Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coa...Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.展开更多
To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method opt...To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method optimizes drilling media tailored to specific coal seams and fine-tunes technical parameters during drilling and permeability improvement processes.Furthermore,it clarifies the relationships among the coal breaking rate,discharge of drill cuttings,jet velocity,rotation speed,and displacement.This ensures precise and effective permeability improvement in both soft and hard coal formations.To implement this technology,a set of high-performance drilling tool with a large inner diameter,high pressure resistance,and superior sealing capabilities has been developed.Consisting of a water braid,drill pipe and hydraulic ejector,this tool meets the requirements of substantial displacement and high pump pressure.Field test results demonstrate remarkable enhancements in borehole formation,coal breaking and slagging efficiency.Specifically,the operation time is reduced by 60%–80%,the coal output is increased by 1–1.5 times,the pure coal seam gas extraction yield is increased by 1–2 times,and the extraction radius expands by more than 100%.These results highlight significant advancements in operational efficiency and permeability improvement effects,paving the way for efficient and economical coal seam gas extraction practices.展开更多
Fines migration induced by injection of low-salinity water(LSW) into porous media can lead to severe pore plugging and consequent permeability reduction. The deepbed filtration(DBF) theory is used to model the aforeme...Fines migration induced by injection of low-salinity water(LSW) into porous media can lead to severe pore plugging and consequent permeability reduction. The deepbed filtration(DBF) theory is used to model the aforementioned phenomenon, which allows us to predict the effluent concentration history and the distribution profile of entrapped particles. However, the previous models fail to consider the movement of the waterflood front. In this study, we derive a stochastic model for fines migration during LSW flooding, in which the Rankine-Hugoniot condition is used to calculate the concentration of detached particles behind and ahead of the moving water front. A downscaling procedure is developed to determine the evolution of pore-size distribution from the exact solution of a large-scale equation system. To validate the proposed model,the obtained exact solutions are used to treat the laboratory data of LSW flooding in artificial soil-packed columns. The tuning results show that the proposed model yields a considerably higher value of the coefficient of determination, compared with the previous models, indicating that the new model can successfully capture the effect of the moving water front on fines migration and precisely match the effluent history of the detached particles.展开更多
Structure of porous media and fluid distribution in rocks can significantly affect the transport characteristics during the process of microscale tracer flow.To clarify the effect of micro heterogeneity on aqueous tra...Structure of porous media and fluid distribution in rocks can significantly affect the transport characteristics during the process of microscale tracer flow.To clarify the effect of micro heterogeneity on aqueous tracer transport,this paper demonstrates microscopic experiments at pore level and proposes an improved mathematical model for tracer transport.The visualization results show a faster tracer movement into movable water than it into bound water,and quicker occupancy in flowing pores than in storage pores caused by the difference of tracer velocity.Moreover,the proposed mathematical model includes the effects of bound water and flowing porosity by applying interstitial flow velocity expression.The new model also distinguishes flowing and storage pores,accounting for different tracer transport mechanisms(dispersion,diffusion and adsorption)in different types of pores.The resulting analytical solution better matches with tracer production data than the standard model.The residual sum of squares(RSS)from the new model is 0.0005,which is 100 times smaller than the RSS from the standard model.The sensitivity analysis indicates that the dispersion coefficient and flowing porosity shows a negative correlation with the tracer breakthrough time and the increasing slope,whereas the superficial velocity and bound water saturation show a positive correlation.展开更多
Underground constructions often encounter water environments,where water–rock interaction can increase porosity,thereby weakening engineering rocks.Correspondingly,the failure criterion for chemically corroded rocks ...Underground constructions often encounter water environments,where water–rock interaction can increase porosity,thereby weakening engineering rocks.Correspondingly,the failure criterion for chemically corroded rocks becomes essential in the stability analysis and design of such structures.This study enhances the applicability of the Hoek-Brown(H-B)criterion for engineering structures operating in chemically corrosive conditions by introducing a kinetic porosity-dependent instantaneous mi(KPIM).A multiscale experimental investigation,including nuclear magnetic resonance(NMR),X-ray diffraction(XRD),scanning electron microscopy(SEM),pH and ion chromatography analysis,and triaxial compression tests,is employed to quantify pore structural changes and their linkage with the strength responses of limestone under coupled chemical-mechanical(C-M)conditions.By employing ion chromatography and NMR analysis,along with incorporating the principles of free-face dissolution theory accounting for both congruent and incongruent dissolution,a kinetic chemical corrosion model is developed.This model aims to calculate the kinetic porosity alterations within rocks exposed to varying H+concentrations and durations.Subsequently,utilizing the generalized mixture rule(GMR),the kinetic porositydependent mi is formulated.Evaluation of the KPIM-enhanced H-B criterion using compression test data from 5 types of rocks demonstrated a high level of consistency between the criterion and the experimental results,with a coefficient of determination greater than 0.96,a mean absolute percentage error less than 4.84%,and a root-mean-square deviation less than 5.95 MPa.Finally,the physical significance of the porosity-dependent instantaneous mi is clarified:it serves as an indicator of a rock’s capacity to leverage the confining pressure effect.展开更多
基金supported by the National Natural Science Foundation of China(42072193,42230804,Xianbo Su)the National Overseas Top Talents Program of China(JXRSB02001,Zhenjiang You).
