南海北部陆坡某海域浅层气的声学特征及其对水合物勘探的指示意义
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摘要
海底天然气渗漏是海洋环境中广泛分布的自然现象,在世界各大洋中都有发现。海底渗漏的气体赋存于浅部地层,可以改变近表层沉积物的物理性质,使其在声学剖面上得以反映。通过对南海北部陆坡某海域研究区浅地层剖面和地震数据分析,在浅地层剖面上发现了声空白、声混浊、增强反射层、速度下拉等特征,在地震剖面上则识别出气烟囱或泥底辟、亮点、速度下拉、增强反射层等特征。以似海底反射层(BSR)作为地震剖面上明显的含气层标志,划分了2套含气系统。通过浅地层剖面与地震剖面联合解释认为,BSR之下气烟囱/泥底辟的发育导致了亮点、速度下拉、增强反射层等声学特征的发生,BSR之上水合物层的存在则可能起到封堵天然气而使其发生侧向运移的作用,在气体封堵相对薄弱的位置,天然气向上运移形成声空白、声混浊、增强反射层、速度下拉等特征。以声空白代表的天然气聚集带可能成为块状水合物的发育场所,可能成为较有潜力的勘探目标。
Submarine gas seepage trapped in shallow strata occurs widely in the marine environment.It may change the physical properties of the sediment and leave some prints on the acoustic profiles.The sub-bottom profiles and multi-channel seismic reflection data collected from the northern slope of the South China Sea were processed and analyzed in this paper.Acoustic blank,acoustic turbidity,enhanced reflection and velocity pulling-down are discovered on sub-bottom profiles,and gas chimney or mud diapia,bright spot,velocity pulling-down and enhanced reflection on seismic profiles.The Bottom Simulating Reflector(BSR),indicator of gas occurrence on seismic profiles,is a boundary,which separate the gas system into two parts.The bright spot,velocity pulling-down and enhanced reflection caused by gas chimney or mud diapia,occur under the BSR,and the gas hydrate above the BSR may prevent gas migration upward,and force it to move laterally along the BSR.The continuous gas migration upward at the weak zone of the seal may cause the formation of acoustic blank,acoustic turbidity,enhanced reflection and velocity pulling-down.Therefore,the acoustic blank in the shallow strata,may be regarded as a right place for accumulation of block-hydrate and thus a potential exploration target.
Submarine gas seepage trapped in shallow strata occurs widely in the marine environment.It may change the physical properties of the sediment and leave some prints on the acoustic profiles.The sub-bottom profiles and multi-channel seismic reflection data collected from the northern slope of the South China Sea were processed and analyzed in this paper.Acoustic blank,acoustic turbidity,enhanced reflection and velocity pulling-down are discovered on sub-bottom profiles,and gas chimney or mud diapia,bright spot,velocity pulling-down and enhanced reflection on seismic profiles.The Bottom Simulating Reflector(BSR),indicator of gas occurrence on seismic profiles,is a boundary,which separate the gas system into two parts.The bright spot,velocity pulling-down and enhanced reflection caused by gas chimney or mud diapia,occur under the BSR,and the gas hydrate above the BSR may prevent gas migration upward,and force it to move laterally along the BSR.The continuous gas migration upward at the weak zone of the seal may cause the formation of acoustic blank,acoustic turbidity,enhanced reflection and velocity pulling-down.Therefore,the acoustic blank in the shallow strata,may be regarded as a right place for accumulation of block-hydrate and thus a potential exploration target.
引文
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[14]Chun J H,Ryu B J,Son B K,et al.Sediment mounds and other sedimentary features related to hydrate occurrence in a columnar seismic blanking zone of the Ulleung Basin,East Sea,Korea[J].Marine and Petroleum Geology,2011,28(10):1 787-1 800.
[15]杨木壮,吴能友,吴时国,等.南海北部陆坡特殊地质环境与BSR分布[M]∥李家彪,高抒.中国边缘海海盆演化与资源效应.北京:海洋出版社,2004.
[16]李家彪.中国边缘海形成演化与资源效应[M].北京:海洋出版社,2005.
[17]张光学,祝有海,徐华宁.非活动大陆边缘的天然气水合物及其成藏过程述评[J].地质论评,2003,49(2):181-186.
[18]沙志彬,杨木壮,梁劲,等.南海北部陆坡海底异常地貌特征与天然气水合物的关系[J].南海地质研究,2003(14):29-34.
[19]王秀娟,吴时国.琼东南盆地块体搬运体系对天然气水合物形成的控制作用[J].海洋地质与第四纪地质,2011,31(1):109-118.
[20]倪玉根,郑玉龙,李守军.南海神狐海域上陆坡区典型浅地层剖面的初步解释[J].海洋学研究,2009,27(1):30-36.
[21]李守军,初凤友,方银霞.南海北部陆坡神狐海域浅地层与单道地震剖面联合解释——水合物区沉积地层特征[J].热带海洋学报,2010,29(4):56-62.
[22]黄永样,Erwin Suess,吴能友,等.南海北部陆坡甲烷和天然气水合物地质——中德合作SO-177航次成果专报[M].北京:地质出版社,2008.
[23]Yun J W,Orange D L.Subsurface gas off shore of northern California and its link to submarine geomorphology[J].Marine Geology,1999,154:357-368.
[24]李双林,董贺平,肖菲.海底烃类渗漏的地球物理识别[J].海洋地质动态,2007,23(11):14-21.
[25]Missiaen T,Murphy S,Lonckea L,et al.Very high-resolution seismic mapping of shallow gas in the Belgian coastal zone[J].Continental Shelf Research,2002,22:2 291-2 301.
