Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSE...Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSEM. The propagation of the electromagnetic fields from a controlled source in the marine environment was studied with virtual interface method combined with discrete complex image method. Transmitter of finite length current source is approximated by dipole (HED) . A three-layered model is accepted,with sea water as intermediate conductive layer under air and a relatively high resistive seabed as basement,possibly containing a hydrogen layer of higher resistivity. The electromagnetic fields in whole space thus computed show that: (1) the spatial distribution of field component depends on its type; (2) inline Ex component is more sensitive to reservoir layer than that in broadside; (3) The airwave affects marine electromagnetic (MEM) exploration when sea water is relatively shallow; in the case of deep water MEM exploration,the airwave influence could be neglected; and (4) an appropriate frequency should be selected in order to balance the signal strength and electromagnetic induction effect.展开更多
A high-power marine controlled-source electromagnetic transmitter(HP-MCSET)transmits a highfrequency conversion current on the sea floor.Some problems exist when the direct-current to alternating-current(DC-AC)launch ...A high-power marine controlled-source electromagnetic transmitter(HP-MCSET)transmits a highfrequency conversion current on the sea floor.Some problems exist when the direct-current to alternating-current(DC-AC)launch bridge(LB)is used in the marine controlled-source electromagnetic transmitter(MCSET).There is a high voltage peak in the LB when the insulated gate bipolar transistor(IGBT)is turned on and off.In some cases,the voltage stress of the IGBT can be exceeded,which may cause IGBT damage.Because the rise of the current steepness is relatively low and the output voltage has a voltage peak in the LB,a snubber circuit is added to the IGBT to suppress the voltage peak to improve the output current and voltage waveform.The suppression of the voltage peaks is analyzed and compared for several groups of snubber circuits.To meet the performance requirements of the MCSET,the optimal snubber circuit is selected to effectively suppress the voltage peaks at an output current of 1 kA.This method is verified by using a 70 kW MCSET and the experimental waveforms are provided.The simulation of the inductance obstruction load in seawater is necessary to determine the conditions for actual marine environment experiments.展开更多
As an important branch of geophysical exploration method,the electromagnetic method with artificial source has advanced rapidly in the past decade.These methods are classified as airborne electromagnetic method,ground...As an important branch of geophysical exploration method,the electromagnetic method with artificial source has advanced rapidly in the past decade.These methods are classified as airborne electromagnetic method,ground-air electromagnetic method,ground electromagnetic method,and marine electromagnetic method.Over the years,researchers in China have made significant improvement to the fundamental theory,forward modeling and inverse for series of electromagnetic detection methods.Conversely,significant progress was made in the development of corresponding equipment.The researched techniques and their developed equipment have been successfully utilized to detect underground targets as deep as 10 km.However,there is increasing need for deep resources exploration,urban subsurface study,and prediction,monitoring and detection of geological hazards.To meet the increasing need and catch up with the advanced international level of exploration technologies and developed equipment,there is urgent necessity and requirement to continue developing geophysical methods and the corresponding equipment.展开更多
The transient electromagnetic(TEM)method becomes more urgent than ever for marine ex-ploration due to abundant resource reserves and the increasing undersea engineering construction activities,especially in the offsho...The transient electromagnetic(TEM)method becomes more urgent than ever for marine ex-ploration due to abundant resource reserves and the increasing undersea engineering construction activities,especially in the offshore exploration of mineral deposits such as Sanshandao gold mine.However,the re-search and application of TEM method in marine environment are still challenged by many problems.Such contradiction motivates our study on the coincident-loop TEM in seafloor exploration.The TEM response of coincident loops is firstly derived in the integral form,based on the potential functions in Helmholtz equ-ations for a magnetic source locating in the whole-space layered model.The frequency-domain vertical magnetic field is described as the Hankel integral with double first-order Bessel functions of first kind.Se-condly,the time-domain induced voltage is obtained by transforming the frequency-domain response through the cosine transform and then taking the derivative of time.To simultaneously solve the Hankel transform and the cosine transform,a novel algorithm is introduced by adapting the fixed-point quadra-ture and extrapolation via the Shanks transformation.Finally,a typical conductivity model for marine po-lymetallic deposit is designed to investigate the characteristic of TEM response under various conditions.Numerical results demonstrate that existence of conductive seawater causes the TEM response to increase significantly and decay slower.The air-sea reflected electromagnetic waves lead to a significantly large fake negative response(NR)in shallower seawater with depth less than 300 m.Increase in the height of loops will weaken and delay the anomaly response and shorten the observation time-window.The height of configu-ration should be no more than 100 m for shallower targets and 50 m for deeper targets,respectively.The observation time-window should cover 10-1000 ms.Increase in the radius of loops only enhances the TEM response proportionally but hardly improves the relative anomaly.The vertical resolution on the low-resistivity target approximates 20 m for the configuration considered in the study.Decreases in D.C.resistivity and chargeability cause the positive response(PR)to increase significantly and decay more ra-pidly.Meanwhile,the NR is advanced and enlarged significantly and decays slower compared with the PR.The influence of time constant is not monotony and there exists an optimal value for producing the maxi-mum NR.As the frequency parameter increases,the PR is caused to decay more rapidly without magni-tude change and the NR is advanced and decays more rapidly with significant increase in magnitude.The influence of frequency parameter is more pronounced than that of time constant.展开更多
基金Supperted by project of the National Science Foundation of China(No.40874050)
文摘Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSEM. The propagation of the electromagnetic fields from a controlled source in the marine environment was studied with virtual interface method combined with discrete complex image method. Transmitter of finite length current source is approximated by dipole (HED) . A three-layered model is accepted,with sea water as intermediate conductive layer under air and a relatively high resistive seabed as basement,possibly containing a hydrogen layer of higher resistivity. The electromagnetic fields in whole space thus computed show that: (1) the spatial distribution of field component depends on its type; (2) inline Ex component is more sensitive to reservoir layer than that in broadside; (3) The airwave affects marine electromagnetic (MEM) exploration when sea water is relatively shallow; in the case of deep water MEM exploration,the airwave influence could be neglected; and (4) an appropriate frequency should be selected in order to balance the signal strength and electromagnetic induction effect.