文摘Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.
基金supported by the National Natural Science Foundation of China(42230804,42072193,Xianbo Su)the National Overseas Top Talents Program of China(JXRSB02001,Zhenjiang You).
文摘To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method optimizes drilling media tailored to specific coal seams and fine-tunes technical parameters during drilling and permeability improvement processes.Furthermore,it clarifies the relationships among the coal breaking rate,discharge of drill cuttings,jet velocity,rotation speed,and displacement.This ensures precise and effective permeability improvement in both soft and hard coal formations.To implement this technology,a set of high-performance drilling tool with a large inner diameter,high pressure resistance,and superior sealing capabilities has been developed.Consisting of a water braid,drill pipe and hydraulic ejector,this tool meets the requirements of substantial displacement and high pump pressure.Field test results demonstrate remarkable enhancements in borehole formation,coal breaking and slagging efficiency.Specifically,the operation time is reduced by 60%–80%,the coal output is increased by 1–1.5 times,the pure coal seam gas extraction yield is increased by 1–2 times,and the extraction radius expands by more than 100%.These results highlight significant advancements in operational efficiency and permeability improvement effects,paving the way for efficient and economical coal seam gas extraction practices.
基金the National Natural Science Foundation of China(Nos.51804316,51734010,and U1762211)the National Science and Technology Major Project of China(No.2017ZX05009)the Science Foundation of China University of Petroleum,Beijing(No.2462017YJRC037)。
文摘Fines migration induced by injection of low-salinity water(LSW) into porous media can lead to severe pore plugging and consequent permeability reduction. The deepbed filtration(DBF) theory is used to model the aforementioned phenomenon, which allows us to predict the effluent concentration history and the distribution profile of entrapped particles. However, the previous models fail to consider the movement of the waterflood front. In this study, we derive a stochastic model for fines migration during LSW flooding, in which the Rankine-Hugoniot condition is used to calculate the concentration of detached particles behind and ahead of the moving water front. A downscaling procedure is developed to determine the evolution of pore-size distribution from the exact solution of a large-scale equation system. To validate the proposed model,the obtained exact solutions are used to treat the laboratory data of LSW flooding in artificial soil-packed columns. The tuning results show that the proposed model yields a considerably higher value of the coefficient of determination, compared with the previous models, indicating that the new model can successfully capture the effect of the moving water front on fines migration and precisely match the effluent history of the detached particles.
基金funded by National Science and Technology Major Projects(2017ZX05009004,2016ZX05058003)Beijing Natural Science Foundation(2173061)and State Energy Center for Shale Oil Research and Development(G5800-16-ZS-KFNY005).
文摘Structure of porous media and fluid distribution in rocks can significantly affect the transport characteristics during the process of microscale tracer flow.To clarify the effect of micro heterogeneity on aqueous tracer transport,this paper demonstrates microscopic experiments at pore level and proposes an improved mathematical model for tracer transport.The visualization results show a faster tracer movement into movable water than it into bound water,and quicker occupancy in flowing pores than in storage pores caused by the difference of tracer velocity.Moreover,the proposed mathematical model includes the effects of bound water and flowing porosity by applying interstitial flow velocity expression.The new model also distinguishes flowing and storage pores,accounting for different tracer transport mechanisms(dispersion,diffusion and adsorption)in different types of pores.The resulting analytical solution better matches with tracer production data than the standard model.The residual sum of squares(RSS)from the new model is 0.0005,which is 100 times smaller than the RSS from the standard model.The sensitivity analysis indicates that the dispersion coefficient and flowing porosity shows a negative correlation with the tracer breakthrough time and the increasing slope,whereas the superficial velocity and bound water saturation show a positive correlation.
文摘Underground constructions often encounter water environments,where water–rock interaction can increase porosity,thereby weakening engineering rocks.Correspondingly,the failure criterion for chemically corroded rocks becomes essential in the stability analysis and design of such structures.This study enhances the applicability of the Hoek-Brown(H-B)criterion for engineering structures operating in chemically corrosive conditions by introducing a kinetic porosity-dependent instantaneous mi(KPIM).A multiscale experimental investigation,including nuclear magnetic resonance(NMR),X-ray diffraction(XRD),scanning electron microscopy(SEM),pH and ion chromatography analysis,and triaxial compression tests,is employed to quantify pore structural changes and their linkage with the strength responses of limestone under coupled chemical-mechanical(C-M)conditions.By employing ion chromatography and NMR analysis,along with incorporating the principles of free-face dissolution theory accounting for both congruent and incongruent dissolution,a kinetic chemical corrosion model is developed.This model aims to calculate the kinetic porosity alterations within rocks exposed to varying H+concentrations and durations.Subsequently,utilizing the generalized mixture rule(GMR),the kinetic porositydependent mi is formulated.Evaluation of the KPIM-enhanced H-B criterion using compression test data from 5 types of rocks demonstrated a high level of consistency between the criterion and the experimental results,with a coefficient of determination greater than 0.96,a mean absolute percentage error less than 4.84%,and a root-mean-square deviation less than 5.95 MPa.Finally,the physical significance of the porosity-dependent instantaneous mi is clarified:it serves as an indicator of a rock’s capacity to leverage the confining pressure effect.
