南海东北部973剖面BSR及其热流特征
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摘要
对南海东北部973项目采集的地震测线进行了处理,阐明了恒春海脊处天然气水合物似海底反射(BSR)的特征.不同类型剖面的分析表明,单道地震剖面可以揭示南海东北部地区BSR一定的分布,但地震处理对揭示BSR分布全貌起重要作用.南海东北部的BSR具有世界大陆边缘BSR典型的特征,切穿了沉积层理反射,与海底起伏大体平行,为一强振幅的负极性反射.该BSR特征明显,意味着南海东北部地区存在含天然气水合物沉积.利用甲烷水合物与多组分天然气水合物相平衡曲线,计算了稳定带底界的埋深,并与BSR深度进行了对比分析.无论是甲烷水合物稳定带底界还是多组分天然气水合物稳定带的底界,单一地温梯度计算的结果不可能与BSR深度在整个剖面上对应.可知本区横向上地温梯度变化较大.利用BSR资料估算了地温梯度并求得热流值.计算表明,地温梯度与热流值由西向东,随着离海沟距离的增大、离岛弧距离的减小而减小.BSR计算得到的热流值为28~64 mW/m2,与台湾西南实测热流值的结果基本可以对比.
Processing of a recently acquired seismic line in the northeastern South China Sea by Project 973 has been conducted to study the character and the distribution of gas hydrate Bottom-Simulating Reflectors(BSRs) in the Hengchun ridge.Analysis of different-type seismic profiles shows that the distribution of BSRs can be revealed to some extents by single-channel profile in this area,but seismic data processing plays an important role to resolve the full distribution of BSRs in this area.BSR's in the northeastern South China Sea have the typical characteristics of BSRs on worldwide continental margins: they cross sediment bed reflections,they are generally parallel to the seafloor and the associated reflections have strong amplitude and a negative polarity.The characteristics of BSRs in this area are obvious and the BSRs indicate the occurrence of gas hydrate-bearing sediments in the northeastern South China Sea.The depth of the base of the gas-hydrate stability zone was calculated using the phase stability boundary curve of methane hydrate and gas hydrate with mixture gas composition and compared with the observed BSR depth.If a single gradient geothermal curve is used for the calculation,the base of the stability zone for methane hydrate or gas hydrate with a gas mixture composition does not correspond to the depth of the BSRs observed along the whole seismic profile.The geothermal gradient therefore changes significantly along the profile.The geothermal gradient and heat flow were estimated from the BSR data and the calculations show that the geothermal gradient and heat flow decrease from west to east,with the increase of the distance from the trench and the decrease of the distance to the island arc.The calculated heat flow changes from 28 to 64 mW/m~2,which is basically consistent with the measured heat flow in southwestern offshore Taiwan.
Processing of a recently acquired seismic line in the northeastern South China Sea by Project 973 has been conducted to study the character and the distribution of gas hydrate Bottom-Simulating Reflectors(BSRs) in the Hengchun ridge.Analysis of different-type seismic profiles shows that the distribution of BSRs can be revealed to some extents by single-channel profile in this area,but seismic data processing plays an important role to resolve the full distribution of BSRs in this area.BSR's in the northeastern South China Sea have the typical characteristics of BSRs on worldwide continental margins: they cross sediment bed reflections,they are generally parallel to the seafloor and the associated reflections have strong amplitude and a negative polarity.The characteristics of BSRs in this area are obvious and the BSRs indicate the occurrence of gas hydrate-bearing sediments in the northeastern South China Sea.The depth of the base of the gas-hydrate stability zone was calculated using the phase stability boundary curve of methane hydrate and gas hydrate with mixture gas composition and compared with the observed BSR depth.If a single gradient geothermal curve is used for the calculation,the base of the stability zone for methane hydrate or gas hydrate with a gas mixture composition does not correspond to the depth of the BSRs observed along the whole seismic profile.The geothermal gradient therefore changes significantly along the profile.The geothermal gradient and heat flow were estimated from the BSR data and the calculations show that the geothermal gradient and heat flow decrease from west to east,with the increase of the distance from the trench and the decrease of the distance to the island arc.The calculated heat flow changes from 28 to 64 mW/m~2,which is basically consistent with the measured heat flow in southwestern offshore Taiwan.
