基于场延拓的海洋可控源电磁正演模拟及各向异性特征识别
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摘要
海洋可控源电磁法近年来被广泛应用于海洋油气勘探之中,凭借对高阻含油储层的有效识别大大降低干井率,节约钻探成本。受沉积环境的影响,海底地层常常表现出宏观各向异性,而对海洋各向异性模拟算法进行研究可以更有效地进行海洋电磁数据解释。本文从频率域麦克斯韦方程出发,基于标量势分解理论,通过标量势函数与场的连续性条件,在波数域中将电磁场分别向海底深部和海水中延拓,并在海底耦合到发射源上完成电磁场的求解,进而利用汉克尔变换得到了空间域电磁场。通过对海底介质一维各向异性模型电磁响应特征的分析研究发现,覆盖层各向异性对电磁响应有明显的影响;然而,海底高阻层仅垂向电阻率和厚度对海洋电磁响应产生明显影响。通过极性图的方式可以对海底介质各向异性特征进行有效识别。
Marine controlled-source electromagnetic(MCSEM)has been widely used in offshore hydrocarbon exploration in recent years.Huge drilling cost has been saved because of its high sensitivity to resistive oil reservoirs.The ocean sedimentary environment creates strong stratification and anisotropy in submarine media.Thus,the modeling for MCSEM needs to be made for anisotropic media.In this study,we solved the problem of electromagnetic(EM)field in wavenumber domain by introducing two scalar potentials that are continued upwards and downwards based on the continuation conditions of EM field and coupled to transmitting source at the location of transmitting dipole.The EM field in the space domain was calculated by using Hankel Transform.Through the analysis of anisotropic characteristics,we found that the anisotropy has a great influence on the responses of MCSEM,and only the vertical resistivity and the thickness have an influence on the responses of MCSEM for the resistive reservoir.We set up aprocedure to distinguish the earth's anisotropy from the polar plots of marine apparent resistivity.This study lays a foundation for the inversion and interpretation of marine EM data.
Marine controlled-source electromagnetic(MCSEM)has been widely used in offshore hydrocarbon exploration in recent years.Huge drilling cost has been saved because of its high sensitivity to resistive oil reservoirs.The ocean sedimentary environment creates strong stratification and anisotropy in submarine media.Thus,the modeling for MCSEM needs to be made for anisotropic media.In this study,we solved the problem of electromagnetic(EM)field in wavenumber domain by introducing two scalar potentials that are continued upwards and downwards based on the continuation conditions of EM field and coupled to transmitting source at the location of transmitting dipole.The EM field in the space domain was calculated by using Hankel Transform.Through the analysis of anisotropic characteristics,we found that the anisotropy has a great influence on the responses of MCSEM,and only the vertical resistivity and the thickness have an influence on the responses of MCSEM for the resistive reservoir.We set up aprocedure to distinguish the earth's anisotropy from the polar plots of marine apparent resistivity.This study lays a foundation for the inversion and interpretation of marine EM data.
引文
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[17]殷长春,贲放,刘云鹤,等.三维任意各向异性介质中海洋可控源电磁法正演研究[J].地球物理学报,2014,57(12):4110-4122.Yin Changchun,Ben Fang,Liu Yunhe,et al.MCSEM3D Modeling of Arbitrarily Anisotropy Media[J].Chinese Journal of Geophysics,2014,57(12):4110-4122.
[18]贲放,刘云鹤,黄威,等.各向异性介质中的浅海海洋可控源电磁响应特征[J].吉林大学学报(地球科学版),2016,46(2):581-593.Ben Fang,Liu Yunhe,Huang Wei,et al.MCSEMResponse for Anisotropic Media in Shallow Water[J].Journal of Jilin University(Earth Science Edition),2016,46(2):581-593.
[19]Yin C.Geoelectrical Inversion for a One-Dimensional Anisotropic Model and Inherent Non-Uniqueness[J].Geophysical Journal International,2000,140(1):11-23.
[20]Yin C,Maurer H M.Electromagnetic Induction in a Layered Earth with Arbitrary Anisotropy[J].Geophysics,2001,66(5):1405-1416.
[21]Bronstein I N,Semendjajew K.Taschenbuch der Mathematik[M].Leipzig:Teubner Verlagsgesellschaft and Nauka-Verlag,1979.
[22]Yin C,Zhang P,Cai J.Forward Modeling of Marine DC Resistivity Method for a Layered Anisotropic Earth[J].Applied Geophysics,2016,13(2):279-287.
[23]Li X,Pedersen L B.The Electromagnetic Response of an Azimuthally Anisotropic Half-Space[J].Geophy-sics,1991,56(9):1462-1473.
[24]Yin C,Hodges G.Identification of Electrical Anisotropy from Helicopter EM Data[C]//SAGEEP2003:Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems.San Antonio:[s.n.],2003:419-431.
[2]Bannister P R.Determination of the Electrical Conduc-tivity of the Sea Bed in Shallow Waters[J].Geophysics,1968,33(6):995-1003.
