浅水域可控源海洋电磁测量中空气波的渐近表达与波场分离方法

doi:10.13278/j.cnki.jjuese.201501302

摘要/Abstract

摘要：

可控源海洋电磁(MCSEM)勘探中空气波对海底电磁响应的影响已为业界所重视, 它是由水平电偶极子源发射的电磁信号沿空气-海水界面传播与来自海底地层的有效信号相互作用产生的。在浅水域勘探时, 空气波淹没来自地层的有效信号, 使浅水域MCSEM实现油气层识别产生困难。基于层状介质模型, 采用电磁场的模式分解理论导出了半空间电阻率模型的空气波表达式, 利用该式将空气波在海水层的传播近似用海水-空气界面与海底地层之间的多次鸣震表达。结合源和接收器两边电磁场的传播特征, 导出了有限水深时空气波近似关系, 用于近似模拟空气波响应。为了对比不同方法压制空气波的效果, 基于上行波场和下行波场的分解方法, 获得了含油气高阻储层上上行波的异常幅度增大数倍的结果, 显示了波场分解方法压制空气波的良好效果。最后, 利用不含油气层的背景模型和含油气储层模型电磁响应的数值模拟结果, 比较空气波渐近表达和波场分离2种空气波压制方法可知:对于水平层状模型后者效果更好;前者可适用于崎岖海底地层的数据处理, 后者只适用于水平海底地层。

关键词: 浅水域, 海洋可控源电磁勘探, 鸣震近似, 波场分离, 空气波压制

Abstract:

In marine controlled-source electromagnetic (MCSEM) exploration, the influence on the EM response of the airwave has been paid great attention by the industry and the air wave is one kind of EM signal from the horizontal electric dipole (HED) source that is reflected from or travels along the air-sea interface and return back to receivers. In shallow water domains, the airwave dominates over the effective signal from seabed sediments, and makes it very difficult to identify the hydrocarbon reservoirs. On the basis of the layer model, we have derived airwave expression of half space resistivity model by using the mode decomposition theory of the EM field and the air wave in the sea water layer is approximately expressed as a series of wave reverberations that travel down and backward between the sea surface and the seabed. According to the propagations of EM field near sources and receivers, we have obtained airwave expression of a finite water layer. In order to compare the effectiveness of the various air wave mitigation methods, we have adopted the decomposition method of EM fields into upgoing and downgoing components, and have acuired larger anomaly of several times than that of the raw EM field above the resistive formation, and indicated the favorable effect of airwave attenuation by using of wave separation. Finally, simulation results of electromagnetic responses from different background and reservoir models have been used to check the effectiveness and adaptability of the two air wave mitigation methods of wave reverberations approximation and wave field decomposition, numerical results show that for model of horizontal layers, the latter is more effective, however, the former is applicable to rugged sea floor formation and the latter only fits for horizontal layers.

Key words: shallower water domain, marine controlled-source electromagnetic exploration, wave reverberations approximation, air wave separation, air wave mitigation

中图分类号:

P631.3

沈金松, 汪轩, 魏帅帅, 李曼. 浅水域可控源海洋电磁测量中空气波的渐近表达与波场分离方法[J]. 吉林大学学报(地球科学版), 2015, 45(1): 282-292.

Shen Jinsong, Wang Xuan, Wei Shuaishuai, Li Man. Methods of Air Wave Approximation and Decomposition for Marine Controlled Source Electromagnetic Measurements in Shallower Water Domain[J]. Journal of Jilin University(Earth Science Edition), 2015, 45(1): 282-292.

参考文献

[1] Constable S, Weiss C J. Mapping Thin Resistors and Hydrocarbons with Marine EM Methods:Insights from 1D Modeling[J]. Geophysics, 2006, 71(2):43-51.

[2] Eidesmo T, Ellingsrud S, MacGregor L M, 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.

[3] Ellingsrud S, Eidesmo T, Johansen S, et al. Remote Sensing of Hydrocarbon Layers by Sea Bed Logging-SBL:Results from a Cruise Offshore Angola[J]. The Leading Edge, 2002, 21(10):972-982.

[4] MacGregor L M, Thomkins M, Andreis D. Electromagnetic Surveying for Hydrocarbon Reservoirs:U K, 20050077902[P]. 2005-04-14.

[5] Um E S, Alumbaugh D L. On the Physics of the Marine Controlled-Source Electromagnetic Method[J]. Geophysics, 2007, 72(2):13-26.

[6] Chave A D, Constable S C, Edwards R N. Electrical Exploration Methods for the Seafloor[C]//Nabighian M N.Electromagnetic Methods in Applied Geophy-sics. Tulsa:Society of Exploration Geophysicists, 1991:931-966.

[7] Chen J, Alumbaugh D L. Three Methods for Mitigating Airwaves in Shallow Water Marine Controlled-Source Electromagnetic Data[J]. Geophysics, 2011, 76(2):89-99.

[8] Amundsen L, Løseth L, Mittet R, et al. Decomposition of Electromagnetic Fields into Up Going and Down Going Components[J].Geophysics, 2006, 71(5):211-223.

