficiency of banana production were negative,indicating that the management level of banana was not high.The effect of scale economy of this industry through agglomeration and consolidation is still to be practiced.Banana growers should promote the improvement of large scale and management level of the banana industry at the same time of promoting the technological progress.展开更多
During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter...During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.展开更多
There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,nar...There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,narrow channels,and strong horizontal and vertical heteroge-neity,however,conventional fracturing technologies cannot achieve the ideal stimulation effect here.In order to address this difficulty,this paper dissects the geology engineering characteristics of tight sandstone gas reservoirs in the western Sichuan Basin.Starting from the seepage mechanics theory,the concept of“multi-scale high-density”tight gas fracturing technology is put forward by fully referring to the experience of previous multi-round reservoir stimulation in the western Sichuan Basin and the idea of unconventional volume fracturing technology.In addition,its conceptual connotation,key technologies and implementation effects are illustrated.The following research results are obtained.First,the seepage characteristics make it necessary for the efficient production of tight gas reserves to increase fracture density and stimulated reservoir volume(SRV).Second,the“multi-scale high-density”fracturing technology emphasizes the rationality of high-density hydraulic fracture creation and the matching of multi-scale fractureflow capacity,and aims at establishing a multi-level fracture system with effective and steady gasflow in tight reservoirs through fracturing.Third,the“wide,dense,support,stable,and precise”fracturing technology is applied to improve single well production and estimated ultimate recovery(EUR).Fourth,the engineering practice of“multi-scale high-density”fracturing technology in the tight reservoirs of Jurassic Shaximiao Formation and Triassic Xujiahe Formation in the ZJ Gas Field realizes the average single well production rate of 15.6104 m3/d,which is 1.96 times higher than that before the stimulation.Obviously,it provides powerful support for the operation of the ZJ Gas Field into a giant gasfield with the reserves of 100 billion cubic meters.In conclusion,the formation of the concept and key technologies of“multi-scale high-density”fracturing technology effectively supports the efficient development of tight gas in the western Sichuan Basin and points out the following research direction of tight gas reservoir stimulation.The research results provide reference and guidance for the large-scale benefit development of tight gas in China.展开更多
During workover operations in high-pressure gas wells,heavy mud losses may occur,reducing gas production.Refracturing is an effective means to restore production.The influence of heavy mud loss on refracturing is stil...During workover operations in high-pressure gas wells,heavy mud losses may occur,reducing gas production.Refracturing is an effective means to restore production.The influence of heavy mud loss on refracturing is still unclear.In this paper,split core is designed to simulate the fractures of the initial transformation,transparent sand-filled pipe is designed to simulate the sand filled fractures,and the experiment of heavy mud leakage in artificial fractures under different conditions is carried out by using the displacement device,combined with CT scanning and pressure monitoring means.The influence of heavy mud loss on permeability of artificial fracture,repeated reconstruction construction pressure and flow channel configuration in artificial fracture is analyzed.The results show that workover heavy mud(WHM)loss has the greatest permeability damage to the proppant fracture packed with large particle size,up to 97%,and the fracture permeability damage of 40/70 mesh ceramsite packing is only 0.3%–0.7%.Slit core permeability damage is the least,and the decrease range is 10%–20%.The damage of matrix core permeability measured by gas is no less than 60%.Before and after the loss of WHM,the injection pressure increases significantly,up to 80 times.Combined with the CT scan results,it is found that after WHM loss,the nitrogen blowout and refracturing incompletely remove the pollution,and there is a“pollution cage”in the fracture,which is the main reason for the high construction pressure of refracturing and low production after refracturing.The research results provide theoretical basics for the refracturing of WHM loss wells.展开更多
Dear Editor,Generation of heterozygous genomes by hybridization between or within species can help maintain plant diversity and serve as a potential source of new species(Baek et al.,2018).Moreover,genomic heterozygos...Dear Editor,Generation of heterozygous genomes by hybridization between or within species can help maintain plant diversity and serve as a potential source of new species(Baek et al.,2018).Moreover,genomic heterozygosity is associated with genomic coadaptation,developmental stability,and heterosis.Accurate definition of alleles in haplotypes is necessary to precisely characterize allelic variation controlling agriculturally important traits(Shi et al.,2019).Currently,most released genomes have mosaic assembly of haplotypes due to random selection or collapse of alleles during genome assembly(Shi et al.,2019),which masked allelic variation and functional differentiation of divergent alleles in heterozygous species.展开更多
