浅海瞬变电磁全波形响应特征及探测能力分析
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摘要
瞬变电磁法在浅海工程勘探等领域受到了越来越多的关注.目前浅海瞬变电磁仍处于应用初期,相关研究少且未有成熟装备问世,有必要研究其探测能力并为观测系统选取最佳观测参数.本文以几种典型发射波形为例,采用褶积算法细致分析了不同发射波形条件下浅海瞬变电磁on-/off-time响应受海底介质电导率、磁导率及发射波形脉宽等参数的影响特征与规律;通过三维正演并设定极限探测深度阈值,进一步分析不同发射波形on-/offtime期间浅海瞬变电磁探测能力及对典型三维目标体的极限探测深度.基于本文研究成果,可为浅海瞬变电磁探测装置设计、观测系统的参数选取及试验参数的选取等提供了一些有价值的理论借鉴.
The transient electromagnetic(TEM)method in shallow sea has received munch attention as an effective geophysical tool in engineering and environment investigation.Since it is still at its infancy,then it is necessary to study its exploration capability and select the best observation parameters for the investigation system.The advantages of using central loop systems at sea are twofold:simplified navigation and simplified operation.This paper investigates the effect and exploration capability of different TEM transmitter waveforms on measuring dBz/dt and Bz response in shallow sea.First,the characteristic of the transmitter pulse shape is calculated by spectrum analysis.The pulse shapes considered include the square,trapezoid,triangular and half-sine shape.Then,using the convolution algorithm,we analyze the influence of seafloor conductivity,permeability,waveform plus width and the on-and off-time dBz/dt and Bzsignals on the exploration capability.Finally,in order to simulate the three-dimensional marine TEM response,the vector finite element method(VFEM)is used to simulate the on-and off-time dBz/dt andBzresponse over a 3 Dconductor which buried in the seafloor,and calculate the exploration depth of different transmitting waveforms,on-and off-time TEM response.The accuracy of our algorithm is checked with previous work.The result shows a good agreement.The following observations are obtained based on numerical tests:1)TEM response in shallow sea has good resolving power to the conductive seafloor,but poor one to the resistive seafloor.2)TEM response in shallow sea increases with the increasing seafloor permeability,Bzresponse is more sensitive to the permeability changes than dBz/dt response,and triangular and half-sine waves are more strongly influenced by the change in seafloor permeability than trapezoid wave.3)Depending on the detected target,the exploration capability and efficiency of shallow sea TEM can be enhanced by choosing appropriate pulse width.4)The on-and off-time Bz response has deeper exploration depth than the dBz/dt response.5)The effect in turn-off time of trapezoid waves on the exploration capability of ontime response is greater than off-time response,both for Bzand dBz/dt response.The presented work provides theoretical basis for both the development of shallow sea TEM and selection of observation and interpretation parameters in the future.
The transient electromagnetic(TEM)method in shallow sea has received munch attention as an effective geophysical tool in engineering and environment investigation.Since it is still at its infancy,then it is necessary to study its exploration capability and select the best observation parameters for the investigation system.The advantages of using central loop systems at sea are twofold:simplified navigation and simplified operation.This paper investigates the effect and exploration capability of different TEM transmitter waveforms on measuring dBz/dt and Bz response in shallow sea.First,the characteristic of the transmitter pulse shape is calculated by spectrum analysis.The pulse shapes considered include the square,trapezoid,triangular and half-sine shape.Then,using the convolution algorithm,we analyze the influence of seafloor conductivity,permeability,waveform plus width and the on-and off-time dBz/dt and Bzsignals on the exploration capability.Finally,in order to simulate the three-dimensional marine TEM response,the vector finite element method(VFEM)is used to simulate the on-and off-time dBz/dt andBzresponse over a 3 Dconductor which buried in the seafloor,and calculate the exploration depth of different transmitting waveforms,on-and off-time TEM response.The accuracy of our algorithm is checked with previous work.The result shows a good agreement.The following observations are obtained based on numerical tests:1)TEM response in shallow sea has good resolving power to the conductive seafloor,but poor one to the resistive seafloor.2)TEM response in shallow sea increases with the increasing seafloor permeability,Bzresponse is more sensitive to the permeability changes than dBz/dt response,and triangular and half-sine waves are more strongly influenced by the change in seafloor permeability than trapezoid wave.3)Depending on the detected target,the exploration capability and efficiency of shallow sea TEM can be enhanced by choosing appropriate pulse width.4)The on-and off-time Bz response has deeper exploration depth than the dBz/dt response.5)The effect in turn-off time of trapezoid waves on the exploration capability of ontime response is greater than off-time response,both for Bzand dBz/dt response.The presented work provides theoretical basis for both the development of shallow sea TEM and selection of observation and interpretation parameters in the future.
