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
BSR （Bottom Simulating Reflector） occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea （SCS）. It is an important seismic reference mark whi...BSR （Bottom Simulating Reflector） occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea （SCS）. It is an important seismic reference mark which identifies the gas hydrate and its distribution influenced by the tectonic movements. Single-point basin modeling was conducted using 473 points in the study area. To discuss the relationships between the tectonic subsidence and BSR, the volume and rate of tectonic subsidence in each geological time have been simulated. The results show that there are three tectonic accelerate subsidence processes in the study area since the late Miocene, especially since 1.8Ma the tectonic subsidence accelerates more apparently. Since the Late Miocene to Pleistocene, the rate of tectonic subsidence in deep-water underwent a transformation from weak to strong. The ratio of tectonic subsidence to the total subsidence was relatively high （65-70%）. Through the superposition of the BSR developed areas and the contours of tectonic subsidence in this area, it was discovered that more than 80% of BSR tend to be distributed at the slope break or depression-uplift structural transfer zone and the average tectonic subsidence rate ranges from 70 m/Ma to 125 m/Ma.展开更多
拟海底反射层(Bottom Simulating Reflector,简称BSR)是水合物底界的地震反射标志,其上部的振幅空白带是含水合物地层的反射特征,下部的高振幅异常区代表了下伏的游离气区(Free Gas Zones,简称FGZs)。利用高分辨率三维地震资料,精细描...拟海底反射层(Bottom Simulating Reflector,简称BSR)是水合物底界的地震反射标志,其上部的振幅空白带是含水合物地层的反射特征,下部的高振幅异常区代表了下伏的游离气区(Free Gas Zones,简称FGZs)。利用高分辨率三维地震资料,精细描述了毛里塔尼亚滨海地区的BSR和FGZs的地震反射特征及其与周边沉积构造单元的关系。BSR在底辟构造上部出现上拱现象,在靠近峡谷两壁时BSR位置快速变深。据分析,在底辟构造带,沿断裂体系向上运移的热流体改变了此处的水合物稳定条件,导致水合物稳定底界向上变浅。而峡谷对周边沉积物的冷却作用使当地的水合物稳定条件发生与底辟构造带处相反的变化,导致水合物稳定底界向下发生移动,在地震上表现为BSR深度的增加。另外,研究发现BSR和FGZs在流体运移通道较发育的地区,如断层、气烟囱和底辟构造带地区更加发育,证明流体运移体系在该地区对水合物和FGZs的形成具有十分重要的作用,提供了水合物体系的气源供给。展开更多
Acoustic characteristics of a pulse detonation engine（PDE） with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional（2 D） non-splitting unstructured triangular me...Acoustic characteristics of a pulse detonation engine（PDE） with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional（2 D） non-splitting unstructured triangular mesh Euler solver based on the space-time conservation element and solution element（CE/SE） method is employed to simulate the flow field of a PDE.The numerical results clearly demonstrate the external flow field of the PDE. The effect of an ellipsoidal reflector on the flow field characteristic near the PDE exit is investigated. The formation process of reflected shock wave and reflected jet shock are reported in detail. An acoustic measurement system is established for the PDE acoustic testing. The experimental results show that the ellipsoidal reflector changes the sound waveform and directivity of PDE sound. The reflected shock wave and reflected jet shock result in two more positive pressure peaks in the sound waveform. The ellipsoidal reflector changes the directivity of PDE sound from 20 to 0. It is found that the peak sound pressure level（PSPL） and overall sound pressure level（OASPL） each obtain an increment when the PDE is installed with a reflector. The maximum relative increase ratio of PSPL and OASPL are obtained at the focus point F2, whose values are 6.1% and 6.84% respectively. The results of the duration of the PDE sound indicate that the reflecting and focusing wave generated by the reflector result in the increment of A duration and B duration before and near focus point F2. Results show that the ellipsoidal reflector has a great influence on the acoustic characteristic of PDE sound. The research is helpful for understanding the influence of an ellipsoidal reflector on the formation and propagation process of PDE sound.展开更多
Gas hydrates have been found in the western continental margin of South China Sea,which are revealed by widespread bottom simulating reflectors(BSRs)imaged from a three-dimensional(3D)seismic volume near the Guangle c...Gas hydrates have been found in the western continental margin of South China Sea,which are revealed by widespread bottom simulating reflectors(BSRs)imaged from a three-dimensional(3D)seismic volume near the Guangle carbonate platform in the western South China Sea.Fluid-escape structures(faults and gas chimneys)are originated below BSR were distinguished.A comprehensive model in three-level structure was proposed to depict the gas hydrate accumulation in the study area.In Level 1,regional major faults and gas chimneys provide the first pathways of upward migration of gas near basement.In Level 2,pervasive polygonal faults in carbonate layer promote the migration of gas.In Level 3,gases sourced from near-basement accumulate within shallow sediment layers and form gas hydrate above the unit with faults once appropriate temperature and pressure occur.The gas hydrates in the study area are mainly in microbial origin,and their accumulation occurs only when fluid-escape structures align in all the three levels.The proposed model of the gas hydrate accumulation in western SCS margin provides new insights for further studies in this poorly studied area.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supported by the National 973 Basic Research Program (Grant No. 2009CB219502)National Natural Science Foundation of China (Grant No. 41072084)
文摘BSR （Bottom Simulating Reflector） occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea （SCS）. It is an important seismic reference mark which identifies the gas hydrate and its distribution influenced by the tectonic movements. Single-point basin modeling was conducted using 473 points in the study area. To discuss the relationships between the tectonic subsidence and BSR, the volume and rate of tectonic subsidence in each geological time have been simulated. The results show that there are three tectonic accelerate subsidence processes in the study area since the late Miocene, especially since 1.8Ma the tectonic subsidence accelerates more apparently. Since the Late Miocene to Pleistocene, the rate of tectonic subsidence in deep-water underwent a transformation from weak to strong. The ratio of tectonic subsidence to the total subsidence was relatively high （65-70%）. Through the superposition of the BSR developed areas and the contours of tectonic subsidence in this area, it was discovered that more than 80% of BSR tend to be distributed at the slope break or depression-uplift structural transfer zone and the average tectonic subsidence rate ranges from 70 m/Ma to 125 m/Ma.