Hydraulic fracturing is the primary method used for oilfield stimulation,and the migration and settlement pattern of proppant plays a crucial role in the formation of high conductivity propping fractures in the reserv...Hydraulic fracturing is the primary method used for oilfield stimulation,and the migration and settlement pattern of proppant plays a crucial role in the formation of high conductivity propping fractures in the reservoir.This study summarizes two growth modes of sand dune:the‘overall longitudinal growth’mode and the‘push growth along fracture length direction’mode.To investigate these modes,a twophase velocity test is conducted using PIV,and the exposure difference is utilized to separate the tracer and track the single-phase velocity.By analyzing the slickwater flow field and proppant velocity field,the micro-motion mechanism behind the two dune growth modes is quantitatively examined.The results indicate that mode 1 growth of the sand dune occurs when a pump with a large mesh number,high polymer viscosity,and large displacement is used.On the other hand,mode 2 growth is observed when a pump with a small mesh number,low polymer viscosity,and small displacement is employed.It is important to note that there is no clear boundary for the migration and sedimentation mode of proppant,as they can transition into each other under certain conditions.These modes only exist during specific stages of sand dune growth.In the case of the‘backflow’pattern,the settlement of proppant is primarily influenced by the vortex structure of slickwater.Conversely,in the‘direct’pattern,the proppant is propelled forward by the drag of the fluid and settles due to its own gravity.Once the proppant placement reaches equilibrium,the direction of proppant velocity follows a normal distribution within 0°.This approach establishes a connection between the overall placement of the sand dune and the microscopic movement of the proppant and slickwater.Optimizing construction parameters during fracturing construction can enhance the effectiveness of distal proppant placement in fractures.展开更多
The diffusion of pore fluid pressures may create both spatial and temporal effective stress gradients that influence or control the development and evolution of fractures within rock masses. To better understand the c...The diffusion of pore fluid pressures may create both spatial and temporal effective stress gradients that influence or control the development and evolution of fractures within rock masses. To better understand the controls on fracturing behavior, numerical simulations are performed using a progressive fracture modeling approach that shares many of the same natural kinematic features in rocks, such as fracture growth, nucleation, and termination. First, the pinch-off breaking test is numerically performed to investigate the tensile failure of a rock specimen in a uniform pore pressure field. In this numerical simulation, both mechanical and hydrological properties of a suite of rocks are measured under simulated laboratory conditions. The complete tensional failure process of the rock specimen under pore pressure was reproduced. Second, a double-notched specimen is numerically extended to investigate how the water flow direction or pore pressure gradient influences the fracture growth. An exhaustive sensitivity study is conducted that examines the effects of varying both hydrological and mechanical boundary conditions. The simulation results indicate that local fluid pressure gradients strongly influence the state of stress in the solids and, thereby, fracture growth. Fracture and strength behavior is influenced not only by the pore pressure magnitude on a local scale around the fracture tip, but also by the orientation and distribution of pore pressure gradients on a global scale. Increasing the fracture growth rate increases the local model permeability and decreases the sample strength. The results of this study may provide useful information concerning the degree of hydrological and mechanical coupling action under geologic conditions.展开更多
