WO2006051298A1 - Source sismique en fond de trou magnetostrictive - Google Patents

Source sismique en fond de trou magnetostrictive Download PDF

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Publication number
WO2006051298A1
WO2006051298A1 PCT/GB2005/004333 GB2005004333W WO2006051298A1 WO 2006051298 A1 WO2006051298 A1 WO 2006051298A1 GB 2005004333 W GB2005004333 W GB 2005004333W WO 2006051298 A1 WO2006051298 A1 WO 2006051298A1
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WO
WIPO (PCT)
Prior art keywords
signal
formation
borehole
transducer
seismic
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Ceased
Application number
PCT/GB2005/004333
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English (en)
Inventor
Stephen Mclaughlin
Anton Ziolkowski
Brendan Michael Walsh
Alistair Brand
Jimmy Dripps
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University of Edinburgh
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University of Edinburgh
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Publication date
Application filed by University of Edinburgh filed Critical University of Edinburgh
Publication of WO2006051298A1 publication Critical patent/WO2006051298A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
    • G01V1/52—Structural details

Definitions

  • the present invention relates to improvements in seismic source devices, and in particular to but not restricted to magnetostrictive sources for use during in borehole investigations of the sub-surface in oil and gas exploration.
  • Seismic sources are used to propagate an acoustic signal into the earth, which is to be subsequently detected at appropriately designed receivers that record the signal.
  • the purpose of seismic source/receiver systems is to determine properties of the earth in the region between the source and receivers. Typically, the characteristic velocity of a rock formation, the acoustic impedance, or other reflection characteristics are investigated. Such investigations reveal information regarding the structure of the earth local to the source and receiver.
  • Seismic investigations can be conducted on a number of scales. In many cases it is desirable to deploy seismic sources and receiver arrays together in a single well to investigate the formation properties near to the wellbore.
  • data may be interpreted to assist and guide drilling of the well. Specifically, a recorded signal that has been reflected back from a particular target can provide early warning of a problematic structure that should not be drilled.
  • a seismic source is driven in a manner that enables a signal with a particular form to be generated and transmitted.
  • An accurate and reproducible source signal facilitates processing of the receiver signal into an interpretable form.
  • Signals may be constructed to have a particular frequency content or amplitude and phase attributes selected for a given task.
  • the ability to resolve sub surface structures at various ranges from the source is a major consideration for designing an appropriate source signal.
  • a common type of seismic source is an electro-mechanical source, which produces a seismic signal from a mechanical impact generated in response to an electrical input signal.
  • electro-mechanical source which produces a seismic signal from a mechanical impact generated in response to an electrical input signal.
  • These sources rely on the impact between components which, in general, is difficult to accurately repeat. For example, each time there is an impact, differing amounts of energy are dissipated as friction. Such unclean impacts make it difficult to generate a well-defined pulse.
  • These sources operate over a limited frequency band, typically up to about 400 Hz. This compromises resolution and the ability to process the data effectively.
  • Piezo-electric sources have been used in sonar applications for looking ahead of the bit whilst drilling.
  • such systems do not transfer energy efficiently to the source and into the earth.
  • a further type of seismic source is a magnetostrictive source, which contains an electric coil/magnet transducer for turning electric input pulses into mechanical pulses.
  • magnetostrictive devices have been developed to generate signals over a wide frequency range.
  • the best known magnetostrictive device is a reaction-mass source developed by Sandia National Laboratories, which was designed for environmental applications. In this source, the transducer displaces a large mass in order to create the seismic signal. As a result, a significant current must be generated in the transducer coil in order to move the mass. This requirement causes difficulties when generating a signal because as the current is switched, a significant back EMF results, which can burn out the transducer coils.
  • a system for use in a borehole in an earth formation comprising: (a) a downhole assembly conveyed in the borehole; (b) a magnetostrictive transducer on the downhole assembly which produces a mechanical displacement of a coupling member when activated by an electrical signal from a source thereof; (c) at least one contact member in contact with a wall of the borehole and hydraulically coupled to the transducer, the at least one contact member producing a seismic signal in the formation in response to the mechanical displacement of the coupling member.
