海洋可控源电磁法空气波研究现状及展望
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摘要
海洋可控源电磁法是钻前储层评价的有效手段,它可作为海洋地震重要辅助手段识别海底构造的储油/储水特征,从而减少盲钻率和勘探成本。然而,当使用水平电偶极作为发射源在浅水区测量时,沿空气-海水分界面传播的空气波会完全掩盖从高阻储油层返回的有用信号。由于空气波不含海底储油层的任何信息,空气波的存在严重影响海洋电磁的应用。因此,如何在浅水区观测数据中去除空气波影响以取得好的反演结果成为当前海洋电磁法的研究热点之一。首先基于Weidelt的空气波理论并采用对TE谱核直接求导的方法推导出空气波的主导项,然后根据空气波的物理成因及影响特征阐述了海洋电磁数据解释之前必须去除空气波的原因,最后将目前处理空气波问题的方法分成3类:1)根据空气波在频率域和时间域的特性去除或压制空气波,2)采用无空气波的测量方式,3)直接对含空气波的电磁数据进行反演解释。通过比较各种方法的效果,发现所有方法都有自己的应用条件和局限性。为有效地压制和去除空气波,各种方法的组合也许有更好的应用效果。
Marine controlled-source electromagnetic method(MCSEM) is an effective technology for pre-drill reservoir appraisal.It is an important auxiliary technology for marine seismic to distinguish between oil-and water-bearing reservoir and consequently reduces the risk of dry wells and exploration cost.However,when surveying in shallow water using a horizontal electrical dipole(HED) as transmitting source,the airwave,propagating at the air-ocean interface,will almost totally mask the signal from the resistive reservoir.Due to the fact that the airwave doesn't contain any information about the resistive layer,it seriously affects the MCSEM application in shallow water.Therefore,removal of the airwave from MCSEM data to get a good inversion result becomes a research focus.Based on Weidelt's(2007) airwave theory,we first get the leading term of airwave by derivation of spectral kernels of TE mode.We then,discuss the reason for airwave removal before MCSEM inversion by elaborating the mechanism of its origin and effects.Finally,we divide the current technologies dealing with airwave problem into three categories: 1)Remove airwave based on its characteristics in frequency-domain and time-domain;2)Airwave-free survey;3)Direct interpretation.After analyzing these technologies,we find that all current technologies cannot completely remove the airwave effect in MCSEM data.Each method has its own conditions and limitations for application.A combination of these methods is more helpful and effective.
Marine controlled-source electromagnetic method(MCSEM) is an effective technology for pre-drill reservoir appraisal.It is an important auxiliary technology for marine seismic to distinguish between oil-and water-bearing reservoir and consequently reduces the risk of dry wells and exploration cost.However,when surveying in shallow water using a horizontal electrical dipole(HED) as transmitting source,the airwave,propagating at the air-ocean interface,will almost totally mask the signal from the resistive reservoir.Due to the fact that the airwave doesn't contain any information about the resistive layer,it seriously affects the MCSEM application in shallow water.Therefore,removal of the airwave from MCSEM data to get a good inversion result becomes a research focus.Based on Weidelt's(2007) airwave theory,we first get the leading term of airwave by derivation of spectral kernels of TE mode.We then,discuss the reason for airwave removal before MCSEM inversion by elaborating the mechanism of its origin and effects.Finally,we divide the current technologies dealing with airwave problem into three categories: 1)Remove airwave based on its characteristics in frequency-domain and time-domain;2)Airwave-free survey;3)Direct interpretation.After analyzing these technologies,we find that all current technologies cannot completely remove the airwave effect in MCSEM data.Each method has its own conditions and limitations for application.A combination of these methods is more helpful and effective.
引文
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[14]Zhdanov M S,Cuma M,Wilson G A,et al.Iterative Electromagnetic Migration for3DInversion of Marine Controlled-Source Electromagnetic Data[J].Geo-physical Prospecting,2011,59:1101-1113.
[15]Andréis D,MacGregor L.Controlled-Source Electro-magnetic Sounding in Shallow Water:Principles and Applications[J].Geophysics,2008,73(1):F21-F32.
[16]Weiss C J.The Fallacy of the“Shallow-Water Prob-lem”in Marine CSEM Exploration[J].Geophysics,2007,72(6):A93-A97.
[17]Wait J R.The Electromagnetic Fields of A Horizon-tal Dipole in the Presence of a Conducting Half-Space[J].Can J Phys,1961,39:1017-1028.
[18]Bannister P R.New Simplified Formulas for ELF Subsurface to Subsurface Propagation[J].IEEE J Ocean Eng,1984,9:154-163.
