To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflect...To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data.The multibeam bathymetry data show East-North-East(ENE)ridges,piggy-back basins,canyon and channel systems,and the morphology of the abyssal plain.Continuous and discontinuous bottom simulating reflectors(BSRs)occur in the piggy-back basins on most of the seismic profiles available.The BSRs cut the dipping layers with strong amplitude and reversed polarity.Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and sugge st alternating sediments of fine and relatively coarse grain size.Double BSRs are highly dynamic and attributed to slumps occurring in the study area.The BSRs induced by slumps are located both at deep and shallow depths,responding to the temperature or pressure variation.For the first time,BSRs are observed in the abyssal plain of the Makran area,being associated with anticline structures,which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways,including deep fault,gas chimney,and high-permeable sedimentary layer.Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas.Moreover,results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.展开更多
Using the collected 433 heat flow values, we estimated the bases of methane hydrate stability zone （BHSZ）, in northern South China Sea （NSCS）. Through comparing BHSZs with the depths of bottom simulating reflecto...Using the collected 433 heat flow values, we estimated the bases of methane hydrate stability zone （BHSZ）, in northern South China Sea （NSCS）. Through comparing BHSZs with the depths of bottom simulating reflectors （BSRs）, in Shenhu Area （SA）, we found that there are big differences between them. In the north of SA, where the water depth is shallow, many slumps developed and the sedimentation rate is high, it appears great negative difference （as large as -192%）. However, to the southeast of SA, where the water depth is deeper, sedimentation rate is relatively low and uplift basement topography exists, it changes to positive difference （as large as ＋45%）. The differences change so great, which haven＇t been observed in other places of the world. After considering the errors from the process of heat flow measurement, the BSR depth, the relationship of thermal conductivity with the sediments depth, and the fluid flow activities, we conclude that the difference should be not caused by these errors. Such big disagreement may be due to the misunderstanding of BSR. The deviant ＂BSRs＂ could represent the paleo-BSRs or just gas-bearing sediment layers, such as unconformities or the specific strata where have different permeability, which are not hydraterelated BSRs.展开更多
Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These ...Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These bodies are divided into seven types on the basis of theirshapes,intermal structures and geneses(slide,collapse and deformation above BSRs,as well asthe slump wedge,lens,block and sheet below BSRs).Based on this classification,detailed studieswere conducted,including measurements of the slump body sizes and slope gradients of landslides,depiction of their three-dimensional characteristics,and research on the landslide distribution.Todetermine the genetic differences of these seven types,this study analyses the possibility of verticalflow-pattern-transformation and mechanisms of submarine landsltide formation.Results show that thedominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted fromgas hydrate decomposition,with possible fransformation between flow patterns.Finally,there are twokinds of relationships between submarine landslides and BSRs since the free gas either influences thesubmarine landslide bodies below or above BSRs,resulting in two types of submarine landslide bodyassociations:Type A is characterized by submarine slide above BSRs and slump lens below BSRs,whereas Type B shows deformation above BSRs and slump blocks below BSRs.Type Ais favourablefor gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.展开更多
认清地质历史时期相关的流体运移和海底甲烷渗漏是天然气水合物研究中的重要问题,对了解水合物成藏、评价水合物分解过程中甲烷渗漏可能造成的环境影响有重要指导作用。本文通过对全球海域大量天然气水合物发育区进行再解释,分析流体运...认清地质历史时期相关的流体运移和海底甲烷渗漏是天然气水合物研究中的重要问题,对了解水合物成藏、评价水合物分解过程中甲烷渗漏可能造成的环境影响有重要指导作用。本文通过对全球海域大量天然气水合物发育区进行再解释,分析流体运移通道、海底甲烷渗漏与天然气水合物系统三者间的关系。首先,按照流体运移通道在水合物系统中的作用将其分为两类:类型Ⅰ主要分布在水合物稳定区底界(BSR)之下,为水合物系统成藏提供气源的通道,类型Ⅱ分布在BSR以浅,甚至延伸至海底,为水合物系统中的甲烷逃逸提供渗漏通道。另外,分析认为多边形断层作为通道疏导油气垂向运移的作用是有限的。其次,根据海底甲烷渗漏与天然气水合物系统的位置关系以及渗漏的甲烷气源条件,将海底甲烷渗漏特征分为三大类五小类:水合物稳定边界以深(水合物系统气源、非水合物系统气源)、水合物稳定边界附近(水合物系统气源、非水合物系统气源)和水合物稳定边界以浅(非水合物系统气源)。其中,水合物稳定区向陆分布边界LLGHSZ(landward limit of gas hydrate stability zone)附近的甲烷渗漏强度和密度最大。综上,本文提出的流体运移通道与海底甲烷渗漏特征的分类方法对认识动态天然气水合物系统的成藏和分解过程、评价相关的环境和气候影响具有一定的指导作用。展开更多