Cardio-cerebrovascular disease(CCVD)is a major comorbidity of coronavirus disease 2019(COVID-19).However,the clinical characteristics and outcomes remain unclear.In this study,102 cases of COVID-19 from January 22,202...Cardio-cerebrovascular disease(CCVD)is a major comorbidity of coronavirus disease 2019(COVID-19).However,the clinical characteristics and outcomes remain unclear.In this study,102 cases of COVID-19 from January 22,2020 to March 26,2020 in Xixi Hospital of Hangzhou were included.Twenty cases had pre-existing CCVD.Results showed that compared with non-CCVD patients,those with CCVD are more likely to develop severe disease(15%versus 1%),and the proportion of pneumonia severity index grade IV was significantly higher(25%versus 3.6%).Computed tomography images demonstrated that the proportion of multiple lobe lesion involvement was significantly higher in the CCVD group than in the non-CCVD group(90%versus 63.4%).Compared with non-CCVD group,the levels of C-reactive protein,fibrinogen,D-dimer,and serum amyloid-A were higher,whereas the total protein and arterial partial Pa02 were lower in the CCVD group.Although no statistical difference was observed in the outcomes between groups,CCVD patients received more intensive comprehensive treatment to improve COVID-19 symptoms compared with non-CCVD patients.Integrated Chinese and Western medicine treatments have certain advantages in controlling the severe conversion rate and mortality of COVID-19.In addition,given that COVID-19 patients are usually related to coagulation disorders and thrombosis risk,the application of Chinese medicine in promoting blood circulation and removing stasis should be strengthened.展开更多
The brittleness index plays a significant role in the hydraulic fracturing design and wellbore stability analysis of shale reservoirs.Various brittleness indices have been proposed to characterize the brittleness of s...The brittleness index plays a significant role in the hydraulic fracturing design and wellbore stability analysis of shale reservoirs.Various brittleness indices have been proposed to characterize the brittleness of shale rocks,but almost all of them ignored the anisotropy of the brittleness index.Therefore,uniaxial compression testing integrated with geophysical logging was used to provide insights into the anisotropy of the brittleness index for Longmaxi shale,the presented method was utilized to assess brittleness index of Longmaxi shale formation for the interval of 3155e3175 m in CW-1 well.The results indicated that the brittleness index of Longmaxi shale showed a distinct anisotropy,and it achieved the minimum value at β=45°-60°.As the bedding angle increased,the observed brittleness index(BI_(2_β))decreased firstly and increased then,it achieved the lowest value at β=40°-60°,and it is consistent with the uniaxial compression testing results.Compared to the isotropic brittleness index(β=0°),the deviation of the anisotropic brittleness index ranged from 10%to 66.7%,in other words,the anisotropy of brittleness index cannot be ignored for Longmaxi shale.Organic matter content is one of the main intrinsic causes of shale anisotropy,and the anisotropy degree of the brittleness index generally increases with the increase in organic matter content.The present work is valuable for the assessment of anisotropic brittleness for hydraulic fracturing design and wellbore stability analysis.展开更多
During cementing operations involving cement slurry contamination,problems often occur due to the inaccurate calculation of the space fluid volume.This study,based on the turbulent dispersion theory,developed a minimu...During cementing operations involving cement slurry contamination,problems often occur due to the inaccurate calculation of the space fluid volume.This study,based on the turbulent dispersion theory,developed a minimum volume calculation model of spacer fluid to prevent cement slurry contamination.This model was used to analyze influence factors and practical calculations.The results indicated that the minimum volume of spacer fluid increase with the eccentricity of casing and injection rate and decrease with the density of cement slurry.Additionally,the better rheological properties of the cement slurry and spacer fluid would increase the volume of the spacer fluid.Furthermore,this model fitted actual field data better than other heat calculation models.展开更多
Backgroud:The outbreak of COVID-19 has brought unprecedented perils to human health and raised public health concerns in more than two hundred countries.Safe and effective treatment scheme is needed urgently.Objective...Backgroud:The outbreak of COVID-19 has brought unprecedented perils to human health and raised public health concerns in more than two hundred countries.Safe and effective treatment scheme is needed urgently.Objective:To evaluate the effects of integratedTCM and western medicine treatment scheme on COVID-19.Methods:A single-armed clinical trial was carried out in Hangzhou Xixi Hospital,an affiliated hospital with Zhejiang Chinese Medical University.102 confirmed cases were screened out from 725 suspected cases and 93 of them were treated with integrated TCM and western medicine treatment scheme.Results:83 cases were cured,5 cases deteriorated,and 5 cases withdrew from the study.No deaths were reported.The mean relief time of fever,cough,diarrhea,and fatigue were(4.78±4.61)days,(7.22±4.99)days,(5.28±3.39)days,and(5.28±3.39)days,respectively.It took(14.84±5.50)days for SARS-CoV-2 by nucleic acid amplification-based testing to turn negative.Multivariable cox regression analysis revealed that age,BMI,PISCT,BPC,AST,CK,BS,and UPRO were independent risk factors for COVID-19 treatment.Conclusion:Our study suggested that integrated TCM and western medicine treatment scheme was effective for COVID-19.展开更多
基金support of the National Natural Science Foundation of China(U23B6004 and 52404045)the CAST Young Talent Support Program,Doctoral Student Special Project.