基金the National Science and Technology Major Project(No.2016ZX05021-002)the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences(No.XDB06030204)。
文摘A high-power marine controlled-source electromagnetic transmitter(HP-MCSET)transmits a highfrequency conversion current on the sea floor.Some problems exist when the direct-current to alternating-current(DC-AC)launch bridge(LB)is used in the marine controlled-source electromagnetic transmitter(MCSET).There is a high voltage peak in the LB when the insulated gate bipolar transistor(IGBT)is turned on and off.In some cases,the voltage stress of the IGBT can be exceeded,which may cause IGBT damage.Because the rise of the current steepness is relatively low and the output voltage has a voltage peak in the LB,a snubber circuit is added to the IGBT to suppress the voltage peak to improve the output current and voltage waveform.The suppression of the voltage peaks is analyzed and compared for several groups of snubber circuits.To meet the performance requirements of the MCSET,the optimal snubber circuit is selected to effectively suppress the voltage peaks at an output current of 1 kA.This method is verified by using a 70 kW MCSET and the experimental waveforms are provided.The simulation of the inductance obstruction load in seawater is necessary to determine the conditions for actual marine environment experiments.
基金supported by the Beijing Science and Technology Plan(Grant No.Z181100005718001)the National Key R&D Program(Grant No.2017YFC0601204)the National Natural Science Foundation of China(Grant Nos.41874088&41830101)。
文摘As an important branch of geophysical exploration method,the electromagnetic method with artificial source has advanced rapidly in the past decade.These methods are classified as airborne electromagnetic method,ground-air electromagnetic method,ground electromagnetic method,and marine electromagnetic method.Over the years,researchers in China have made significant improvement to the fundamental theory,forward modeling and inverse for series of electromagnetic detection methods.Conversely,significant progress was made in the development of corresponding equipment.The researched techniques and their developed equipment have been successfully utilized to detect underground targets as deep as 10 km.However,there is increasing need for deep resources exploration,urban subsurface study,and prediction,monitoring and detection of geological hazards.To meet the increasing need and catch up with the advanced international level of exploration technologies and developed equipment,there is urgent necessity and requirement to continue developing geophysical methods and the corresponding equipment.
基金This research was supported by the National Key R&D Program of China(No.2018YFC0603806).
文摘The transient electromagnetic(TEM)method becomes more urgent than ever for marine ex-ploration due to abundant resource reserves and the increasing undersea engineering construction activities,especially in the offshore exploration of mineral deposits such as Sanshandao gold mine.However,the re-search and application of TEM method in marine environment are still challenged by many problems.Such contradiction motivates our study on the coincident-loop TEM in seafloor exploration.The TEM response of coincident loops is firstly derived in the integral form,based on the potential functions in Helmholtz equ-ations for a magnetic source locating in the whole-space layered model.The frequency-domain vertical magnetic field is described as the Hankel integral with double first-order Bessel functions of first kind.Se-condly,the time-domain induced voltage is obtained by transforming the frequency-domain response through the cosine transform and then taking the derivative of time.To simultaneously solve the Hankel transform and the cosine transform,a novel algorithm is introduced by adapting the fixed-point quadra-ture and extrapolation via the Shanks transformation.Finally,a typical conductivity model for marine po-lymetallic deposit is designed to investigate the characteristic of TEM response under various conditions.Numerical results demonstrate that existence of conductive seawater causes the TEM response to increase significantly and decay slower.The air-sea reflected electromagnetic waves lead to a significantly large fake negative response(NR)in shallower seawater with depth less than 300 m.Increase in the height of loops will weaken and delay the anomaly response and shorten the observation time-window.The height of configu-ration should be no more than 100 m for shallower targets and 50 m for deeper targets,respectively.The observation time-window should cover 10-1000 ms.Increase in the radius of loops only enhances the TEM response proportionally but hardly improves the relative anomaly.The vertical resolution on the low-resistivity target approximates 20 m for the configuration considered in the study.Decreases in D.C.resistivity and chargeability cause the positive response(PR)to increase significantly and decay more ra-pidly.Meanwhile,the NR is advanced and enlarged significantly and decays slower compared with the PR.The influence of time constant is not monotony and there exists an optimal value for producing the maxi-mum NR.As the frequency parameter increases,the PR is caused to decay more rapidly without magni-tude change and the NR is advanced and decays more rapidly with significant increase in magnitude.The influence of frequency parameter is more pronounced than that of time constant.