引文
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[6]Shyu C-T,Hsu S-K,Liu C-S.Heat flows off southwest Taiwan:measurements over mud diapers and estimated from bottom simulatingreflectors.Terrestrial Atmospheric Ocean Sciences,1998,9:795~812
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[11]Sloan Jr E D.Clathrate Hydrates of Natural Gases.New York:Marcel Dekker,1998.705
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[13]Ganguly N,Spence G D,Chapman N R.Heat flow variations frombottom simulating reflectors on the Cascadia margin.Marine Geology,2000,164:53~68
[14]Kaul N,Rosenberger A,Villinger H.Comparison of measured andBSR-derived heat flow values,Makran accretionary prism,Pakistan.Marine Geology,2000,164:37~51
[15]Davis E E,Hyndman R D,Villinger H.Rates of fluid expulsionacross the northern Cascadia accretionary prism:constraints from newheat flow and multichannel seismic reflection data.J.Geophys.Res.,1990,95:8869~8889
[16]Ashi J,Tokuyama H,Taira A.Distribution of methane hydrate BSRsand its implication for the prism growth in the Nankai Trough.MarineGeology,2002,187:177~191
[17]宋海斌,吴能友,吴时国等.南海东北部973剖面地震资料处理及其BSR特征.见:李家彪,高抒主编.中国边缘海海盆演化与资源效应.北京:海洋出版社,2004.182~185Song H B,Wu N Y,Wu S G,et al.Seismic data processing of one973 profile and its BSR characteristics in northeastern South ChinaSea.In:Li J B,Gao S eds.Sea-basin Evolution and Resources ofChinese Marginal Seas(in Chinese).Beijing:Ocean Press,2004.182~185
[18]邓辉,阎贫,刘海龄.台湾西南海域似海底反射分析.热带海洋学报,2005,24(2):79~85Deng H,Yan P,Liu H L.An analysis on bottom simulating reflectorsin southwest Taiwan sea area.Journal of Tropical Oceanography(inChinese),2005,24(2):79~85
[19]丁巍伟,陈汉林,王渝民等.台湾增生楔天然气水合物的地震特征.海洋与湖沼,2006,37(1):90~96Ding W W,Chen H L,Wang Y M,et al.Geophysical features of gashydrate in Taiwan accretionary prism,South China Sea.Oceanologiaet Limnologia Sinica(in Chinese),2006,37(1):90~96
[20]姚伯初.南海北部陆缘天然气水合物初探.海洋地质与第四纪地质,1998,18(4):11~18Yao B C.Preliminary survey of gas hydrates in north of South ChinaSea.Mar.Geol.&Quaternary Geol.(in Chinese),1998,18(4):11~18
[21]宋海斌,耿建华,Wong How-Kin等.南海北部东沙海域天然气水合物的初步研究.地球物理学报,2001,44(5):687~695Song H B,Geng J H,Wong H-K,et al.A preliminary study of gashydrates in Dongsha region north of South China Sea.Chinese J.Geophys.(in Chinese),2001,44(5):687~695
[22]张光学,黄永样,祝有海等.南海天然气水合物的成矿远景.海洋地质与第四纪地质,2002,22(1):75~81Zhang G X,Huang Y Y,Zhu Y H,et al.Prospect of gas hydrateresources in the South China Sea.Mar.Geol.&Quaternary Geol.(in Chinese),2002,22(1):75~81
[23]Wu S,Zhang G,Huang Y,et al.Gas hydrate occurrence on thecontinental slope of the northern South China Sea.Marine andPetroleum Geology,2005,22:403~412
[2]陈多福,李绪宣,夏斌.南海琼东南盆地天然气水合物稳定域分布特征及资源预测.地球物理学报,2004,47(3):483~489Chen D F,Li X X,Xia B.Distribution of gas hydrate stable zonesand resource prediction in the Qiongdongnan Basin of the South ChinaSea.Chinese J.Geophys.(in Chinese),2004,47(3):483~489
[3]陈多福,王茂春,夏斌.青藏高原冻土带天然气水合物的形成条件与分布预测.地球物理学报,2005,48(1):165~172Chen D F,Wang M C,Xia B.Formation condition and distributionprediction of gas hydrate in Qinghai-Tibet Plateau permafrost.Chinese J.Geophys.(in Chinese),2005,48(1):165~172
[4]Chi W C,Reed D L,Liu C S,et al.Distribution of the bottomsimulating reflector in the offshore Taiwan collision area.TerrestrialAtmospheric Ocean Sciences,1998,9:779~794
