SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment,the supports were then used to load the active phase Cr Oxthrough a conventional impregnation method.The...SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment,the supports were then used to load the active phase Cr Oxthrough a conventional impregnation method.The resulting catalysts were characterized by small/wide angle XRD,N_(2) adsorption/desorption,FT-IR,TEM-EDX,XPS,TPR and CO_(2)-TPD to study the feature of structure,surface chemical state,redox and basicity.It was found from these results that the metal species could be well dispersed on catalysts with larger pore size.Cr^(6+)species could enter into the framework by substituting the Si atoms of SBA-15,and Cr^(3+)mainly exist on extra framework.Pore size had profound effects on reducibility,surface composition and basicity.Cr^(6+)species were necessary to activate the C-H bonds of alkanes,while the basicity played an important role in activating C-O bonds of CO_(2).The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO_(2).展开更多
In this work, the morphologies and pore structures of a series of corncob-derived activated carbons and zeolite templated carbon with ultrahigh surface area were carefully investigated by SEM, HRTEM and N2-sorption ch...In this work, the morphologies and pore structures of a series of corncob-derived activated carbons and zeolite templated carbon with ultrahigh surface area were carefully investigated by SEM, HRTEM and N2-sorption characterization technologies. The high-pressure hydrogen uptake performance was analyzed using standard Pressure-Composition-Temperature apparatus in order to study the pore size effects on hydrogen uptake. These as-obtained porous carbons showed different characteristics of pore size distribution as well as specific surface area. The results indicate that the most effective pores for adsorbing hydrogen depended on the storage pressure. These ultramicropores （0.65-0.85 nm） could be the most effective pores on excess H2 uptake at 1 bar, however, micropores （0.85-2 nm） would play a more important role in excess H2 uptake at higher pressure at 77 K. At room temperature, pore size effects on H2 uptake capacity were very weak. Both specific surface area and total pore volume play more important roles than pore size for H2 uptake at room temperature, which was clearly different from that at 77 K. For applications in future, the corncob-derived activated carbons can be more available than zeolite templated carbons at 77 K. Element doping enhanced hydrogen uptake could be main research direction for improving H2 uptake capacity at room temperature.展开更多
A novel negative thermal expansion(NTE) material NdMnO_(3) was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO_(3) were in...A novel negative thermal expansion(NTE) material NdMnO_(3) was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO_(3) were investigated by variable temperature X-ray diffraction(XRD), scanning electron microscope(SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O' phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO_(3) shows negative thermal expansion of-4.7×10^(-6)/K. As temperature increases, the ceramic NdMnO_(3) presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is-18.88×10^(-6)/K. The physical mechanism of NTE is discussed and clarified through experiments.展开更多
Coke is an important medium for connecting reaction and regeneration of the methanol to propylene process on the ZSM5 catalyst.Coke grows in the meso and macro pores,it gradually worsens the diffusion inside the catal...Coke is an important medium for connecting reaction and regeneration of the methanol to propylene process on the ZSM5 catalyst.Coke grows in the meso and macro pores,it gradually worsens the diffusion inside the catalyst particle.Furthermore,pore plugging is inevitable which causes the deactivation of ZSM5 catalyst.However,current continuum model cannot reflect the changes in pore structure with clear physical concepts.A discrete model that is verified by the carbon deposition experiments is introduced to indicate the behavior of pore plugging effects.Results show that the pore plugging has a significant effect on the performance of the catalyst.The time varying profile of effectiveness factor is obtained,indicating a regular reduction with the increase of the pore plugging effect.Spatial distributions of pore size that would significantly enhance the plugging effect are also identified.展开更多
A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential meth...A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential method.All types of pores are simultaneously introduced to the composite during the differential iteration process according to the ratio of their volume fractions.Based on this model,the effects of pore structures on predicted pore-pressure in carbonates were analyzed.Calculation results indicate that cracks with low pore aspect ratios lead to pore-pressure overestimation which results in lost circulation and reservoir damage.However,moldic pores and vugs with high pore aspect ratios lead to pore-pressure underestimation which results in well kick and even blowout.The pore-pressure deviation due to cracks and moldic pores increases with an increase in porosity.For carbonates with complex pore structures,adopting conventional pore-pressure prediction methods and casing program designs will expose the well drilling engineering to high uncertainties.Velocity prediction models considering the influence of pore structure need to be built to improve the reliability and accuracy of pore-pressure prediction in carbonates.展开更多