[3]Cox C.Electromagnetic Induction in the Oceans and Inferences on the Constitution of the Earth[J].Geophysical Surveys,1980,4:137-156.
[4]李桐林,林君,刘福春,等.国内外海洋大地电磁测深的发展综述[J].国外地质勘探技术,1998,4:1-10.Li Tonglin,Lin Jun,Liu Fuchun,et al.Review on Marine Magnetotellric Techolonogy and Developments[J].Foreign Geoexploration Techolonogy,1998,4:1-10.
[5]Eidesmo T,Ellingsrud S,Macgregor L,et al.Sea Bed Logging(SBL),a New Method for Remote and Direct Identification of Hydrocarbon Filled Layers in Deepwater Areas[J].First Break,2002,20(3):144-152.
[6]Constable S,Weiss C J.Mapping Thin Resistors and Hydrocarbons with Marine EM Methods:Insights from 1D Modeling[J].Geophysics,2006,71(2):G73-G51.
[7]Zhao L X,Geng J H,Zhang S Y.et al.1-D Controlled Source Electromagnetic Forward Modeling for Marine Gas Hydrates Studies[J].Applied Geophysics,2008,5(2):121-126.
[8]Key K.1D Inversion of Multicomponent,Multifrequency Marine CSEM Data:Methodology and Synthetic Studies for Resolving Thin Resistive Layers[J].Geophysics,2009,74(2):F9-F20.
[9]Silva Crepaldi J L,Pereira Buonora M P,Figueiredo I.Fast Marine CSEM Inversion in the CMP Domain Using Analytical Derivatives[J].Geophysics,2011,76(5):F303-F313.
[10]Streich R,Becken M.Electromagnetic Fields Generated by Finite-Length Wire Sources:Comparison with Point Dipole Solutions[J].Geophysical Prospecting,2011,59(2):361-374.
[11]Everett M E,Constable S.Electric Dipole Fields over an Anisotropic Seafloor:Theory and Application to the Structure of 40Ma Pacific Ocean Lithosphere[J].Geophysical Journal International,1999,136(1):41-56.
[12]Yin C.MMT Forward Modeling for a Layered Earth with Arbitrary Anisotropy[J].Geophysics,2006,71(3):G115-G128.
[13]Lseth L O,Ursin B.Electromagnetic Fields in Planarly Layered Anisotropic Media[J].Geophysical Journal International,2007,170(1):44-80.
[14]Kong F N,Johnstad S E,Rosten T,et al.A 2.5DFinite-Element-Modeling Difference Method for Marine CSEM Modeling in Stratifief Anisotropic Media[J].Geophysics,2008,73(1):F9-F19.
[15]Newman G A,CommerM,Carazzone J J.Imaging CSEM Data in the Presence of Electrical Anisotropy[J].Geophysics,2010,75(2):F51-F61.
[16]刘云鹤,殷长春,翁爱华,等.海洋可控源电磁法发射源姿态影响研究[J].地球物理学报,2012,55(8):2757-2768.Liu Yunhe,Yin Changchun,Weng Aihua,et al.Attitude Effect for Marine CSEM System[J].Chinese Journal of Geophysics,2012,55(8),2757-2768.
[17]殷长春,贲放,刘云鹤,等.三维任意各向异性介质中海洋可控源电磁法正演研究[J].地球物理学报,2014,57(12):4110-4122.Yin Changchun,Ben Fang,Liu Yunhe,et al.MCSEM3D Modeling of Arbitrarily Anisotropy Media[J].Chinese Journal of Geophysics,2014,57(12):4110-4122.
[18]贲放,刘云鹤,黄威,等.各向异性介质中的浅海海洋可控源电磁响应特征[J].吉林大学学报(地球科学版),2016,46(2):581-593.Ben Fang,Liu Yunhe,Huang Wei,et al.MCSEMResponse for Anisotropic Media in Shallow Water[J].Journal of Jilin University(Earth Science Edition),2016,46(2):581-593.
[19]Yin C.Geoelectrical Inversion for a One-Dimensional Anisotropic Model and Inherent Non-Uniqueness[J].Geophysical Journal International,2000,140(1):11-23.
[20]Yin C,Maurer H M.Electromagnetic Induction in a Layered Earth with Arbitrary Anisotropy[J].Geophysics,2001,66(5):1405-1416.
[21]Bronstein I N,Semendjajew K.Taschenbuch der Mathematik[M].Leipzig:Teubner Verlagsgesellschaft and Nauka-Verlag,1979.
[22]Yin C,Zhang P,Cai J.Forward Modeling of Marine DC Resistivity Method for a Layered Anisotropic Earth[J].Applied Geophysics,2016,13(2):279-287.
[23]Li X,Pedersen L B.The Electromagnetic Response of an Azimuthally Anisotropic Half-Space[J].Geophy-sics,1991,56(9):1462-1473.
[24]Yin C,Hodges G.Identification of Electrical Anisotropy from Helicopter EM Data[C]//SAGEEP2003:Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems.San Antonio:[s.n.],2003:419-431.