[5]Chow J,Lee J S,Liu C S,et al.Characteristics of the bottomreflectors near mud diapers:offshore southwestern Taiwan.Geo-Marine Letters,2000,20:3~9
[6]Shyu C-T,Hsu S-K,Liu C-S.Heat flows off southwest Taiwan:measurements over mud diapers and estimated from bottom simulatingreflectors.Terrestrial Atmospheric Ocean Sciences,1998,9:795~812
[7]McDonnell S L,Max M D,Cherkis N Z,et al.Tectono-sedimentarycontrols on the likelihood of gas hydrate occurrence near Taiwan.Marine and Petroleum Geology,2000,17:929~936
[8]He L,Wang K,Xiong L,et al.Heat flow and the thermal history ofthe South China Sea.Physics of the Earth and Planetary Interiors,2001,126:211~220
[9]Miles P R.Potential distribution of methane hydrate beneath theEuropean continental margins.Geophys.Res.Lett.,1995,22:3179~3182
[10]Rao Y H.C-program for the calculation of gas hydrate stability zonethickness.Computers&Geosciences,1999,25:705~707
[11]Sloan Jr E D.Clathrate Hydrates of Natural Gases.New York:Marcel Dekker,1998.705
[12]Yamano M,Uyeda R M,Aoki Y,et al.Estimates of heat flow derivedfrom gas hydrates.Geology,1982,10:339~343
[13]Ganguly N,Spence G D,Chapman N R.Heat flow variations frombottom simulating reflectors on the Cascadia margin.Marine Geology,2000,164:53~68
[14]Kaul N,Rosenberger A,Villinger H.Comparison of measured andBSR-derived heat flow values,Makran accretionary prism,Pakistan.Marine Geology,2000,164:37~51
[15]Davis E E,Hyndman R D,Villinger H.Rates of fluid expulsionacross the northern Cascadia accretionary prism:constraints from newheat flow and multichannel seismic reflection data.J.Geophys.Res.,1990,95:8869~8889
[16]Ashi J,Tokuyama H,Taira A.Distribution of methane hydrate BSRsand its implication for the prism growth in the Nankai Trough.MarineGeology,2002,187:177~191
[17]宋海斌,吴能友,吴时国等.南海东北部973剖面地震资料处理及其BSR特征.见:李家彪,高抒主编.中国边缘海海盆演化与资源效应.北京:海洋出版社,2004.182~185Song H B,Wu N Y,Wu S G,et al.Seismic data processing of one973 profile and its BSR characteristics in northeastern South ChinaSea.In:Li J B,Gao S eds.Sea-basin Evolution and Resources ofChinese Marginal Seas(in Chinese).Beijing:Ocean Press,2004.182~185
[18]邓辉,阎贫,刘海龄.台湾西南海域似海底反射分析.热带海洋学报,2005,24(2):79~85Deng H,Yan P,Liu H L.An analysis on bottom simulating reflectorsin southwest Taiwan sea area.Journal of Tropical Oceanography(inChinese),2005,24(2):79~85
[19]丁巍伟,陈汉林,王渝民等.台湾增生楔天然气水合物的地震特征.海洋与湖沼,2006,37(1):90~96Ding W W,Chen H L,Wang Y M,et al.Geophysical features of gashydrate in Taiwan accretionary prism,South China Sea.Oceanologiaet Limnologia Sinica(in Chinese),2006,37(1):90~96
[20]姚伯初.南海北部陆缘天然气水合物初探.海洋地质与第四纪地质,1998,18(4):11~18Yao B C.Preliminary survey of gas hydrates in north of South ChinaSea.Mar.Geol.&Quaternary Geol.(in Chinese),1998,18(4):11~18
[21]宋海斌,耿建华,Wong How-Kin等.南海北部东沙海域天然气水合物的初步研究.地球物理学报,2001,44(5):687~695Song H B,Geng J H,Wong H-K,et al.A preliminary study of gashydrates in Dongsha region north of South China Sea.Chinese J.Geophys.(in Chinese),2001,44(5):687~695
[22]张光学,黄永样,祝有海等.南海天然气水合物的成矿远景.海洋地质与第四纪地质,2002,22(1):75~81Zhang G X,Huang Y Y,Zhu Y H,et al.Prospect of gas hydrateresources in the South China Sea.Mar.Geol.&Quaternary Geol.(in Chinese),2002,22(1):75~81
[23]Wu S,Zhang G,Huang Y,et al.Gas hydrate occurrence on thecontinental slope of the northern South China Sea.Marine andPetroleum Geology,2005,22:403~412
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