天然气水合物层和游离气层的地震反演识别——布莱克海台USGS95-1测线应用实例
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摘要
利用基于弹性波阻抗的AVO反演方法对美国布莱克海台实际水合物存在区域的USGS95-1测线进行处理,得到了地震纵波波阻抗和横波波阻抗,并据此计算出泊松比和拉梅系数等弹性参数。对反演得到的各弹性参数分析发现:与同沉积的水饱和地层相比,含水合物的地层具有高的波阻抗和拉梅系数;而游离气层具有低的纵波波阻抗、泊松比和拉梅系数。据此推断出该测线上水合物层和游离气层的分布范围。认为波阻抗剖面和拉梅系数剖面上的近似平行于海底的高值带指示水合物层,且水合物层下伏所圈闭的低泊松比和低纵波波阻抗区域指示游离气的存在;还发现该条测线上的BSR主要是由其下的游离气的聚集引起。
Compressional-wave impedance and shear-wave impedance of line USGS95-1 from Blake Ridge are obtained using elastic-impedance inversion method.Also,they are used to calculate Possion's ratio and Lame parameter of this line.All these elastic parameters are analyzed to identify the gashydrate sediments and free gas layer.The results show that the impedance and Lame parameter of the sediments containing gas hydrates are higher than those of the media with saturated water at the same depth,but for free gas layer,these two kinds of elastic parameters,with Possion's ratio,become very low.Therefore,the gas-hydrate area and free gas area can be outlined respectively according to these characteristics.The zone of paralleling bottom with high impedance and Lame parameter indicates the gas-hydrate layer,and the area with low impedance and Possion's ratio trapped by gas-hydrate layer below it symbolizes the accumulation of free gas.The analysis also shows the main factor that causes the BSR of this line is the free gas below it.
Compressional-wave impedance and shear-wave impedance of line USGS95-1 from Blake Ridge are obtained using elastic-impedance inversion method.Also,they are used to calculate Possion's ratio and Lame parameter of this line.All these elastic parameters are analyzed to identify the gashydrate sediments and free gas layer.The results show that the impedance and Lame parameter of the sediments containing gas hydrates are higher than those of the media with saturated water at the same depth,but for free gas layer,these two kinds of elastic parameters,with Possion's ratio,become very low.Therefore,the gas-hydrate area and free gas area can be outlined respectively according to these characteristics.The zone of paralleling bottom with high impedance and Lame parameter indicates the gas-hydrate layer,and the area with low impedance and Possion's ratio trapped by gas-hydrate layer below it symbolizes the accumulation of free gas.The analysis also shows the main factor that causes the BSR of this line is the free gas below it.
引文
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[3]杨涛,蒋少涌,杨竞红,等.孔隙水中NH4+和HPO42-浓度异常:一种潜在的天然气水合物地球化学勘查新指标[J].现代地质,2005,19(1):55-60.
[4]牛滨华,孙春岩,苏新,等.勘查地球化学方法适用于勘查天然气水合物的依据[J].现代地质,2005,19(1):61-66.
[5]刘海生,王南萍,侯胜利,等.海洋沉积物热释光———潜在的天然气水合物找矿方法[J].物探与化探,2002,26(4):264-267.
[6]王宏斌,梁劲,龚跃华,等.基于天然气水合物地震数据计算南海北部陆坡海底热流[J].现代地质,2005,19(1):67-73.
[7]卢振权,吴必豪,强祖基.利用卫星热红外遥感探测南海天然气水合物[J].地质学报,2002,76(1):100-106.
[8]卢振权,吴必豪,强祖基,等.中国近海海域卫星热红外亮温增温异常探讨[J].现代地质,2005,19(1):74-82.
[9]Shipley TH,Houston MH.Seismic reflection evidence for wide-spread occurrence of possible gas-hydrate horizons on continentalslopes and rises[J].AAPG Bulletin,1979,63(12):2204-2213.
[10]Holbrook W S,Hoskins H.Methane hydrate and free gas on theBlake Ridge from vertical seismic profile[J].Science,1996,273:1840-1843.
[11]孙春岩,黄新武,章明昱,等.天然气水合物及其地球物理识别方法的研究进展[J].现代地质,2003,17(2):195-201.
[12]Li Minfeng,Liu Xuewei.An AVO inversion method for identif-ying gas hydrate and free gas[M]//SEGJ.The 7th SEGJ In-ternational Symposium.Sendai,Japan:Society of ExplorationGeophysicists of Japan,2004:72-77.
[13]李敏锋,李灿苹,刘学伟,等.基于小波变换的天然气水合物层地震数据多尺度分析———布莱克海台USGS95-1测线应用实例[J].现代地质,2006,20(1):109-114.
[14]刘学伟,李敏锋,张聿文,等.天然气水合物地震响应研究———中国南海HD152测线[J].现代地质,2005,19(1):33-38.
[15]Patrick Connolly.Elastic impedance[J].The Leading Edge,1999,18(6):438-452.
[16]Lu Shaoming,George A Mcmechan.Elastic impedance inversionof multichannel seismic data from unconsolidated sediments con-taining gas hydrate and free gas[J].Geophysics,2004,69(1):164-179.
[17]ODP Leg 164 Shipboard Scientific Party.Methane gas hydratedrilled at Blake Ridge[J].Eos Transactions,American Geo-physical Union,1996,77(23):219.
[18]Eker C,Dvorkin J,Nur A.Sediments with gas hydrates:Internalstructure from seismic AVO[J].Geophysics,1998,63(5):1659-1669.
[19]Biot MA.Theory of propagation of elastic waves in a fluid-satu-rated porous solid[J].Journal of the Acoustical Society of A-merica,1956,28:168-178.
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