引文
Balch S J,Boyko W P,Paterson N R.2003.The AeroTEMairborne electromagnetic system.The Leading Edge,22(6):562-566.
Barsukov P O,Fainberg E B.2014.Transient marine electromagnetics in shallow water:A sensitivity and resolution study of the vertical electric field at short ranges.Geophysics,79(1):E39-E49,doi:10.1190/geo2013-0125.1.
Cheesman S J,Edwards R N,Chave A D.1987.On the theory of sea-floor conductivity mapping using transient electromagnetic systems.Geophysics,52(2):204-217,doi:10.1190/1.1442296.
Chen S D,Lin J,Zhang S.2012.Effect of transmitter current waveform on TEM response.Chinese J.Geophys.(in Chinese),55(2):709-716,doi:10.6038/j.issn.0001-5733.2012.02.035.
Chen T Y,Hodges G,Miles P.2015.MULTIPULSE-high resolution and high power in one TDEM system.Exploration Geophysics,46(1):49-57,doi:10.1071/EG14027.
Constable S.2010.Ten years of marine CSEM for hydrocarbon exploration.Geophysics,75(5):75A67-75A81,doi:10.1190/1.3483451.
Doll W E,Gamey T J,Holladay J S,et al.2010.Results of a highresolution airborne TEM system demonstration for unexploded ordnance detection.Geophysics,75(6):B211-B220,doi:10.1190/1.3505817.
Edwards R N,Chave A D.1986.A transient electric dipole-dipole method for mapping the conductivity of the sea floor.Geophysics,51(4):984-987.
Eidesmo T,Ellingsrud S,MacGregor L M,et al.2002.Sea bed logging(SBL),a new method for remote and direct identification of hydrocarbon filled layers in deepwater areas.First Break,20(3):144-152.
Everett M E,Edwards R N.1993.Transient marine electromagnetics:the 2.5-D forward problem.Geophysical Journal International,113(3):545-561.
Evjen H M.1938.Depth factors and resolving power of electrical measurements.Geophysics,3(2):78-95.
Fan T,Cheng J Y,Wang B L,et al.2016.Imaging method of TEM pseudo wave-field and application of unexploded ordnance detection.Progress in Geophysics(in Chinese),31(5):2326-2332,doi:10.6038/pg20160561.
Fountain D,Smith R,Payne T,et al.2005.A helicopter timedomain EM system applied to mineral exploration:system and data.First Break,23:73-78.
Goto T,Takekawa J,Mikada H,et al.2011.Marine electromagnetic sounding on submarine massive sulphides using remotely operated vehicle(ROV)and autonomous underwater vehicle(AUV).∥Proceedings of the 10th SEGJ International Symposium.Kyoto:Society of Exploration Geophysicists of Japan,1-5.
He J H,Bao L Z.1999.The situation and progress of marine electromagnetic method research.Progress in Geophysics(in Chinese),14(1):7-39.
Huang S,Yu X S,Yan Z J,et al.2014.1-D modeling of marine electromagnetic method for detecting underwater UXO.Scientific Journal of Earth Science,4(2):93-97.