The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms...The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms of free gas remains limited.This study identifies structural elements associated with free gas,such as thrust faults,piggyback basins,unconformities,and décollements,through detailed interpretation of newly acquired seismic data.Free gas reservoirs within piggyback basins are located in the folded zone of the accretionary prism,whereas unconformity-type and horizontal sandstone-type free gas reservoirs are identified in undeformed areas.In the folded zone,décollement,thrust faults,and permeable sand layers act as primary migration pathways for free gas,which accumulates in turbidite sands beneath bottom simulating reflectors(BSRs)in piggyback basins.In the undeformed zone,free gas migrates along décollements and thrust faults into horizontal sandstones,where substantial accumulations are found near unconformities below BSRs.The distribution of free gas reservoirs across the study area is extensive and diverse.This study is the first to document unconformity-type and horizontal sandstone-type free gas reservoirs in the undeformed zone,highlighting their considerable resource potential.The findings are of substantial value for oil and gas exploration at the front of the accretionary prism and provide important theoretical and practical insights into natural gas accumulation systems along active continental margins.展开更多
基金the Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology(No.MMRKF201810)the China Geological Survey(Nos.DD20190582,DD20191009,DD20160214)funded by the Shandong Province"Taishan Scholar"Construction Project。
文摘To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data.The multibeam bathymetry data show East-North-East(ENE)ridges,piggy-back basins,canyon and channel systems,and the morphology of the abyssal plain.Continuous and discontinuous bottom simulating reflectors(BSRs)occur in the piggy-back basins on most of the seismic profiles available.The BSRs cut the dipping layers with strong amplitude and reversed polarity.Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and sugge st alternating sediments of fine and relatively coarse grain size.Double BSRs are highly dynamic and attributed to slumps occurring in the study area.The BSRs induced by slumps are located both at deep and shallow depths,responding to the temperature or pressure variation.For the first time,BSRs are observed in the abyssal plain of the Makran area,being associated with anticline structures,which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways,including deep fault,gas chimney,and high-permeable sedimentary layer.Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas.Moreover,results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.
基金The National Natural Science Foundation of China under contract No. 40774033863 Program under contract No. 2006AA09A203-05973 Program under contract No. 2009CB219503
文摘Using the collected 433 heat flow values, we estimated the bases of methane hydrate stability zone （BHSZ）, in northern South China Sea （NSCS）. Through comparing BHSZs with the depths of bottom simulating reflectors （BSRs）, in Shenhu Area （SA）, we found that there are big differences between them. In the north of SA, where the water depth is shallow, many slumps developed and the sedimentation rate is high, it appears great negative difference （as large as -192%）. However, to the southeast of SA, where the water depth is deeper, sedimentation rate is relatively low and uplift basement topography exists, it changes to positive difference （as large as ＋45%）. The differences change so great, which haven＇t been observed in other places of the world. After considering the errors from the process of heat flow measurement, the BSR depth, the relationship of thermal conductivity with the sediments depth, and the fluid flow activities, we conclude that the difference should be not caused by these errors. Such big disagreement may be due to the misunderstanding of BSR. The deviant ＂BSRs＂ could represent the paleo-BSRs or just gas-bearing sediment layers, such as unconformities or the specific strata where have different permeability, which are not hydraterelated BSRs.
