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
Pore pressure is an important parameter in coalbed methane(CBM)exploration and development;however,the distribution pattern and mechanism for pore pressure differences in the Upper Permian CBM reservoirs are poorly un...Pore pressure is an important parameter in coalbed methane(CBM)exploration and development;however,the distribution pattern and mechanism for pore pressure differences in the Upper Permian CBM reservoirs are poorly understood in the western Guizhou region of South China.In this study,lateral and vertical variations and mechanisms for pore pressure differences are analyzed based on 126 injection-falloff and in-situ stress well test data measured in Permian coal reservoirs.Generally,based on the pore pressure gradient and coefficient in coal reservoirs of the western Guizhou region,five zones can be delineated laterally:the mining areas of Zhina,northem Liupanshui,northern Guizhou,northwestern Guizhou and southern Liupanshui.Vertically,there are two main typical patterns:i)the pore pressure gradient(or coefficient)is nearly unchanged in different coal reservoirs,and ii)the pore pressure gradient(or coefficient)has cyclic variations in a borehole profile with multiple coal seams,which suggests the existence of a"superimposed CBM system".The mechanism analysis indicates that coal permeability,thermal evolution stage and hydrocarbon generation contribute little to pore pressure differences in coal reservoirs in the western Guizhou region.The present-day in-situ stress field,basement structure and tectonic activity may be the dominant factors affecting lateral pore pressure differences.The sealing capacity of caprocks and the present-day in-situ stress field are significant para-meters causing vertical pore pressure differences in coal reservoirs.These results are expected to provide new geological references for CBM exploration and develop-ment in the western Guizhou region.展开更多
Gas and water migration through the hydrate-bearing sediment are characteristic features in marine gas hydrate reservoirs worldwide.However,there are few experimental investigations on the effect of water-gas flow on ...Gas and water migration through the hydrate-bearing sediment are characteristic features in marine gas hydrate reservoirs worldwide.However,there are few experimental investigations on the effect of water-gas flow on the gas hydrate reservoir.In this study,gas-water migration in gas hydrate stability zone(GHSZ)was investigated visually employing a high-resolution magnetic resonance imaging(MRI)apparatus,and the formation of hydrate seal was experimentally investigated.Results revealed that normal flow of gas-water at the low flow rate of 1–0.25 mL/min will induce the hydrate reformation.Conversely,higher gas-water flow rates(at 2–0.5 and 4–1 mL/min)need higher reservoir pressure to induce the hydrate reformation.In addition,the hydrate reformation during the gas-water flow process produced the hydrate seal,which can withstand an over 9.0 MPa overpressure.This high overpressure provides the development condition for the underlying gas and/or water reservoir.A composite MRI image of the whole hydrate seal was obtained through the MRI.The pore difference between hydrate zone and coexistence zone produces a capillary sealing effect for hydrate seal.The hydrate saturation of hydrate seal was more than 51.6%,and the water saturation was more than 19.3%.However,the hydrate seal can be broken through when the overpressure exceeded the capillary pressure of the hydrate seal,which induced the sudden drop of reservoir pressure.This study provides a scientific explanation for the existence of high-pressure underlying gas below the hydrate layer and is significant for the safe exploitation of these common typical marine hydrate reservoirs.展开更多
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.
基金supported by Natural Science Foundation of Jiangsu Province,China(No.BK20201349)National Natural Science Foundation of China(Grant Nos.41702130 and 41971335)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Pore pressure is an important parameter in coalbed methane(CBM)exploration and development;however,the distribution pattern and mechanism for pore pressure differences in the Upper Permian CBM reservoirs are poorly understood in the western Guizhou region of South China.In this study,lateral and vertical variations and mechanisms for pore pressure differences are analyzed based on 126 injection-falloff and in-situ stress well test data measured in Permian coal reservoirs.Generally,based on the pore pressure gradient and coefficient in coal reservoirs of the western Guizhou region,five zones can be delineated laterally:the mining areas of Zhina,northem Liupanshui,northern Guizhou,northwestern Guizhou and southern Liupanshui.Vertically,there are two main typical patterns:i)the pore pressure gradient(or coefficient)is nearly unchanged in different coal reservoirs,and ii)the pore pressure gradient(or coefficient)has cyclic variations in a borehole profile with multiple coal seams,which suggests the existence of a"superimposed CBM system".The mechanism analysis indicates that coal permeability,thermal evolution stage and hydrocarbon generation contribute little to pore pressure differences in coal reservoirs in the western Guizhou region.The present-day in-situ stress field,basement structure and tectonic activity may be the dominant factors affecting lateral pore pressure differences.The sealing capacity of caprocks and the present-day in-situ stress field are significant para-meters causing vertical pore pressure differences in coal reservoirs.These results are expected to provide new geological references for CBM exploration and develop-ment in the western Guizhou region.
基金supported by the National Key Research and Development Plan of China(2021YFC2800902)the National Natural Science Foundation of China(52206076,U19B2005)+1 种基金the Fundamental Research Funds for the Central Universities of China(DUT21ZD103)the Opening Fund of MOE Key Laboratory of Ocean Energy Utilization and Energy Conservation(LOEC-202204).
文摘Gas and water migration through the hydrate-bearing sediment are characteristic features in marine gas hydrate reservoirs worldwide.However,there are few experimental investigations on the effect of water-gas flow on the gas hydrate reservoir.In this study,gas-water migration in gas hydrate stability zone(GHSZ)was investigated visually employing a high-resolution magnetic resonance imaging(MRI)apparatus,and the formation of hydrate seal was experimentally investigated.Results revealed that normal flow of gas-water at the low flow rate of 1–0.25 mL/min will induce the hydrate reformation.Conversely,higher gas-water flow rates(at 2–0.5 and 4–1 mL/min)need higher reservoir pressure to induce the hydrate reformation.In addition,the hydrate reformation during the gas-water flow process produced the hydrate seal,which can withstand an over 9.0 MPa overpressure.This high overpressure provides the development condition for the underlying gas and/or water reservoir.A composite MRI image of the whole hydrate seal was obtained through the MRI.The pore difference between hydrate zone and coexistence zone produces a capillary sealing effect for hydrate seal.The hydrate saturation of hydrate seal was more than 51.6%,and the water saturation was more than 19.3%.However,the hydrate seal can be broken through when the overpressure exceeded the capillary pressure of the hydrate seal,which induced the sudden drop of reservoir pressure.This study provides a scientific explanation for the existence of high-pressure underlying gas below the hydrate layer and is significant for the safe exploitation of these common typical marine hydrate reservoirs.