Kerry K.2009.1Dinversion of multicomponent,multifrequency marine CSEM data:Methodology and synthetic studies for resolving thin resistive layers.Geophysics,74(2):F9-F20,doi:10.1190/1.3058434.
Li H,Lin J,Wang Y,et al.2006.Equipment parameters and experiment of sea-floor transient electromagnetic method.Chinese Journal of Radio Science(in Chinese),21(5):659-664.
Li J H,Zhu Z Q,Lu G Y,et al.2013.Study on three-dimensional forward of transient electromagnetic method excited by loop source.Progress in Geophysics(in Chinese),28(2):754-765,doi:10.6038/pg20130224.
Li Y G,Constable S.2010.Transient electromagnetic in shallow water:insights from 1D modeling.Chinese J.Geophys.,53(3):737-742,doi:10.3969/j.issn.0001-5733.2010.03.029.
Liu C S,Lin J.2006.Transient electromagnetic response modeling of magnetic source on seafloor and the analysis of seawater effect.Chinese J.Geophys.(in Chinese),49(6):1891-1898.
Liu G M.1998.Effect of transmitter current waveform on airborne TEM response.Exploration Geophysics,29(1-2):35-41.
Nabighian M N.1987.Electromagnetic Methods in Applied Geophysics:Theory(Volume 1).Tulsa:SEG,217-221.
Nakayama K,Saito A.2014.Development of new marine TDEMsystems for the ocean bottom hydrothermal deposits.∥84th Ann.Internat Mtg.,Soc.Expi.Geophys..Expanded Abstracts,850-854.
Qi Y F,Yin C C,Liu Y H,et al.2017.3Dtime-domain airborne EM full-wave forward modeling based on instantaneous current pulse.Chinese J.Geophys.(in Chinese),60(1):369-382,doi:10.6038/cjg20170131.
Raiche A P,Spies B R.1981.Coincident loop transient electromagnetic master curves for interpretation of two-layer earths.Geophysics,46(1):53-64.
Sattel D.1998.Improving conductivity models using on-time EMdata.Exploration Geophysics,29(3-4):605-608.
Smith R,Annan P.1998.The use of B-field measurements in an airborne time-domain system:Part I:Benefits of B-field versus dB/dt data.Exploration Geophysics,29(1-2):24-29.
Swidinsky A,H9lz S,Jegen M.2012.On mapping seafloor mineral deposits with central loop transient electromagnetics.Geophysics,77(3):E171-E184,doi:10.1190/geo2011-0242.1.
Weiss C J.2007.The fallacy of the“shallow-water problem”in marine CSEM exploration.Geophysics,72(6):A93-A97,doi:10.1190/1.2786868.
Witherly K,Irvine R,Morrison E.2004.The Geotech VTEM time domain helicopter EM system.ASEG Extended Abstracts,2004(1):1-4.
Yin C,Smith R S,Hodges G,et al.2008.Modeling results of onand off-time B and dB/dt for time-domain airborne EM systems.∥Extended Abstracts,70th Annual EAGE Conference and Exhibition.Rome,1-4.
Yin C C,Ren X Y,Liu Y H,et al.2015.Exploration capability of airborne TEM systems for typical targets in the subsurface.Chinese J.Geophys.(in Chinese),58(9):3370-3379,doi:10.6038/cjg20150929.
Zhao Y,Li X,Wang Y P.2015.Full-domain apparent resistivity definition for large-loop TEM.Progress in Geophysics(in Chinese),30(4):1856-1863,doi:10.6038/pg20150446.
Zhao Y,Xu F,Li X,et al.2017.Characteristics of 3D TEMresponse on seafloor with the central loop configuration.Oil Geophysical Prospecting(in Chinese),52(5):1093-1102,doi:10.13810/j.cnki.issn.1000-7210.2017.05.024.
Zhi Q Q.2015.Study on wave field transformation and migration imaging of MTEM data[Master′s thesis](in Chinese).Xi′an:Chang′an University.
