The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the d...The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.展开更多
It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because o...It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.展开更多
天然气水合物是重要的非常规能源,通过室内模拟实验模拟水合物赋存环境条件,观察水合物在沉积物中的合成/分解过程及其物性演化规律是揭示实际天然气水合物成藏/分解规律的重要途径。天然气水合物成藏过程中沉积物体系内部变化过程的可...天然气水合物是重要的非常规能源,通过室内模拟实验模拟水合物赋存环境条件,观察水合物在沉积物中的合成/分解过程及其物性演化规律是揭示实际天然气水合物成藏/分解规律的重要途径。天然气水合物成藏过程中沉积物体系内部变化过程的可视化在线监测已成为天然气水合物室内模拟的重要发展方向之一(Wu Nengyou et al.,2018)。目前已经发展的X-CT成像、Raman成像、电子显微成像、核磁共振成像等技术手段为孔隙尺度的天然气水合物成藏/分解机理研究提供了基础,但大岩芯尺度(~cm)或中试尺度(~m)的水合物系统成像观测技术仍有待进一步完善。展开更多
基金supported by the Qingdao Natural Science Foundation(No.23-2-1-54-zyyd-jch)the National Natural Science Foundation of China(Nos.42076217,41976074)+1 种基金the Laoshan Laboratory(No.LSKJ202203506)the Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University(No.KLE-TJGE-G2202).
文摘The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.
基金financially supported by the Natural Science Foundation of Shandong Province(No.ZR202011030013)the National Natural Science Foundation of China(No.41976205)+1 种基金the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2021QNLM020002)the China Geological Survey Program(No.DD20221704).
文摘It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.
文摘天然气水合物是重要的非常规能源,通过室内模拟实验模拟水合物赋存环境条件,观察水合物在沉积物中的合成/分解过程及其物性演化规律是揭示实际天然气水合物成藏/分解规律的重要途径。天然气水合物成藏过程中沉积物体系内部变化过程的可视化在线监测已成为天然气水合物室内模拟的重要发展方向之一(Wu Nengyou et al.,2018)。目前已经发展的X-CT成像、Raman成像、电子显微成像、核磁共振成像等技术手段为孔隙尺度的天然气水合物成藏/分解机理研究提供了基础,但大岩芯尺度(~cm)或中试尺度(~m)的水合物系统成像观测技术仍有待进一步完善。