[9] Constable S. Ten Years of Marine CSEM for Hydrocarbon Exploration[J]. Geophysics, 2010, 75(5):7567-7581.

[10] Maaø F A, Nguyen A K. Enhanced Subsurface Response for Marine CSEM Surveying[J]. Geophysics, 2010, 75(3):7-10.

[11] Chave A D, Cox C S. Controlled Electromagnetic Sources for Measuring Electrical Conductivity Beneath the Oceans:1:Forward Problem and Model Study[J]. Journal of Geophysical Research, 1982, 87(B7):5327-5338.

[12] Wait J R. The Electromagnetic Fields of a Horizontal Dipole in the Presence of a Conducting Half-Space[J]. Canadian Journal of Physics, 1961, 39(7):1017-1027.

[13] Baàos A. Dipole Radiation in the Presence of a Conducting Half-Space[M]. Oxford:Pergamon Press Inc, 1966.

[14] Bannister P R. New Simplified Formulas for ELF Sub-surface-to-Subsurface Propagation[J]. IEEE Journal of Oceanic Engineering, 1984, 9(3):154-163.

[15] King R W P, Owens M, Wu T T. Lateral Electromagnetic Waves:Theory and Applications to Communications, Geophysical Exploration, and Remote Sensing[M]. Newyork:Springer-Verlag Inc, 1992.

[16] Løseth L O, Amundsen L, Jenssen A J K. A Solution to the Airwave-Removal Problem in Shallow-Water Marine EM[J]. Geophysics, 2010, 75(5):37-42.

[17] Ziolkowski A, Wright D. Removal of the Airwave in Shallow Marine Transient EM Data[C]//77th Annual International Meeting. San Antonio:Society of Exploration Geophysicists, 2007:534-538.

[18] Lu X, Srnka L J, Carazzone J J. Method for Removing Air Wave Effect from Offshore Frequency Domain Controlled-Source Electromagnetic Data:U S, O2005/010 560A1[P].2005-10-20.

[19] 殷长春, 刘云鹤, 翁爱华, 等, 海洋可控源电磁法空气波研究现状及展望[J]. 吉林大学学报:地球科学版, 2012, 42(5), 1506-1520. Yin Changchun, Liu Yunhe, Weng Aihua, et al. Research on Marine Controlled Source Electromagnetic Method Airwave[J]. Journal of Jilin University:Earth Science Edition, 2012, 42(5):1506-1520.

[20] 沈金松, 詹林森, 王鹏飞, 等.可控源海洋电磁勘探中空气波影响的理论分析和数值模拟[J]. 地球物理学报, 2012, 55(7):2473-2488. Shen Jinsong, Zhan Linsen, Wang Pengfei, et al. Theoretic Analysis and the Numerical Simulation of the Effects of the Air Wave Interaction on the Marine Controlled Source Electromagnetic Exploration[J]. Chinese Journal of Geophysics, 2012, 55(7):2473-2488.

[21] 刘长胜, 林君. 海底表面磁源瞬变响应建模及海水影响分析[J]. 地球物理学报, 2006, 49(6):1891-1898. Liu Changsheng, Lin Jun. Transient Electromagnetic Response Modeling of Magnetic Source on Seafloor and the Analysis of Seawater Effect[J]. Chinese Journal of Geophysics, 2006, 49(6):1891-1898.

[22] Nordskag J I, Amundsen L, Ursin B. Decomposition of Marine Electromagnetic Fields into TE and TM Modes for Enhanced Interpretation[C]//EGM International Workshop.[S.l]:EGM, 2007.

[23] Ward S H, Hohmann G W. Electromagnetic Theory for Geophysical Applications[C]//Ward H S, Hohmann W G. Electromagnetic Methods in Applied Geophysics.[S.l]:SEG, 1988:131-311.

[24] Weiss C J. The Fallacy of the Shallow-Water Problem in Marine CSEM Exploration[J]. Geophysics, 2007, 72(6):93-97.

[25] Løseth L O, Pedersen H M, Schaug-Pettersen T, et al. A Scaled Experiment for the Verification of the Seabed Logging Method[J]. Journal of Applied Geophysics, 2007, 64(3/4):47-55.

[26] Andréis D, MacGregor L. Controlled-Source Electromagnetic Sounding in Shallow Water:Principles and Applications[J]. Geophysics, 2008, 73(1):21-32.

[27] Ziolkowski A. Developments in the Transient Electromagnetic Method[J]. First Break, 2007, 25(6):99-106.

[28] Mittet R. Normalized Amplitude Ratios for Frequency-Domain CSEM in Very Shallow Water[J]. First Break, 2008, 26(11):47-54.

[29] Wapenaar K, Slob E, Snieder R. Seismic and Electromagnetic Controlled-Source Interferometry in Dissipative Media[J]. Geophysical Prospecting, 2008, 56(3):419-434.

Metrics

Viewed

Full text

Abstract

Cited

Shared

Discussed