To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil r...To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil recovery of SP flooding was investigated at the pore, core and field scales through conducting experiments on natural core samples with three typical types of pore structures. First, the in-situ nuclear magnetic resonance core flooding test was carried out to capture the remaining oil variation features in the water flooding and SP flooding through these three types of cores. Subsequently, at the core scale, displacement characteristics and performances of water flooding and SP flooding in these three types of cores were evaluated based on the full-size core flooding tests. Finally, at the field scale, production characteristics of SP flooding in the bimodal sandstone reservoir and multimodal conglomerate reservoir were compared using the actual field production data. The results show: as the pore structure gets more and more complex, the water flooding performance gets poorer, but the incremental recovery factor by SP flooding gets higher;the SP flooding can enhance the producing degree of oil in 1-3 μm pores in the unimodal and bimodal core samples, while it produces largely oil in medium and large pores more than 3 μm in pore radius in the multimodal core sample. The core flooding test using full-size core sample demonstrates that the injection of SP solution can significantly raise up the displacement pressure of the multimodal core sample, and greatly enhance recovery factor by emulsifying the remaining oil and enlarging swept volume. Compared with the sandstone reservoir, the multimodal conglomerate reservoir is more prone to channeling. With proper profile control treatments to efficiently enlarge the microscopic and macroscopic swept volumes, SP flooding in the conglomerate reservoir can contribute to lower water cuts and longer effective durations.展开更多
The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qi...The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qianjiang depression,were analyzed.A double mercury injection method was used to distinguish between invalid and effective connected pores.The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were identified by comparing pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections.The results show that less than 50%of the total connected pores in the Eq34-10 cyclothem samples are effective.The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies.The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15 nm.In Well BYY2,residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10-200 nm,and in bulk argillaceous dolomite facies,it was mainly concentrated at 60-300 nm.The throats of hydrocarbon-retaining pores can be 5 nm or even smaller,but pores with movable shale oil in the well were found to have throat sizes greater than 40 nm.Excluding the influence of differences in wettability,the movability of shale oil is mainly affected by differences in lithofacies,the degree of pore deformation caused by diagenesis,the complexity of pore structures,and the connectivity of pore throats.Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.展开更多
The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas re...The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas reservoirs,do not take the unconnected pores into account,which impacts the evaluation accuracy of reservoir pore effectiveness.To solve this problem,this paper took the shale of Lower Silurian Longmaxi Formation in the southern Sichuan Basin as the research object to carry out experiments on core porosity,centrifugal+gradual drying NMR after saturated with brine and NMR freezeethaw using plunger samples and crushed samples to analyze the volume,main development location and main pore size distribution range of unconnected pores.Then,the pore systems were classified,and the lower limit of effective pore size of connected gas-bearing pores was determined.Finally,the total pore effectiveness of shale gas reservoirs was evaluated,and the influence of unconnected pores on the development of shale gas was discussed.And the following research results were obtained.First,there are a large number of unconnected pores in the shale gas reservoirs of the study area,accounting for 30.23%.Most of them are mainly developed in organic matters and a few are developed in clay minerals.The distribution of pore size ranges from 5 nm to 30 nm.Second,T_(2)cut-off value of clay bound water in the shale gas reservoirs of the study area is 0.26 ms,whose corresponding pore size is 5.35 nm,which is the lower limit of the effective pore size.Third,large-scale hydraulic fracturing can improve the unconnected pores with the size more than 5.35 nm,so effective development of shale gas will be realized.Fourth,after hydraulic fracturing stimulation,the unconnected pores can increase the storage space of fracturing fluid in the matrix,absorb the fracturing fluid in the fractures,replace the shale gas in the pores and promote the automatic alleviation of water lock in shale gas reservoirs,so the single-well shale gas production will be increased.In conclusion,fluid occurrence and pore system in shale pores can be quantitatively divided by means of centrifugal+gradual temperature drying method combined with NMR experiments,mobile water and capillary bound water can be determined by the high speed centrifugal+NMR experiments,and capillary bound water and clay bound water can be determined by the gradual drying t NMR experiments.展开更多
Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure a...Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for both the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are both the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure.展开更多
In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture a...In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture and pore structure features of the strata, and identified the main channels which govern the permeability and water-resisting ability of the strata. The permeability of the upper, central and lower strata shows as 2.0504 × 10^-3-2.782762× 10^-3, 4.1092 × 10^-3 -7.3387 × 10^-3 and 2.0891 ×10^-3-3.2705 × 10-3 μm^2, respectively, and porosity of that is 0.6786-0.9197%, 0.3109-0.3951% and 0.9829-1.8655%, respectively. The results indicate that： （I） the main channels of the relative water-resisting layer are the pore throats with a diameter more than 6 μm; （2） the major proportion of pore throats in the vertical flow channel and the permeability first increases and then sharply decreases; （3） the fractures occurring from the top to 20 m in depth of the strata were filled and there occurred almost no fracture under the depth of 40 m; and （4） the ratio of turning point of the main flow channel in the strata on top of Ordovician can be used to confirm the thickness of filled water-resisting lavers.展开更多
Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:...Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:(1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation,(2) hydraulic drained and undrained boundaries, and(3) heating from ambient temperature up to 90℃-120℃ and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.展开更多
It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on th...It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method （FEM） and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.展开更多
Physical mechanisms and influencing factors on the effective stress coefficient for rock/soil-like porous materials are investigated, based on which equivalent connectivity index is proposed. The equivalent connectivi...Physical mechanisms and influencing factors on the effective stress coefficient for rock/soil-like porous materials are investigated, based on which equivalent connectivity index is proposed. The equivalent connectivity index, relying on the meso-scale structure of porous material and the property of liquid, denotes the connectivity of pores in Representative Element Area （REA）. If the conductivity of the porous material is anisotropic, the equivalent connectivity index is a second order tensor. Based on the basic theories of continuous mechanics and tensor analysis, relationship between area porosity and volumetric porosity of porous materials is deduced. Then a generalized expression, describing the relation between effective stress coefficient tensor and equivalent connectivity tensor of pores, is proposed, and the expression can be applied to isotropic media and also to anisotropic materials. Furthermore, evolution of porosity and equivalent connectivity index of the pore are studied in the strain space, and the method to determine the corresponding functions in expressions above is proposed using genetic algorithm and genetic programming. Two applications show that the results obtained by the method in this paper perfectly agree with the test data. This paper provides an important theoretical support to the coupled hydro-mechanical research.展开更多
基金financial supports from National Natural Science Foundation of China(No.21603153)Science and Technology Department of Sichuan Province(No.2016HH0026)the Fundamental Research Funds for the Central Universities(No.YJ201544)。
文摘SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment,the supports were then used to load the active phase Cr Oxthrough a conventional impregnation method.The resulting catalysts were characterized by small/wide angle XRD,N_(2) adsorption/desorption,FT-IR,TEM-EDX,XPS,TPR and CO_(2)-TPD to study the feature of structure,surface chemical state,redox and basicity.It was found from these results that the metal species could be well dispersed on catalysts with larger pore size.Cr^(6+)species could enter into the framework by substituting the Si atoms of SBA-15,and Cr^(3+)mainly exist on extra framework.Pore size had profound effects on reducibility,surface composition and basicity.Cr^(6+)species were necessary to activate the C-H bonds of alkanes,while the basicity played an important role in activating C-O bonds of CO_(2).The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO_(2).