[19]King R W P,Owens M,Wu T T.Lateral Electro-magnetic Waves[M].New York:Springer-Verlag,1992.
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[21]Um E S,Alumbaugh D L.On the Physics of the Ma-rine Controlled-Source Electromagnetic Method[J].Geophysics,2007,72(2):WA13-WA26.
[22]Weidelt P.Guided Waves in Marine CSEM[J].Geo-phys J Int,2007,171:153-176.
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[24]Lφseth L O,Amundsen L,Jenssen A J K.A Solu-tion to the Airwave-Removal Problem in Shallow-Wa-ter Marine EM[J].Geophysics,2010,75(5):A37-A42.
[25]Hunziker J,Slob E,Mulder W.Effects of the Air-wave in Time-Domain Marine Controlled-Source Elec-tromagnetics[J].Geophysics,2011,76(4):F251-F261.
[26]Constable S C.Method and System for Seafloor Geo-logical Survey Using Vertical Electric Field Measure-ment:U S,WO2003104844[P].2003-12-18.
[27]Holten T,Flekky E G,Singer B,et al.Vertical Source,Vertical Receiver,Electromagnetic Tech-nique for Offshore Hydrocarbon Exploration[J].First Break,2009,27:89-93.
[28]Dell’Aversana P.Improving Interpretation of CSEM in Shallow Water[J].TLE,2007:332-335.
[29]Frenkel M,Davydycheva S.A Modeling Study of Low-Frequency CSEM in Shallow Water[C]//71st Annual International Conference&Exhibition.Am-sterdam:EAGE,2009:075.
[30]Li Y G,Constable S.Transient Electromagnetic in Shallow Water:Insights from1D Modeling[J].Chi-nese J Geophys,2010,53:737-742.
[31]Wait J R,Campbell L L.The Fields of an Electric Dipole in a Semi-Infinite Conducting Medium[J].J Geophys Res,1953,58:21-28.
[32]Wait J R,Campbell L L.The Fields of an Oscillating Magnetic Dipole Immersed in a Semi-Infinite Conduc-ting Medium[J].J Geophys Res,1953,58:167-178.
[33]Weaver J T.The Quasi-Static Field of an Electric Di-pole Embedded in a Two-Layer Conducting Half-Space[J].Can J Phys,1967,45:1971-2002.
[34]Bannister P R.Quasi-Static Fields of Dipole Anten-nas at Earth’s Surface[J].Radio Sci,1966,1:1321-1330.
[35]Bannister P R,Hart W C.Quasi-Static Fields of Di-pole Antennas Below the Earth’s Surface[R].New London:Naval Underwater Systems Center,1968.
[36]Nordskag J,Amundsen L.Asymptotic Airwave Mo-deling for Marine Controlled Source Electromagnetic Surveying[J].Geophysics,2007,72(6):F249-F255.
[37]Yin C.Electromagnetic Induction in a Layered Con-ductor with Arbitrary Anisotropy[D].Braun-schweig:Technical University Braunschweig,1999.
[38]Lu X,Srnka L J,Carazzone J J.Method for Remo-ving Air Wave Effect from Offshore Frequency Do-main Controlled-Source Electromagnetic Data:U S,WO2005/010560[P].2005-02-03.
[39]Ursin B.Review of Elastic and Electromagnetic Wave Propagation in Horizontally Layered Media[J].Geo-physics,1983,48:1063-1081.
[40]Levy S,Oldenburg D,Wang J.Subsurface Imaging Using Magnetotelluric Data[J].Geophysics,1988,53:104-117.
[41]Zhdanov M S,Traynin P,Booker J R.Underground Imaging by Frequency-Domain Electromagnetic Mi-gration[J].Geophysics,1996,61:666-682.
[42]Van den Berg P M,Abubakar A,Habashy T.Re-moving Sea Surface-Related Electromagnetic Fields in Performing an Electromagnetic Survey:U S,WO/2008/054888[P].2008-09-30.
[43]Chen J P,Alumbaugh D L.Three Methods for Miti-gating Airwaves in Shallow Water Marine Controlled-Source Electromagnetic Data[J].Geophysics,2011,76(2):F89-F99.
[44]Maaφ F A,Nguyen A K.Enhanced Subsurface Re-sponse for Marine CSEM Surveying[J].Geophysics,2010,75(3):A7-A10.
[45]Wirianto M,Mulder W A,Slob E C.Exploiting the Airwave for Time-Lapse Reservoir Monitoring with CSEM on Land[J].Geophysics,2011,76(3):A15-A19.