[26]李列,宋海斌.莺歌海盆地中央坳陷带海底天然气渗漏系统初探[J].地球物理学进展,2006,21(4):1 244-1 247.
[27]刘宝明,牛滨华,孙春岩,等.南海北部陆缘晚期油气成藏机理及动力学过程[J].石油实验地质,2007,29(5):441-445.
[28]Sloan E D,Koh C.Clathrates hydrates of natural gases[M].New York:Marcel Dekker,1998.
[2]Judd A,Hovland M.Seabed fluid flow:the impact of geology,biology and the marine environment[M].Oxford:Cambridge University Press,2007.
[3]Greinert J,Lewis K B,Bialas J.Methane seepage along the Hikurangi Margin,New Zealand:overview of studies in 2006and 2007and new evidence from visual,bathymetric and hydroacoustic investigations[J].Marine Geology,2010,272:6-25.
[4]Suess E.Marine gas hydrate research:changing views over the past 25years[C].Proceedings of the 7th International Conference on Gas Hydrates(ICGH 2011),2011.
[5]Milkov A V.Worldwide distribution of submarine mud volcanoes and associated gas hydrates[J].Marine Geology,2000,167:29-42.
[6]Milkov A V,Sassen R.Preliminary assessment of resources and economic potential of individual gas hydrate accumulations in the Gulf of Mexico continental slope[J].Marine and Petroleum Geology,2003,20:111-128.
[7]陈林,宋海滨.海底天然气渗漏的地球物理特征及识别方法[J].地球物理学进展,2005,20(4):1 067-1 073.
[8]Sager W W,Lee C S,Mandonald I R,et al.High frequency near bottom acoustic reflection signature of hydrocarbon seeps on the Northern Gulf of Mexico continental slope[J].Geo-Marine Letters,1999,18:267-276.
[9]Hovland M,Judd A G.Seabed pockmarks and seepages:impact on the geology,biology and the marine environment[M].London:Graham and Trotman,1988.
[10]Garcia-Gil S,Vilas F,Garcia-Garcia A.Shallow gas features in incised-valley fills(Ría de Vigo,NW Spain):a case study[J].Continental Shelf Research,2002,22(16):2 303-2 315.
[11]Casas D,Ercilla G,Baraza J.Acoustic evidences of gas in the continental slope sediments of the Gulf of Cadiz(E Atlantic)[J].Geo-Marine Letter,2003,23:300-310.
[12]Naudts L,De Batist M.Geo-and hydro-acoustic manifestations of shallow gas and gas seeps in the Dnepr paleodelta,northwestern Black Sea[J].The Leading Edge,2009,28(9):1 030-1 040.
[13]Jones A T,Greinert J,Bowden D A,et al.Acoustic and visual characterization of methane-rich seabed seeps at Omakere Ridge on the Hikurangi Margin,New Zealand[J].Marine Geology,2010,272(1/4):154-169.
[14]Chun J H,Ryu B J,Son B K,et al.Sediment mounds and other sedimentary features related to hydrate occurrence in a columnar seismic blanking zone of the Ulleung Basin,East Sea,Korea[J].Marine and Petroleum Geology,2011,28(10):1 787-1 800.
[15]杨木壮,吴能友,吴时国,等.南海北部陆坡特殊地质环境与BSR分布[M]∥李家彪,高抒.中国边缘海海盆演化与资源效应.北京:海洋出版社,2004.
[16]李家彪.中国边缘海形成演化与资源效应[M].北京:海洋出版社,2005.
[17]张光学,祝有海,徐华宁.非活动大陆边缘的天然气水合物及其成藏过程述评[J].地质论评,2003,49(2):181-186.
[18]沙志彬,杨木壮,梁劲,等.南海北部陆坡海底异常地貌特征与天然气水合物的关系[J].南海地质研究,2003(14):29-34.
[19]王秀娟,吴时国.琼东南盆地块体搬运体系对天然气水合物形成的控制作用[J].海洋地质与第四纪地质,2011,31(1):109-118.
[20]倪玉根,郑玉龙,李守军.南海神狐海域上陆坡区典型浅地层剖面的初步解释[J].海洋学研究,2009,27(1):30-36.
[21]李守军,初凤友,方银霞.南海北部陆坡神狐海域浅地层与单道地震剖面联合解释——水合物区沉积地层特征[J].热带海洋学报,2010,29(4):56-62.
[22]黄永样,Erwin Suess,吴能友,等.南海北部陆坡甲烷和天然气水合物地质——中德合作SO-177航次成果专报[M].北京:地质出版社,2008.
[23]Yun J W,Orange D L.Subsurface gas off shore of northern California and its link to submarine geomorphology[J].Marine Geology,1999,154:357-368.
[24]李双林,董贺平,肖菲.海底烃类渗漏的地球物理识别[J].海洋地质动态,2007,23(11):14-21.
[25]Missiaen T,Murphy S,Lonckea L,et al.Very high-resolution seismic mapping of shallow gas in the Belgian coastal zone[J].Continental Shelf Research,2002,22:2 291-2 301.
[26]李列,宋海斌.莺歌海盆地中央坳陷带海底天然气渗漏系统初探[J].地球物理学进展,2006,21(4):1 244-1 247.
[27]刘宝明,牛滨华,孙春岩,等.南海北部陆缘晚期油气成藏机理及动力学过程[J].石油实验地质,2007,29(5):441-445.
[28]Sloan E D,Koh C.Clathrates hydrates of natural gases[M].New York:Marcel Dekker,1998.
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