Zhou J M,Li X,Qi Z P.2016.Transient electromagnetic response analysis for anisotropic media in shallow water.Oil Geophysical Prospecting(in Chinese),51(4):821-830,doi:10.13810/j.cnki.issn.1000-7210.2016.04.025.
陈曙东,林君,张爽.2012.发射电流波形对瞬变电磁响应的影响.地球物理学报,55(2):709-716,doi:10.6038/j.issn.0001-5733.2012.02.035.
范涛,程建远,王保利等.2016.瞬变电磁虚拟波场成像方法及其对未爆弹探测的试验研究.地球物理学进展,31(5):2326-2332,doi:10.6038/pg20160561.
何继善,鲍力知.1999.海洋电磁法研究的现状和进展.地球物理学进展,14(1):7-39.
黄颂,于新生,阎子衿等.2014.海底未爆物的电磁探测方法仿真研究.地球科学期刊,4(2):93-97.
李慧,林君,王艳等.2006.海底瞬变电磁探测技术的装置参数研究及实验.电波科学学报,21(5):659-664.
李建慧,朱自强,鲁光银等.2013.回线源瞬变电磁法的三维正演研究.地球物理学进展,28(2):754-765,doi:10.6038/pg20130224.
刘长胜,林君.2006.海底表面磁源瞬变响应建模及海水影响分析.地球物理学报,49(6):1891-1898.
齐彦福,殷长春,刘云鹤等.2017.基于瞬时电流脉冲的三维时间域航空电磁全波形正演模拟.地球物理学报,60(1):369-382,doi:10.6038/cjg20170131.
殷长春,任秀艳,刘云鹤等.2015.航空瞬变电磁法对地下典型目标体的探测能力研究.地球物理学报,58(9):3370-3379,doi:10.6038/cjg20150929.
赵越,李貅,王祎鹏.2015.大回线源瞬变电磁全域视电阻率定义.地球物理学进展,30(4):1856-1863,doi:10.6038/pg20150446.
赵越,许枫,李貅等.2017.中心回线海底三维瞬变电磁响应规律分析.石油地球物理勘探,52(5):1093-1102,doi:10.13810/j.cnki.issn.1000-7210.2017.05.024.
智庆全.2015.MTEM波场变换与偏移成像方法研究[硕士论文].西安:长安大学.
周建美,李貅,戚志鹏.2016.浅水域各向异性地层中的瞬变电磁响应分析.石油地球物理勘探,51(4):821-830,doi:10.13810/j.cnki.issn.1000-7210.2016.04.025.
Barsukov P O,Fainberg E B.2014.Transient marine electromagnetics in shallow water:A sensitivity and resolution study of the vertical electric field at short ranges.Geophysics,79(1):E39-E49,doi:10.1190/geo2013-0125.1.
Cheesman S J,Edwards R N,Chave A D.1987.On the theory of sea-floor conductivity mapping using transient electromagnetic systems.Geophysics,52(2):204-217,doi:10.1190/1.1442296.
Chen S D,Lin J,Zhang S.2012.Effect of transmitter current waveform on TEM response.Chinese J.Geophys.(in Chinese),55(2):709-716,doi:10.6038/j.issn.0001-5733.2012.02.035.
Chen T Y,Hodges G,Miles P.2015.MULTIPULSE-high resolution and high power in one TDEM system.Exploration Geophysics,46(1):49-57,doi:10.1071/EG14027.
Constable S.2010.Ten years of marine CSEM for hydrocarbon exploration.Geophysics,75(5):75A67-75A81,doi:10.1190/1.3483451.
Doll W E,Gamey T J,Holladay J S,et al.2010.Results of a highresolution airborne TEM system demonstration for unexploded ordnance detection.Geophysics,75(6):B211-B220,doi:10.1190/1.3505817.
Edwards R N,Chave A D.1986.A transient electric dipole-dipole method for mapping the conductivity of the sea floor.Geophysics,51(4):984-987.