[46]Mittet R.Normalized Amplitude Ratios for Frequen-cy-Domain CSEM in Very Shallow Water[J].First Break,2008,26(11):47-54.
[47]Ziolkowski A,Wright D.Removal of the Airwave in Shallow Marine Transient EM Data[C]//77th Annual International Meeting.San Antonio:SEG,2007:534-538.
[2]Edwards N.Marine Controlled Source Electromagne-tics:Principles,Methodologies,Future Commercial Applications[J].Surv Geophys,2005,26:675-700.
[3]何展翔,孙卫斌,孔繁恕,等.海洋电磁法[J].石油地球物理勘探,2006,41(4):451-457.He Zhan-xiang,Sun Wei-bin,Kong Fan-su,et al.Marine Electromagnetic Method[J].Oil Geophysical Prospecting,2006,41(4):451-457.
[4]Srnka L J,Carazzone J J,Ephron M S,et al.Remote Reservoir Resistivity Mapping[J].The Leading Edge,2006,25:972-975.
[5]Constable S,Srnka L J.An Introduction to Marine Controlled Source Electromagnetic Methods for Hy-drocarbon Exploration[J].Geophysics,2007,72(3):WA3-WA12.
[6]Constable S.Ten Years of Marine CSEM for Hydro-carbon Exploration[J].Geophysics,2010,75(5):75A67-75A81.
[7]Chave A D,Cox C S.Controlled Electromagnetic Sou-rces for Measuring Electrical Conductivity Beneath Oceans:Part1:Forward Problem and Model Study[J].Journal of Geophysical Research,1982,87(B7):5327-5338.
[8]Constable S,Weiss C J.Mapping Thin Resistors and Hydrocarbons with Marine EM Methods:Insights from1D Modeling[J].Geophysics,2006,71(2):G43-G51.
[9]Weiss C J,Constable S.Mapping Thin Resistors and Hydrocarbons with Marine EM Methods:Part2:Modeling and Analysis in3D[J].Geophysics,2006,71(6):G321-G332.
[10]Lφseth L O,Ursin B.Electromagnetic Fields in Pla-narly Layered Anisotropic Media[J].Geophys J Int,2007,170:44-80.
[11]Li Y G,Key K.2D Marine Controlled-Source Elec-tromagnetic Modeling:Part1:An Adaptive Finite-El-ement Algorithm[J].Geophysics,2007,72(2):WA51-WA62.
[12]Key K.1DInversion of Multicomponent,Multifre-quency Marine CSEM Data:Methodology and Syn-thetic Studies for Resolving Thin Resistive Layers[J].Geophysics,2009,74(2):F9-F20.
[13]付长民,底青云,王妙月.海洋可控源电磁法三维数值模拟[J].石油地球物理勘探,2009,44(3):358-363.Fu Chang-min,Di Qing-yun,Wang Miao-yue.Ma-rine CSEM3D Modeling[J].Oil Geophysical Pros-pecting,2009,44(3):358-363.
[14]Zhdanov M S,Cuma M,Wilson G A,et al.Iterative Electromagnetic Migration for3DInversion of Marine Controlled-Source Electromagnetic Data[J].Geo-physical Prospecting,2011,59:1101-1113.
[15]Andréis D,MacGregor L.Controlled-Source Electro-magnetic Sounding in Shallow Water:Principles and Applications[J].Geophysics,2008,73(1):F21-F32.
[16]Weiss C J.The Fallacy of the“Shallow-Water Prob-lem”in Marine CSEM Exploration[J].Geophysics,2007,72(6):A93-A97.
[17]Wait J R.The Electromagnetic Fields of A Horizon-tal Dipole in the Presence of a Conducting Half-Space[J].Can J Phys,1961,39:1017-1028.
[18]Bannister P R.New Simplified Formulas for ELF Subsurface to Subsurface Propagation[J].IEEE J Ocean Eng,1984,9:154-163.
[19]King R W P,Owens M,Wu T T.Lateral Electro-magnetic Waves[M].New York:Springer-Verlag,1992.
[20]Amundsen L,Lφseth L,Mitten S,et al.Decomposi-tion of Electromagnetic Fields into Upgoing and Downgoing Components[J].Geophysics,2006,71:G211-G223.
[21]Um E S,Alumbaugh D L.On the Physics of the Ma-rine Controlled-Source Electromagnetic Method[J].Geophysics,2007,72(2):WA13-WA26.
[22]Weidelt P.Guided Waves in Marine CSEM[J].Geo-phys J Int,2007,171:153-176.