基金supported by the National High Technology Research and Development Program of China(863 Program)(2012AA053305)the International Cooperation Project from Ministry of Science and Technology of China(2010DFA64080)
文摘In this work, the morphologies and pore structures of a series of corncob-derived activated carbons and zeolite templated carbon with ultrahigh surface area were carefully investigated by SEM, HRTEM and N2-sorption characterization technologies. The high-pressure hydrogen uptake performance was analyzed using standard Pressure-Composition-Temperature apparatus in order to study the pore size effects on hydrogen uptake. These as-obtained porous carbons showed different characteristics of pore size distribution as well as specific surface area. The results indicate that the most effective pores for adsorbing hydrogen depended on the storage pressure. These ultramicropores （0.65-0.85 nm） could be the most effective pores on excess H2 uptake at 1 bar, however, micropores （0.85-2 nm） would play a more important role in excess H2 uptake at higher pressure at 77 K. At room temperature, pore size effects on H2 uptake capacity were very weak. Both specific surface area and total pore volume play more important roles than pore size for H2 uptake at room temperature, which was clearly different from that at 77 K. For applications in future, the corncob-derived activated carbons can be more available than zeolite templated carbons at 77 K. Element doping enhanced hydrogen uptake could be main research direction for improving H2 uptake capacity at room temperature.
文摘A novel negative thermal expansion(NTE) material NdMnO_(3) was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO_(3) were investigated by variable temperature X-ray diffraction(XRD), scanning electron microscope(SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O' phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO_(3) shows negative thermal expansion of-4.7×10^(-6)/K. As temperature increases, the ceramic NdMnO_(3) presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is-18.88×10^(-6)/K. The physical mechanism of NTE is discussed and clarified through experiments.
基金the Project of National Natural Science Foundation of China(21822809&21978256)the National Science Fund for Distinguished Young(21525627)+1 种基金the Fundamental Research Funds for the Central Universi-ties(2019XZZX004-03)Ningxia Collaborative Innovation Center for Value Upgrading of Coal-based Synthetic Resin(2017DC57)are gratefully acknowledged.Dr.Zuwei Liao express their dedication to Prof.Xingtian Shu on the occasion of his 80th birthday.
文摘Coke is an important medium for connecting reaction and regeneration of the methanol to propylene process on the ZSM5 catalyst.Coke grows in the meso and macro pores,it gradually worsens the diffusion inside the catalyst particle.Furthermore,pore plugging is inevitable which causes the deactivation of ZSM5 catalyst.However,current continuum model cannot reflect the changes in pore structure with clear physical concepts.A discrete model that is verified by the carbon deposition experiments is introduced to indicate the behavior of pore plugging effects.Results show that the pore plugging has a significant effect on the performance of the catalyst.The time varying profile of effectiveness factor is obtained,indicating a regular reduction with the increase of the pore plugging effect.Spatial distributions of pore size that would significantly enhance the plugging effect are also identified.
基金the financial support from the National Natural Science Foundation of China (No. 51274230)the Natural Science Foundation of Shandong Province (No. ZR2012EEL01)the Fundamental Research Funds for the Central Universities (No. 14CX02040A and No. 14CX06023A)
文摘A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential method.All types of pores are simultaneously introduced to the composite during the differential iteration process according to the ratio of their volume fractions.Based on this model,the effects of pore structures on predicted pore-pressure in carbonates were analyzed.Calculation results indicate that cracks with low pore aspect ratios lead to pore-pressure overestimation which results in lost circulation and reservoir damage.However,moldic pores and vugs with high pore aspect ratios lead to pore-pressure underestimation which results in well kick and even blowout.The pore-pressure deviation due to cracks and moldic pores increases with an increase in porosity.For carbonates with complex pore structures,adopting conventional pore-pressure prediction methods and casing program designs will expose the well drilling engineering to high uncertainties.Velocity prediction models considering the influence of pore structure need to be built to improve the reliability and accuracy of pore-pressure prediction in carbonates.