Eidesmo T,Ellingsrud S,MacGregor L M,et al.2002.Sea bed logging(SBL),a new method for remote and direct identification of hydrocarbon filled layers in deepwater areas.First Break,20(3):144-152.
Everett M E,Edwards R N.1993.Transient marine electromagnetics:the 2.5-D forward problem.Geophysical Journal International,113(3):545-561.
Evjen H M.1938.Depth factors and resolving power of electrical measurements.Geophysics,3(2):78-95.
Fan T,Cheng J Y,Wang B L,et al.2016.Imaging method of TEM pseudo wave-field and application of unexploded ordnance detection.Progress in Geophysics(in Chinese),31(5):2326-2332,doi:10.6038/pg20160561.
Fountain D,Smith R,Payne T,et al.2005.A helicopter timedomain EM system applied to mineral exploration:system and data.First Break,23:73-78.
Goto T,Takekawa J,Mikada H,et al.2011.Marine electromagnetic sounding on submarine massive sulphides using remotely operated vehicle(ROV)and autonomous underwater vehicle(AUV).∥Proceedings of the 10th SEGJ International Symposium.Kyoto:Society of Exploration Geophysicists of Japan,1-5.
He J H,Bao L Z.1999.The situation and progress of marine electromagnetic method research.Progress in Geophysics(in Chinese),14(1):7-39.
Huang S,Yu X S,Yan Z J,et al.2014.1-D modeling of marine electromagnetic method for detecting underwater UXO.Scientific Journal of Earth Science,4(2):93-97.
Kerry K.2009.1Dinversion of multicomponent,multifrequency marine CSEM data:Methodology and synthetic studies for resolving thin resistive layers.Geophysics,74(2):F9-F20,doi:10.1190/1.3058434.
Li H,Lin J,Wang Y,et al.2006.Equipment parameters and experiment of sea-floor transient electromagnetic method.Chinese Journal of Radio Science(in Chinese),21(5):659-664.
Li J H,Zhu Z Q,Lu G Y,et al.2013.Study on three-dimensional forward of transient electromagnetic method excited by loop source.Progress in Geophysics(in Chinese),28(2):754-765,doi:10.6038/pg20130224.
Li Y G,Constable S.2010.Transient electromagnetic in shallow water:insights from 1D modeling.Chinese J.Geophys.,53(3):737-742,doi:10.3969/j.issn.0001-5733.2010.03.029.
Liu C S,Lin J.2006.Transient electromagnetic response modeling of magnetic source on seafloor and the analysis of seawater effect.Chinese J.Geophys.(in Chinese),49(6):1891-1898.
Liu G M.1998.Effect of transmitter current waveform on airborne TEM response.Exploration Geophysics,29(1-2):35-41.
Nabighian M N.1987.Electromagnetic Methods in Applied Geophysics:Theory(Volume 1).Tulsa:SEG,217-221.
Nakayama K,Saito A.2014.Development of new marine TDEMsystems for the ocean bottom hydrothermal deposits.∥84th Ann.Internat Mtg.,Soc.Expi.Geophys..Expanded Abstracts,850-854.
Qi Y F,Yin C C,Liu Y H,et al.2017.3Dtime-domain airborne EM full-wave forward modeling based on instantaneous current pulse.Chinese J.Geophys.(in Chinese),60(1):369-382,doi:10.6038/cjg20170131.
Raiche A P,Spies B R.1981.Coincident loop transient electromagnetic master curves for interpretation of two-layer earths.Geophysics,46(1):53-64.
Sattel D.1998.Improving conductivity models using on-time EMdata.Exploration Geophysics,29(3-4):605-608.
Smith R,Annan P.1998.The use of B-field measurements in an airborne time-domain system:Part I:Benefits of B-field versus dB/dt data.Exploration Geophysics,29(1-2):24-29.
Swidinsky A,H9lz S,Jegen M.2012.On mapping seafloor mineral deposits with central loop transient electromagnetics.Geophysics,77(3):E171-E184,doi:10.1190/geo2011-0242.1.