文摘During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomenon,a numerical simulation framework of the finite volume method and transient embedded discrete fracture model is proposed to establish a new constitutive model that links poroelastoplastic deformation,adsorption-induced swelling,and aperture compression.From this model,anisotropic permeability tensors were derived to further achieve the simulation of coevolution.Meanwhile,our permeability model was verified against the measured permeability data,and the history match of the numerical model showed better results where the mismatch was less than 5%.The results indicate that(1)the long-term permeability evolution clearly showed the competitive effects of multiple deformation mechanisms,which involves three stages:compaction-dominated decline,adsorption-dominated rebound,and creep-controlled loss.(2)The increased number of compressible cleats/fractures accelerated the initial permeability decline,while the increased desorption-induced strain promoted faster rebound and enhancement and higher viscosity coefficients enhanced the creep effect,which led to significant long-term permeability loss.(3)Massive hydraulic fracturing created a larger drainage area,accelerating methane desorption and causing sharp permeability rebound with reduced residual gas,which shows that the permeability remained higher than the initial values even after the extensive extraction via the fractured horizontal wells.The permeability evolution mechanisms displayed varying properties,such as coal rank and burial depth,and distinct characteristics.A precise understanding of multiple competitive stress effects is crucial for optimizing coalbed methane extraction techniques and improving recovery efficiency.
基金paper is funded by the CNOOC Science and Technology Project(KJGG2022-0701)the National Natural Science Foundation of China(51904258,51874250).
文摘Thermal shock damage in deep shale hydraulic fracturing can impact fracture propagation behaviors,potentially leading to the formation of complex fractures and enhancing gas recovery.This study introduces a thermalhydraulic-mechnical(THM)coupled fracture propagation model relying on the phase field method to simulate thermal shock-induced fracturing in the deep shale considering dynamic temperature conditions.The validity of this model is confirmed through comparison of experimental and numerical results concerning the THM-coupled stress field and thermal cracking.Special attention is paid to the interaction of thermal shock-induced fractures in deep shale that contains weak planes.The results indicate that thermal shock-induced stress significantly amplifies the tensile stress range and deteriorates rock strength,resulting in a multi-point failure pattern within a fracture.The thermal shock damage degree is closely related to the fracture cooling efficiency,suggesting that considering downhole temperature conditions in THM-coupled fracture stress field calculations is advisable.Thermal shock can activate pre-existing natural fractures and enhance the penetration ability of hydraulic fractures,thereby leading to a fracture network.