基金Supported by China National Science and Technology Major Project(2016ZX05025-003-010) and (2016ZX05010-005).
文摘To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil recovery of SP flooding was investigated at the pore, core and field scales through conducting experiments on natural core samples with three typical types of pore structures. First, the in-situ nuclear magnetic resonance core flooding test was carried out to capture the remaining oil variation features in the water flooding and SP flooding through these three types of cores. Subsequently, at the core scale, displacement characteristics and performances of water flooding and SP flooding in these three types of cores were evaluated based on the full-size core flooding tests. Finally, at the field scale, production characteristics of SP flooding in the bimodal sandstone reservoir and multimodal conglomerate reservoir were compared using the actual field production data. The results show: as the pore structure gets more and more complex, the water flooding performance gets poorer, but the incremental recovery factor by SP flooding gets higher;the SP flooding can enhance the producing degree of oil in 1-3 μm pores in the unimodal and bimodal core samples, while it produces largely oil in medium and large pores more than 3 μm in pore radius in the multimodal core sample. The core flooding test using full-size core sample demonstrates that the injection of SP solution can significantly raise up the displacement pressure of the multimodal core sample, and greatly enhance recovery factor by emulsifying the remaining oil and enlarging swept volume. Compared with the sandstone reservoir, the multimodal conglomerate reservoir is more prone to channeling. With proper profile control treatments to efficiently enlarge the microscopic and macroscopic swept volumes, SP flooding in the conglomerate reservoir can contribute to lower water cuts and longer effective durations.
基金supported by the National Natural Science Foundation of China(No.U19B6003)。
文摘The connectivity of shale pores and the occurrence of movable oil in shales have long been the focus of research.In this study,samples from wells BX7 and BYY2 in the Eq3^4-10 cyclothem of Qianjiang Formation in the Qianjiang depression,were analyzed.A double mercury injection method was used to distinguish between invalid and effective connected pores.The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were identified by comparing pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections.The results show that less than 50%of the total connected pores in the Eq34-10 cyclothem samples are effective.The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies.The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15 nm.In Well BYY2,residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10-200 nm,and in bulk argillaceous dolomite facies,it was mainly concentrated at 60-300 nm.The throats of hydrocarbon-retaining pores can be 5 nm or even smaller,but pores with movable shale oil in the well were found to have throat sizes greater than 40 nm.Excluding the influence of differences in wettability,the movability of shale oil is mainly affected by differences in lithofacies,the degree of pore deformation caused by diagenesis,the complexity of pore structures,and the connectivity of pore throats.Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.
基金supported by the National Natural Science Foundation of China“Research on nanopore structure characterization and seepage mechanism of shale reservoirs”(No.:51674044)Chongqing Key Industry Common Key Technology Innovation Special Project“Exploration and development key technology and its application of shale gas in Chongqing”(No.:cstc2017zdcyzdyfx0040)+1 种基金Sichuan Applied Basic Research Project“Research on intelligent evaluation system of marine shale gas construction and production core area(provincial key project)”(No.:2019YJ0340)Sichuan Promising Key Project“Study on evaluation of the fracturing effect of shale gas reservoirs based on the law of fracturing fluid flow back”(No.:2019JDRC0095).