[23]Lφseth L O,Amundsen L.Removal of Air-Response by Weighting Inline and Broadside CSEM/SBL Data[C]//77th Annual International Meeting.San An-tonio:SEG,2007:529-533.
[24]Lφseth L O,Amundsen L,Jenssen A J K.A Solu-tion to the Airwave-Removal Problem in Shallow-Wa-ter Marine EM[J].Geophysics,2010,75(5):A37-A42.
[25]Hunziker J,Slob E,Mulder W.Effects of the Air-wave in Time-Domain Marine Controlled-Source Elec-tromagnetics[J].Geophysics,2011,76(4):F251-F261.
[26]Constable S C.Method and System for Seafloor Geo-logical Survey Using Vertical Electric Field Measure-ment:U S,WO2003104844[P].2003-12-18.
[27]Holten T,Flekky E G,Singer B,et al.Vertical Source,Vertical Receiver,Electromagnetic Tech-nique for Offshore Hydrocarbon Exploration[J].First Break,2009,27:89-93.
[28]Dell’Aversana P.Improving Interpretation of CSEM in Shallow Water[J].TLE,2007:332-335.
[29]Frenkel M,Davydycheva S.A Modeling Study of Low-Frequency CSEM in Shallow Water[C]//71st Annual International Conference&Exhibition.Am-sterdam:EAGE,2009:075.
[30]Li Y G,Constable S.Transient Electromagnetic in Shallow Water:Insights from1D Modeling[J].Chi-nese J Geophys,2010,53:737-742.
[31]Wait J R,Campbell L L.The Fields of an Electric Dipole in a Semi-Infinite Conducting Medium[J].J Geophys Res,1953,58:21-28.
[32]Wait J R,Campbell L L.The Fields of an Oscillating Magnetic Dipole Immersed in a Semi-Infinite Conduc-ting Medium[J].J Geophys Res,1953,58:167-178.
[33]Weaver J T.The Quasi-Static Field of an Electric Di-pole Embedded in a Two-Layer Conducting Half-Space[J].Can J Phys,1967,45:1971-2002.
[34]Bannister P R.Quasi-Static Fields of Dipole Anten-nas at Earth’s Surface[J].Radio Sci,1966,1:1321-1330.
[35]Bannister P R,Hart W C.Quasi-Static Fields of Di-pole Antennas Below the Earth’s Surface[R].New London:Naval Underwater Systems Center,1968.
[36]Nordskag J,Amundsen L.Asymptotic Airwave Mo-deling for Marine Controlled Source Electromagnetic Surveying[J].Geophysics,2007,72(6):F249-F255.
[37]Yin C.Electromagnetic Induction in a Layered Con-ductor with Arbitrary Anisotropy[D].Braun-schweig:Technical University Braunschweig,1999.
[38]Lu X,Srnka L J,Carazzone J J.Method for Remo-ving Air Wave Effect from Offshore Frequency Do-main Controlled-Source Electromagnetic Data:U S,WO2005/010560[P].2005-02-03.
[39]Ursin B.Review of Elastic and Electromagnetic Wave Propagation in Horizontally Layered Media[J].Geo-physics,1983,48:1063-1081.
[40]Levy S,Oldenburg D,Wang J.Subsurface Imaging Using Magnetotelluric Data[J].Geophysics,1988,53:104-117.
[41]Zhdanov M S,Traynin P,Booker J R.Underground Imaging by Frequency-Domain Electromagnetic Mi-gration[J].Geophysics,1996,61:666-682.
[42]Van den Berg P M,Abubakar A,Habashy T.Re-moving Sea Surface-Related Electromagnetic Fields in Performing an Electromagnetic Survey:U S,WO/2008/054888[P].2008-09-30.
[43]Chen J P,Alumbaugh D L.Three Methods for Miti-gating Airwaves in Shallow Water Marine Controlled-Source Electromagnetic Data[J].Geophysics,2011,76(2):F89-F99.
[44]Maaφ F A,Nguyen A K.Enhanced Subsurface Re-sponse for Marine CSEM Surveying[J].Geophysics,2010,75(3):A7-A10.
[45]Wirianto M,Mulder W A,Slob E C.Exploiting the Airwave for Time-Lapse Reservoir Monitoring with CSEM on Land[J].Geophysics,2011,76(3):A15-A19.
[46]Mittet R.Normalized Amplitude Ratios for Frequen-cy-Domain CSEM in Very Shallow Water[J].First Break,2008,26(11):47-54.
[47]Ziolkowski A,Wright D.Removal of the Airwave in Shallow Marine Transient EM Data[C]//77th Annual International Meeting.San Antonio:SEG,2007:534-538.
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