基金supported by the Australian Research Council under Grant DP200101293UWA China Scholarshipsthe China Scholarship Council(CSC No.201707970011)。
文摘Stimulated shale reservoirs consist of kerogen,inorganic matter,secondary and hydraulic fractures.The dispersed distribution of kerogen within matrices and complex gas flow mechanisms make production evaluation challenging.Here we establish an analytical method that addresses kerogen-inorganic matter gas transfer,dispersed kerogen distribution,and complex gas flow mechanisms to facilitate evaluating gas production.The matrix element is defined as a kerogen core with an exterior inorganic sphere.Unlike most previous models,we merely use boundary conditions to describe kerogen-inorganic matter gas transfer without the instantaneous kerogen gas source term.It is closer to real inter-porosity flow conditions between kerogen and inorganic matter.Knudsen diffusion,surface diffusion,adsorption/desorption,and slip corrected flow are involved in matrix gas flow.Matrix-fracture coupling is realized by using a seven-region linear flow model.The model is verified against a published model and field data.Results reveal that inorganic matrices serve as a major gas source especially at early times.Kerogen provides limited contributions to production even under a pseudo-steady state.Kerogen properties’influence starts from the late matrix-fracture inter-porosity flow regime,while inorganic matter properties control almost all flow regimes except the early-mid time fracture linear flow regime.The contribution of different linear flow regions is also documented.
基金supported by the National Natural Science Foundation of China(Grant No.52022087).
文摘The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.
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 Industrial Economic Post of National Banana Industrial Technological System of the Ministry of Agriculture(CARS-32-10)
文摘Based on the DEA-based Malmquist index method,the total factor productivity was calculated for 5 major banana production areas in 2003-2004,and it was further divided into technological progress and technical efficiency.The results show that the total factor productivity of banana industry in China was 1.3% in the sample period,mainly due to technological progress,the average growth rate was 2.6%,while the pure technical efficiency and scale efficiency was -0.1% and -1.2% respectively.The improvement of total factor productivity in banana industry in China relied mainly on technological progress,cultivation of new banana varieties,management of high quality cultivation,popularization and application of water conservation and fertilizer saving technology,and injury-free picking technologies.The pure technical efficiency and scale efficiency of banana production were negative,indicating that the management level of banana was not high.The effect of scale economy of this industry through agglomeration and consolidation is still to be practiced.Banana growers should promote the improvement of large scale and management level of the banana industry at the same time of promoting the technological progress.
文摘During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.
基金supported by the key project of the United Foun-dation of National NaturalScience Foundation of China“Basic Research on Volumetric Acid Fracturing of Deep Sulfur-bearing Carbonate Gas Reservoirs in Sichuan Basin”(No.U21A20105)CNPC Science and Technology Innovation Project"Research on the Mechanism of Complex Fracture Propagation and Control Measures of Temporary Plugging Fracturing of Shale Gas Reservoir"(No.2020D-5007-0208).
文摘There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,narrow channels,and strong horizontal and vertical heteroge-neity,however,conventional fracturing technologies cannot achieve the ideal stimulation effect here.In order to address this difficulty,this paper dissects the geology engineering characteristics of tight sandstone gas reservoirs in the western Sichuan Basin.Starting from the seepage mechanics theory,the concept of“multi-scale high-density”tight gas fracturing technology is put forward by fully referring to the experience of previous multi-round reservoir stimulation in the western Sichuan Basin and the idea of unconventional volume fracturing technology.In addition,its conceptual connotation,key technologies and implementation effects are illustrated.The following research results are obtained.First,the seepage characteristics make it necessary for the efficient production of tight gas reserves to increase fracture density and stimulated reservoir volume(SRV).Second,the“multi-scale high-density”fracturing technology emphasizes the rationality of high-density hydraulic fracture creation and the matching of multi-scale fractureflow capacity,and aims at establishing a multi-level fracture system with effective and steady gasflow in tight reservoirs through fracturing.Third,the“wide,dense,support,stable,and precise”fracturing technology is applied to improve single well production and estimated ultimate recovery(EUR).Fourth,the engineering practice of“multi-scale high-density”fracturing technology in the tight reservoirs of Jurassic Shaximiao Formation and Triassic Xujiahe Formation in the ZJ Gas Field realizes the average single well production rate of 15.6104 m3/d,which is 1.96 times higher than that before the stimulation.Obviously,it provides powerful support for the operation of the ZJ Gas Field into a giant gasfield with the reserves of 100 billion cubic meters.In conclusion,the formation of the concept and key technologies of“multi-scale high-density”fracturing technology effectively supports the efficient development of tight gas in the western Sichuan Basin and points out the following research direction of tight gas reservoir stimulation.The research results provide reference and guidance for the large-scale benefit development of tight gas in China.