文摘The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas reservoirs,do not take the unconnected pores into account,which impacts the evaluation accuracy of reservoir pore effectiveness.To solve this problem,this paper took the shale of Lower Silurian Longmaxi Formation in the southern Sichuan Basin as the research object to carry out experiments on core porosity,centrifugal+gradual drying NMR after saturated with brine and NMR freezeethaw using plunger samples and crushed samples to analyze the volume,main development location and main pore size distribution range of unconnected pores.Then,the pore systems were classified,and the lower limit of effective pore size of connected gas-bearing pores was determined.Finally,the total pore effectiveness of shale gas reservoirs was evaluated,and the influence of unconnected pores on the development of shale gas was discussed.And the following research results were obtained.First,there are a large number of unconnected pores in the shale gas reservoirs of the study area,accounting for 30.23%.Most of them are mainly developed in organic matters and a few are developed in clay minerals.The distribution of pore size ranges from 5 nm to 30 nm.Second,T_(2)cut-off value of clay bound water in the shale gas reservoirs of the study area is 0.26 ms,whose corresponding pore size is 5.35 nm,which is the lower limit of the effective pore size.Third,large-scale hydraulic fracturing can improve the unconnected pores with the size more than 5.35 nm,so effective development of shale gas will be realized.Fourth,after hydraulic fracturing stimulation,the unconnected pores can increase the storage space of fracturing fluid in the matrix,absorb the fracturing fluid in the fractures,replace the shale gas in the pores and promote the automatic alleviation of water lock in shale gas reservoirs,so the single-well shale gas production will be increased.In conclusion,fluid occurrence and pore system in shale pores can be quantitatively divided by means of centrifugal+gradual temperature drying method combined with NMR experiments,mobile water and capillary bound water can be determined by the high speed centrifugal+NMR experiments,and capillary bound water and clay bound water can be determined by the gradual drying t NMR experiments.
文摘Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for both the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are both the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure.
基金Financial supports for this work provided by the National Basic Research Program of China(2013CB227900)the Innovation of Graduate Student Training Project in Jiangsu Province of China(CXZZ13_0934)
文摘In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture and pore structure features of the strata, and identified the main channels which govern the permeability and water-resisting ability of the strata. The permeability of the upper, central and lower strata shows as 2.0504 × 10^-3-2.782762× 10^-3, 4.1092 × 10^-3 -7.3387 × 10^-3 and 2.0891 ×10^-3-3.2705 × 10-3 μm^2, respectively, and porosity of that is 0.6786-0.9197%, 0.3109-0.3951% and 0.9829-1.8655%, respectively. The results indicate that： （I） the main channels of the relative water-resisting layer are the pore throats with a diameter more than 6 μm; （2） the major proportion of pore throats in the vertical flow channel and the permeability first increases and then sharply decreases; （3） the fractures occurring from the top to 20 m in depth of the strata were filled and there occurred almost no fracture under the depth of 40 m; and （4） the ratio of turning point of the main flow channel in the strata on top of Ordovician can be used to confirm the thickness of filled water-resisting lavers.
基金funding by the German Federal Ministry of Economics and Technology (BMWi) under contract No.02E10377the French National Radioactive Waste Management Agency (Andra)
文摘Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:(1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation,(2) hydraulic drained and undrained boundaries, and(3) heating from ambient temperature up to 90℃-120℃ and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50801005)
文摘It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method （FEM） and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.
基金supported by the Yalongjiang River Joint Fund by the National Natural Science Foundation of China(NSFC)Ertan Hydropower Development Company,LTD(Nos.50579091 and 50539090)+1 种基金NSFC(No.10772190)Major State Basic Research Project of China(No.2002CB412708)
文摘Physical mechanisms and influencing factors on the effective stress coefficient for rock/soil-like porous materials are investigated, based on which equivalent connectivity index is proposed. The equivalent connectivity index, relying on the meso-scale structure of porous material and the property of liquid, denotes the connectivity of pores in Representative Element Area （REA）. If the conductivity of the porous material is anisotropic, the equivalent connectivity index is a second order tensor. Based on the basic theories of continuous mechanics and tensor analysis, relationship between area porosity and volumetric porosity of porous materials is deduced. Then a generalized expression, describing the relation between effective stress coefficient tensor and equivalent connectivity tensor of pores, is proposed, and the expression can be applied to isotropic media and also to anisotropic materials. Furthermore, evolution of porosity and equivalent connectivity index of the pore are studied in the strain space, and the method to determine the corresponding functions in expressions above is proposed using genetic algorithm and genetic programming. Two applications show that the results obtained by the method in this paper perfectly agree with the test data. This paper provides an important theoretical support to the coupled hydro-mechanical research.