文摘Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These bodies are divided into seven types on the basis of theirshapes,intermal structures and geneses(slide,collapse and deformation above BSRs,as well asthe slump wedge,lens,block and sheet below BSRs).Based on this classification,detailed studieswere conducted,including measurements of the slump body sizes and slope gradients of landslides,depiction of their three-dimensional characteristics,and research on the landslide distribution.Todetermine the genetic differences of these seven types,this study analyses the possibility of verticalflow-pattern-transformation and mechanisms of submarine landsltide formation.Results show that thedominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted fromgas hydrate decomposition,with possible fransformation between flow patterns.Finally,there are twokinds of relationships between submarine landslides and BSRs since the free gas either influences thesubmarine landslide bodies below or above BSRs,resulting in two types of submarine landslide bodyassociations:Type A is characterized by submarine slide above BSRs and slump lens below BSRs,whereas Type B shows deformation above BSRs and slump blocks below BSRs.Type Ais favourablefor gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.
文摘认清地质历史时期相关的流体运移和海底甲烷渗漏是天然气水合物研究中的重要问题,对了解水合物成藏、评价水合物分解过程中甲烷渗漏可能造成的环境影响有重要指导作用。本文通过对全球海域大量天然气水合物发育区进行再解释,分析流体运移通道、海底甲烷渗漏与天然气水合物系统三者间的关系。首先,按照流体运移通道在水合物系统中的作用将其分为两类:类型Ⅰ主要分布在水合物稳定区底界(BSR)之下,为水合物系统成藏提供气源的通道,类型Ⅱ分布在BSR以浅,甚至延伸至海底,为水合物系统中的甲烷逃逸提供渗漏通道。另外,分析认为多边形断层作为通道疏导油气垂向运移的作用是有限的。其次,根据海底甲烷渗漏与天然气水合物系统的位置关系以及渗漏的甲烷气源条件,将海底甲烷渗漏特征分为三大类五小类:水合物稳定边界以深(水合物系统气源、非水合物系统气源)、水合物稳定边界附近(水合物系统气源、非水合物系统气源)和水合物稳定边界以浅(非水合物系统气源)。其中,水合物稳定区向陆分布边界LLGHSZ(landward limit of gas hydrate stability zone)附近的甲烷渗漏强度和密度最大。综上,本文提出的流体运移通道与海底甲烷渗漏特征的分类方法对认识动态天然气水合物系统的成藏和分解过程、评价相关的环境和气候影响具有一定的指导作用。
基金the National Natural Science Foundation of China(Nos.42076069,41406080)the Laoshan Laboratory Science and Technology Innovation Project(No.LSKJ202203401)the China Geological Survey Project(Nos.DD20190581,DD20160155)。
文摘The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms of free gas remains limited.This study identifies structural elements associated with free gas,such as thrust faults,piggyback basins,unconformities,and décollements,through detailed interpretation of newly acquired seismic data.Free gas reservoirs within piggyback basins are located in the folded zone of the accretionary prism,whereas unconformity-type and horizontal sandstone-type free gas reservoirs are identified in undeformed areas.In the folded zone,décollement,thrust faults,and permeable sand layers act as primary migration pathways for free gas,which accumulates in turbidite sands beneath bottom simulating reflectors(BSRs)in piggyback basins.In the undeformed zone,free gas migrates along décollements and thrust faults into horizontal sandstones,where substantial accumulations are found near unconformities below BSRs.The distribution of free gas reservoirs across the study area is extensive and diverse.This study is the first to document unconformity-type and horizontal sandstone-type free gas reservoirs in the undeformed zone,highlighting their considerable resource potential.The findings are of substantial value for oil and gas exploration at the front of the accretionary prism and provide important theoretical and practical insights into natural gas accumulation systems along active continental margins.