基金supported by the National Natural Science Foundation Enterprise Innovation and Development Joint fund of China(No.U23B6004)。
文摘During workover operations in high-pressure gas wells,heavy mud losses may occur,reducing gas production.Refracturing is an effective means to restore production.The influence of heavy mud loss on refracturing is still unclear.In this paper,split core is designed to simulate the fractures of the initial transformation,transparent sand-filled pipe is designed to simulate the sand filled fractures,and the experiment of heavy mud leakage in artificial fractures under different conditions is carried out by using the displacement device,combined with CT scanning and pressure monitoring means.The influence of heavy mud loss on permeability of artificial fracture,repeated reconstruction construction pressure and flow channel configuration in artificial fracture is analyzed.The results show that workover heavy mud(WHM)loss has the greatest permeability damage to the proppant fracture packed with large particle size,up to 97%,and the fracture permeability damage of 40/70 mesh ceramsite packing is only 0.3%–0.7%.Slit core permeability damage is the least,and the decrease range is 10%–20%.The damage of matrix core permeability measured by gas is no less than 60%.Before and after the loss of WHM,the injection pressure increases significantly,up to 80 times.Combined with the CT scan results,it is found that after WHM loss,the nitrogen blowout and refracturing incompletely remove the pollution,and there is a“pollution cage”in the fracture,which is the main reason for the high construction pressure of refracturing and low production after refracturing.The research results provide theoretical basics for the refracturing of WHM loss wells.
基金supported by the National Key Research and Development Program of China(grant no.2019YFD1000500)the 2020 Research Program of Sanya Yazhou Bay Science and Technology City(grant no.SKJC-2020-02-002)+2 种基金the Central Public-Interest Scientific Institution Basal Research Fund for Chinese Academy of Tropical Agricultural Sciences(grant nos.1630012019009,1630052016005,1630052016006,1630052017021,and 1630052019023)the Central Public-Interest Scientific Institution Basal Research Fund for Innovative Research Team Program of CATAS(grant nos.17CXTD-28 and 1630052017017)the ear-marked fund for Modern Agro-industry Technology Research System(grant no.nycytx-11).
文摘Dear Editor,Generation of heterozygous genomes by hybridization between or within species can help maintain plant diversity and serve as a potential source of new species(Baek et al.,2018).Moreover,genomic heterozygosity is associated with genomic coadaptation,developmental stability,and heterosis.Accurate definition of alleles in haplotypes is necessary to precisely characterize allelic variation controlling agriculturally important traits(Shi et al.,2019).Currently,most released genomes have mosaic assembly of haplotypes due to random selection or collapse of alleles during genome assembly(Shi et al.,2019),which masked allelic variation and functional differentiation of divergent alleles in heterozygous species.
基金prepared under the auspices of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation at Southwest Petroleum UniversityAnd supported by National Nat-ural Science Foundation of China(U21A20105,51874250).
