Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused o...Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused on shale matrix,and the pressure conditions discussed were mostly atmospheric.The initial imbibition behavior begins from propped fractures to matrix,but there are few studies working on explaining the imbibition behavior in propped fractures or the phenomenon of many shale wells exhibit higher productivity after a“soaking”period.Therefore,propped fracture samples were designed for imbibition and migration experiments.In order to accurately study the mechanism and main influencing factors of fracturing fluid imbibition and migration in propped and unpropped shale fractures under high temperature and high pressure,a series of experiments based on nuclear magnetic resonance(NMR)were carried out.Results showed that NMR T_(2) spectra of all samples exhibited a bimodal distribution.The final imbibition volume of fracturing fluid was positively related to pressure and fracture width.The imbibition effect of fracturing fluid was more evident in matrix pores under high pressure.In the migration during soaking stage,the fracturing fluid gradually migrated from large pores to small pores and gradually displaced the shale gas from the matrix,thus allowing the water blocking in propped fractures to self-unlock to some extent.Gas permeability decreased in the imbibition stage,while it recovered in the migration stage to some extent.展开更多
This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the...This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the expandable device could have much higher strength(>89 MPa)by laboratory tests,and the load bearing capacity of the expandable prop may depend on the stability of the supporting steel pipe structure.A good agreement was found between the laboratory test and numerical results in terms of the load bearing capacity and the final macro-bending failure pattern for expandable props with heights of 1.5 and 2.7 m,and the theoretical calculation for the strength of traditional steel structures is not directly suitable for the expandable props.Moreover,additional numerical simulations were performed for the expandable props with different normalized slenderness ratiosλ_(n)and loading eccentric distances e.The variation of stability coefficient of the expandable prop is in line with the Perry-Robertson equation and its correlation coefficients are fitted as a of 0.979 and b of 0.314.For estimating the load bearing capacity of the expandable props,the strength equation for traditional steel structures is improved by introducing a bending magnification factor and by modifying the normalized slenderness ratio to a converted slenderness ratio.Based on the underground field monitoring for the strength of expandable props with different heights,the empirical eccentric distances were back calculated,and a safety factor is introduced to obtain the designed strength of the expandable prop.In addition,a four-step design procedure is proposed for the expandable prop.展开更多
The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to hig...The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer props. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation,and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input a, β, γ is to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of a, β, γ are discussed. The results show that:(1) In deep high geo-stress roadways, the energyabsorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects.(2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density is the difference among the three. The function of energyabsorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×10^(4) to 1×10^(4)J/m^(3), and amount value from 3.57×10^(8) to 1.90×10^(6)J.(3) When mining is advanced in small steps, the strain energy accumulation is dominated. While in a large step, the released energy is dominant, thus a more dynamic hazards proneness. The energy-absorbing rock bolt and prop can reduce three times strain energy release amount, thus reducing the dynamic hazards. The results suggest that energy-absorbing props and rock bolts can effectively reduce the strain energy in the coal and rock masses, and prevent rock bursts and other hazards.The numerical model developed in this study can also be used to optimize the design of energyabsorbing props and rock bolts for specific mining conditions.展开更多
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China(Grant Nos.52174036,51774243,51904257,51874251)the Sichuan Province Science and Technology Program(Grant Nos.2021YJ0345,2022JDJQ0009,2022NSFSC0186).
文摘Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused on shale matrix,and the pressure conditions discussed were mostly atmospheric.The initial imbibition behavior begins from propped fractures to matrix,but there are few studies working on explaining the imbibition behavior in propped fractures or the phenomenon of many shale wells exhibit higher productivity after a“soaking”period.Therefore,propped fracture samples were designed for imbibition and migration experiments.In order to accurately study the mechanism and main influencing factors of fracturing fluid imbibition and migration in propped and unpropped shale fractures under high temperature and high pressure,a series of experiments based on nuclear magnetic resonance(NMR)were carried out.Results showed that NMR T_(2) spectra of all samples exhibited a bimodal distribution.The final imbibition volume of fracturing fluid was positively related to pressure and fracture width.The imbibition effect of fracturing fluid was more evident in matrix pores under high pressure.In the migration during soaking stage,the fracturing fluid gradually migrated from large pores to small pores and gradually displaced the shale gas from the matrix,thus allowing the water blocking in propped fractures to self-unlock to some extent.Gas permeability decreased in the imbibition stage,while it recovered in the migration stage to some extent.
基金This work was financially supported by the National Key Research and Development Program of China(No.2022YFC2903804)the National Natural Science Foundation of China(Nos.52004054,52274115,51874068 and 52074062).
文摘This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the expandable device could have much higher strength(>89 MPa)by laboratory tests,and the load bearing capacity of the expandable prop may depend on the stability of the supporting steel pipe structure.A good agreement was found between the laboratory test and numerical results in terms of the load bearing capacity and the final macro-bending failure pattern for expandable props with heights of 1.5 and 2.7 m,and the theoretical calculation for the strength of traditional steel structures is not directly suitable for the expandable props.Moreover,additional numerical simulations were performed for the expandable props with different normalized slenderness ratiosλ_(n)and loading eccentric distances e.The variation of stability coefficient of the expandable prop is in line with the Perry-Robertson equation and its correlation coefficients are fitted as a of 0.979 and b of 0.314.For estimating the load bearing capacity of the expandable props,the strength equation for traditional steel structures is improved by introducing a bending magnification factor and by modifying the normalized slenderness ratio to a converted slenderness ratio.Based on the underground field monitoring for the strength of expandable props with different heights,the empirical eccentric distances were back calculated,and a safety factor is introduced to obtain the designed strength of the expandable prop.In addition,a four-step design procedure is proposed for the expandable prop.
基金the National Natural Science Foundation of China(Nos.52204114,52274145,U22A20165,and 52174089)the Natural Science Foundation of Jiangsu Province(No.BK20210522)+2 种基金the National Key Research and Development Program of China(No.2022YFE0128300)the China Postdoctoral Science Foundation(No.2023M733758)the Shandong Postdoctoral Science Foundation(No.SDCX-ZG-202302037).
文摘The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer props. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation,and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input a, β, γ is to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of a, β, γ are discussed. The results show that:(1) In deep high geo-stress roadways, the energyabsorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects.(2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density is the difference among the three. The function of energyabsorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×10^(4) to 1×10^(4)J/m^(3), and amount value from 3.57×10^(8) to 1.90×10^(6)J.(3) When mining is advanced in small steps, the strain energy accumulation is dominated. While in a large step, the released energy is dominant, thus a more dynamic hazards proneness. The energy-absorbing rock bolt and prop can reduce three times strain energy release amount, thus reducing the dynamic hazards. The results suggest that energy-absorbing props and rock bolts can effectively reduce the strain energy in the coal and rock masses, and prevent rock bursts and other hazards.The numerical model developed in this study can also be used to optimize the design of energyabsorbing props and rock bolts for specific mining conditions.
基金Natural Science Foundation of Anhui Province, 2008085QG343, Research on Development and Evolution Mechanism and Policy of Artificial Intelligence Open Innovation Platform。