Weiss C J.2007.The fallacy of the“shallow-water problem”in marine CSEM exploration.Geophysics,72(6):A93-A97,doi:10.1190/1.2786868.
Witherly K,Irvine R,Morrison E.2004.The Geotech VTEM time domain helicopter EM system.ASEG Extended Abstracts,2004(1):1-4.
Yin C,Smith R S,Hodges G,et al.2008.Modeling results of onand off-time B and dB/dt for time-domain airborne EM systems.∥Extended Abstracts,70th Annual EAGE Conference and Exhibition.Rome,1-4.
Yin C C,Ren X Y,Liu Y H,et al.2015.Exploration capability of airborne TEM systems for typical targets in the subsurface.Chinese J.Geophys.(in Chinese),58(9):3370-3379,doi:10.6038/cjg20150929.
Zhao Y,Li X,Wang Y P.2015.Full-domain apparent resistivity definition for large-loop TEM.Progress in Geophysics(in Chinese),30(4):1856-1863,doi:10.6038/pg20150446.
Zhao Y,Xu F,Li X,et al.2017.Characteristics of 3D TEMresponse on seafloor with the central loop configuration.Oil Geophysical Prospecting(in Chinese),52(5):1093-1102,doi:10.13810/j.cnki.issn.1000-7210.2017.05.024.
Zhi Q Q.2015.Study on wave field transformation and migration imaging of MTEM data[Master′s thesis](in Chinese).Xi′an:Chang′an University.
Zhou J M,Li X,Qi Z P.2016.Transient electromagnetic response analysis for anisotropic media in shallow water.Oil Geophysical Prospecting(in Chinese),51(4):821-830,doi:10.13810/j.cnki.issn.1000-7210.2016.04.025.
陈曙东,林君,张爽.2012.发射电流波形对瞬变电磁响应的影响.地球物理学报,55(2):709-716,doi:10.6038/j.issn.0001-5733.2012.02.035.
范涛,程建远,王保利等.2016.瞬变电磁虚拟波场成像方法及其对未爆弹探测的试验研究.地球物理学进展,31(5):2326-2332,doi:10.6038/pg20160561.
何继善,鲍力知.1999.海洋电磁法研究的现状和进展.地球物理学进展,14(1):7-39.
黄颂,于新生,阎子衿等.2014.海底未爆物的电磁探测方法仿真研究.地球科学期刊,4(2):93-97.
李慧,林君,王艳等.2006.海底瞬变电磁探测技术的装置参数研究及实验.电波科学学报,21(5):659-664.
李建慧,朱自强,鲁光银等.2013.回线源瞬变电磁法的三维正演研究.地球物理学进展,28(2):754-765,doi:10.6038/pg20130224.
刘长胜,林君.2006.海底表面磁源瞬变响应建模及海水影响分析.地球物理学报,49(6):1891-1898.
齐彦福,殷长春,刘云鹤等.2017.基于瞬时电流脉冲的三维时间域航空电磁全波形正演模拟.地球物理学报,60(1):369-382,doi:10.6038/cjg20170131.
殷长春,任秀艳,刘云鹤等.2015.航空瞬变电磁法对地下典型目标体的探测能力研究.地球物理学报,58(9):3370-3379,doi:10.6038/cjg20150929.
赵越,李貅,王祎鹏.2015.大回线源瞬变电磁全域视电阻率定义.地球物理学进展,30(4):1856-1863,doi:10.6038/pg20150446.
赵越,许枫,李貅等.2017.中心回线海底三维瞬变电磁响应规律分析.石油地球物理勘探,52(5):1093-1102,doi:10.13810/j.cnki.issn.1000-7210.2017.05.024.
智庆全.2015.MTEM波场变换与偏移成像方法研究[硕士论文].西安:长安大学.
周建美,李貅,戚志鹏.2016.浅水域各向异性地层中的瞬变电磁响应分析.石油地球物理勘探,51(4):821-830,doi:10.13810/j.cnki.issn.1000-7210.2016.04.025.