文摘Hydraulic fracturing is the primary method used for oilfield stimulation,and the migration and settlement pattern of proppant plays a crucial role in the formation of high conductivity propping fractures in the reservoir.This study summarizes two growth modes of sand dune:the‘overall longitudinal growth’mode and the‘push growth along fracture length direction’mode.To investigate these modes,a twophase velocity test is conducted using PIV,and the exposure difference is utilized to separate the tracer and track the single-phase velocity.By analyzing the slickwater flow field and proppant velocity field,the micro-motion mechanism behind the two dune growth modes is quantitatively examined.The results indicate that mode 1 growth of the sand dune occurs when a pump with a large mesh number,high polymer viscosity,and large displacement is used.On the other hand,mode 2 growth is observed when a pump with a small mesh number,low polymer viscosity,and small displacement is employed.It is important to note that there is no clear boundary for the migration and sedimentation mode of proppant,as they can transition into each other under certain conditions.These modes only exist during specific stages of sand dune growth.In the case of the‘backflow’pattern,the settlement of proppant is primarily influenced by the vortex structure of slickwater.Conversely,in the‘direct’pattern,the proppant is propelled forward by the drag of the fluid and settles due to its own gravity.Once the proppant placement reaches equilibrium,the direction of proppant velocity follows a normal distribution within 0°.This approach establishes a connection between the overall placement of the sand dune and the microscopic movement of the proppant and slickwater.Optimizing construction parameters during fracturing construction can enhance the effectiveness of distal proppant placement in fractures.
文摘The diffusion of pore fluid pressures may create both spatial and temporal effective stress gradients that influence or control the development and evolution of fractures within rock masses. To better understand the controls on fracturing behavior, numerical simulations are performed using a progressive fracture modeling approach that shares many of the same natural kinematic features in rocks, such as fracture growth, nucleation, and termination. First, the pinch-off breaking test is numerically performed to investigate the tensile failure of a rock specimen in a uniform pore pressure field. In this numerical simulation, both mechanical and hydrological properties of a suite of rocks are measured under simulated laboratory conditions. The complete tensional failure process of the rock specimen under pore pressure was reproduced. Second, a double-notched specimen is numerically extended to investigate how the water flow direction or pore pressure gradient influences the fracture growth. An exhaustive sensitivity study is conducted that examines the effects of varying both hydrological and mechanical boundary conditions. The simulation results indicate that local fluid pressure gradients strongly influence the state of stress in the solids and, thereby, fracture growth. Fracture and strength behavior is influenced not only by the pore pressure magnitude on a local scale around the fracture tip, but also by the orientation and distribution of pore pressure gradients on a global scale. Increasing the fracture growth rate increases the local model permeability and decreases the sample strength. The results of this study may provide useful information concerning the degree of hydrological and mechanical coupling action under geologic conditions.
基金This work was supported by the National Natural Science Foundation of China(No.81930111)Zhejiang Province High-level Talents Project(No.2019R51002).
文摘Cardio-cerebrovascular disease(CCVD)is a major comorbidity of coronavirus disease 2019(COVID-19).However,the clinical characteristics and outcomes remain unclear.In this study,102 cases of COVID-19 from January 22,2020 to March 26,2020 in Xixi Hospital of Hangzhou were included.Twenty cases had pre-existing CCVD.Results showed that compared with non-CCVD patients,those with CCVD are more likely to develop severe disease(15%versus 1%),and the proportion of pneumonia severity index grade IV was significantly higher(25%versus 3.6%).Computed tomography images demonstrated that the proportion of multiple lobe lesion involvement was significantly higher in the CCVD group than in the non-CCVD group(90%versus 63.4%).Compared with non-CCVD group,the levels of C-reactive protein,fibrinogen,D-dimer,and serum amyloid-A were higher,whereas the total protein and arterial partial Pa02 were lower in the CCVD group.Although no statistical difference was observed in the outcomes between groups,CCVD patients received more intensive comprehensive treatment to improve COVID-19 symptoms compared with non-CCVD patients.Integrated Chinese and Western medicine treatments have certain advantages in controlling the severe conversion rate and mortality of COVID-19.In addition,given that COVID-19 patients are usually related to coagulation disorders and thrombosis risk,the application of Chinese medicine in promoting blood circulation and removing stasis should be strengthened.