文摘拟海底反射层(Bottom Simulating Reflector,简称BSR)是水合物底界的地震反射标志,其上部的振幅空白带是含水合物地层的反射特征,下部的高振幅异常区代表了下伏的游离气区(Free Gas Zones,简称FGZs)。利用高分辨率三维地震资料,精细描述了毛里塔尼亚滨海地区的BSR和FGZs的地震反射特征及其与周边沉积构造单元的关系。BSR在底辟构造上部出现上拱现象,在靠近峡谷两壁时BSR位置快速变深。据分析,在底辟构造带,沿断裂体系向上运移的热流体改变了此处的水合物稳定条件,导致水合物稳定底界向上变浅。而峡谷对周边沉积物的冷却作用使当地的水合物稳定条件发生与底辟构造带处相反的变化,导致水合物稳定底界向下发生移动,在地震上表现为BSR深度的增加。另外,研究发现BSR和FGZs在流体运移通道较发育的地区,如断层、气烟囱和底辟构造带地区更加发育,证明流体运移体系在该地区对水合物和FGZs的形成具有十分重要的作用,提供了水合物体系的气源供给。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11372141 and 11472138)the National Defense Pre-Research Foundation of China(Grant No.61426040201162604002)
文摘Acoustic characteristics of a pulse detonation engine（PDE） with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional（2 D） non-splitting unstructured triangular mesh Euler solver based on the space-time conservation element and solution element（CE/SE） method is employed to simulate the flow field of a PDE.The numerical results clearly demonstrate the external flow field of the PDE. The effect of an ellipsoidal reflector on the flow field characteristic near the PDE exit is investigated. The formation process of reflected shock wave and reflected jet shock are reported in detail. An acoustic measurement system is established for the PDE acoustic testing. The experimental results show that the ellipsoidal reflector changes the sound waveform and directivity of PDE sound. The reflected shock wave and reflected jet shock result in two more positive pressure peaks in the sound waveform. The ellipsoidal reflector changes the directivity of PDE sound from 20 to 0. It is found that the peak sound pressure level（PSPL） and overall sound pressure level（OASPL） each obtain an increment when the PDE is installed with a reflector. The maximum relative increase ratio of PSPL and OASPL are obtained at the focus point F2, whose values are 6.1% and 6.84% respectively. The results of the duration of the PDE sound indicate that the reflecting and focusing wave generated by the reflector result in the increment of A duration and B duration before and near focus point F2. Results show that the ellipsoidal reflector has a great influence on the acoustic characteristic of PDE sound. The research is helpful for understanding the influence of an ellipsoidal reflector on the formation and propagation process of PDE sound.
基金Supported by the China Academy of Petroleum Exploration and Development(Nos.2019B-4909,2021DJ2401)Dr.Wei LI is specially funded by the CAS Pioneer Hundred Talents Program(No.Y8SL011001)。
文摘Gas hydrates have been found in the western continental margin of South China Sea,which are revealed by widespread bottom simulating reflectors(BSRs)imaged from a three-dimensional(3D)seismic volume near the Guangle carbonate platform in the western South China Sea.Fluid-escape structures(faults and gas chimneys)are originated below BSR were distinguished.A comprehensive model in three-level structure was proposed to depict the gas hydrate accumulation in the study area.In Level 1,regional major faults and gas chimneys provide the first pathways of upward migration of gas near basement.In Level 2,pervasive polygonal faults in carbonate layer promote the migration of gas.In Level 3,gases sourced from near-basement accumulate within shallow sediment layers and form gas hydrate above the unit with faults once appropriate temperature and pressure occur.The gas hydrates in the study area are mainly in microbial origin,and their accumulation occurs only when fluid-escape structures align in all the three levels.The proposed model of the gas hydrate accumulation in western SCS margin provides new insights for further studies in this poorly studied area.