基金supported by the post-doctoral project of Petrochina Southwest Oil&Gas Field Company“Research on Deep Shale Geomechanics and Effective Fracturing Factors”(Grant No.20210302-31)the Program of Introducing Talents of Discipline to Chinese Universities(111 Plan)(Grant No.D18016)+2 种基金the Sichuan Science and Technology Program(Grant No.2020JDJQ0055)the Nanchong-SWPU Science and Technology Strategic Cooperation Foundation(Grant No.SXHZ033)the Youth Scientific and Technological Innovation Team Foundation of SWPU(Grant No.2019CXTD09).
文摘The brittleness index plays a significant role in the hydraulic fracturing design and wellbore stability analysis of shale reservoirs.Various brittleness indices have been proposed to characterize the brittleness of shale rocks,but almost all of them ignored the anisotropy of the brittleness index.Therefore,uniaxial compression testing integrated with geophysical logging was used to provide insights into the anisotropy of the brittleness index for Longmaxi shale,the presented method was utilized to assess brittleness index of Longmaxi shale formation for the interval of 3155e3175 m in CW-1 well.The results indicated that the brittleness index of Longmaxi shale showed a distinct anisotropy,and it achieved the minimum value at β=45°-60°.As the bedding angle increased,the observed brittleness index(BI_(2_β))decreased firstly and increased then,it achieved the lowest value at β=40°-60°,and it is consistent with the uniaxial compression testing results.Compared to the isotropic brittleness index(β=0°),the deviation of the anisotropic brittleness index ranged from 10%to 66.7%,in other words,the anisotropy of brittleness index cannot be ignored for Longmaxi shale.Organic matter content is one of the main intrinsic causes of shale anisotropy,and the anisotropy degree of the brittleness index generally increases with the increase in organic matter content.The present work is valuable for the assessment of anisotropic brittleness for hydraulic fracturing design and wellbore stability analysis.
基金The financial support of“Study on tight clastic rock completion and reservoir reconstruction technology in Sichuan Basin”(2016ZX05002-004-006)is greatly acknowledged.
文摘During cementing operations involving cement slurry contamination,problems often occur due to the inaccurate calculation of the space fluid volume.This study,based on the turbulent dispersion theory,developed a minimum volume calculation model of spacer fluid to prevent cement slurry contamination.This model was used to analyze influence factors and practical calculations.The results indicated that the minimum volume of spacer fluid increase with the eccentricity of casing and injection rate and decrease with the density of cement slurry.Additionally,the better rheological properties of the cement slurry and spacer fluid would increase the volume of the spacer fluid.Furthermore,this model fitted actual field data better than other heat calculation models.
基金This Research was Supported by Zhejiang Provincial Natural Science Foundation of China‘Emergency Prevention and Treatment of COVID-19′,Under Grated NO.LEZ20H190001 and COVID-19 prevention and control special scientific research project of Hangzhou Science and Tech-nology Bureau,China.
文摘Backgroud:The outbreak of COVID-19 has brought unprecedented perils to human health and raised public health concerns in more than two hundred countries.Safe and effective treatment scheme is needed urgently.Objective:To evaluate the effects of integratedTCM and western medicine treatment scheme on COVID-19.Methods:A single-armed clinical trial was carried out in Hangzhou Xixi Hospital,an affiliated hospital with Zhejiang Chinese Medical University.102 confirmed cases were screened out from 725 suspected cases and 93 of them were treated with integrated TCM and western medicine treatment scheme.Results:83 cases were cured,5 cases deteriorated,and 5 cases withdrew from the study.No deaths were reported.The mean relief time of fever,cough,diarrhea,and fatigue were(4.78±4.61)days,(7.22±4.99)days,(5.28±3.39)days,and(5.28±3.39)days,respectively.It took(14.84±5.50)days for SARS-CoV-2 by nucleic acid amplification-based testing to turn negative.Multivariable cox regression analysis revealed that age,BMI,PISCT,BPC,AST,CK,BS,and UPRO were independent risk factors for COVID-19 treatment.Conclusion:Our study suggested that integrated TCM and western medicine treatment scheme was effective for COVID-19.