  • the magnetostrictive transducer comprises an alloy of terbium, dysprosium, and iron.
  • the electrical signal may be selected from the group consisting of (i) a pseudo-random binary sequence, and (ii) a swept frequency signal.
  • the system may further comprise a plurality of extension devices which maintain the transducer substantially in a fixed position in the borehole.
  • the hydraulic coupling may be provided by: (i) a master cylinder having an axis substantially parallel to an axis of the borehole, and ( ⁇ ) at least one slave cylinder coupled through an extension device to the at least one contact member, the at least one slave cylinder oriented substantially orthogonal to the master cylinder.
  • the signal may further comprise a pseudo-random binary sequence, and the source of the electrical signal may further comprise a shift register provided with a negative feedback loop.
  • the at least one contact member may further comprise a pair of opposed contact members.
  • the system further comprises a conveyance device which conveys the downhole assembly into the borehole, the conveyance device selected from (i) a wireline, (ii) a slickline, and (iii) a drilling tubular.
  • the system may further comprise a receiver which produces an output responsive to the propagation of the seismic signal through the earth formation.
  • the system further comprises a processor which determines from the output of the receiver and the electrical signal a travel time of the seismic signal from the at least one contact member to the receiver.
  • a method of evaluating an earth formation comprising: (a) conveying a downhole assembly into a borehole in the earth formation; (b) providing an electrical signal to a magnetostrictive transducer in the downhole assembly and producing a mechanical displacement of a coupling member coupled to the transducer; and (c) hydraulically coupling at least one contact member in contact with a wall of the borehole to the coupling member and producing a seismic signal in the formation in response to the mechanical displacement.
  • the step of providing the electrical signal may further comprise using at least one of (i) a pseudo-random binary sequence, and (ii) a swept frequency signal.
  • the method may further comprise using a plurality of extension devices for maintaining the transducer substantially in a fixed position in the borehole.
  • the step of hydraulically coupling the at least one contact member in contact with the wall of the borehole further comprises using a master cylinder and at least one slave cylinder coupled through an extension device to the at least one contact member.
  • the signal may comprise a pseudo-random binary sequence
  • the step of providing the electrical signal may further comprise using a shift register provided with a negative feedback loop.
  • the at least one contact member may further comprise a pair of opposed contact members.
  • the method may further comprise conveying the magnetostrictive transducer into the borehole on one of (i) a wireline, (ii) a slickline, and (iii) a drilling tubular.
  • the method further comprises the step of detecting the propagation of the seismic signal through the earth formation.
  • the method may also comprise determining from the detected signal a travel time of the seismic signal through the formation.
  • a computer readable medium for use with a system for use in a borehole in an earth formation, the system comprising: (a) a downhole assembly conveyed in the borehole; (b) a magnetostrictive transducer on the downhole assembly hydraulically coupled to at lest one contact member in contact with a wall of the borehole; the medium comprising instructions which enable a processor to provide a signal to the magnetostrictive transducer which causes the at least one contact member to produce a seismic signal in the formation.
  • the medium further comprises at least one of (i) a ROM, (ii) an EPROM, (iii) an EAROM, (iv) a flash memory, and (v) an optical disk.
  • a seismic source comprising a magnetostrictive transducer, and coupling means for coupling the transducer to a formation, wherein the coupling means includes a hydraulic coupling arrangement.
  • the seismic source is adapted to be run in and coupled to a borehole.
  • the seismic source is adapted to be run on a drill string.
  • the magnetostrictive transducer comprises an alloy of terbium, dysprosium, and iron.
  • the magnetostrictive transducer is a Terfenol-D TM transducer.
  • Terfenol-D is a trade mark of Etrema Products, Inc of Indiana, USA.
  • the coupling arrangement comprises a hydraulic master cylinder coupled to the transducer.
  • the hydraulic master cylinder is coupled to the transducer on a substantially longitudinal axis of the borehole.
  • the coupling arrangement comprises a plurality of slave cylinders coupled to the master cylinder and the borehole.
  • the coupling arrangement is adapted to transmit a substantially non-directional signal in the formation. More preferably, the coupling arrangement comprises pressure pads adapted to transmit an output signal from the slave cylinders to the formation.
  • the slave cylinders are oriented substantially radially in the borehole.
  • two slave cylinders are provided oriented substantially in the same axis.
  • the coupling means comprises a pair of fixing cylinders adapted to fix the transducer radially within the wellbore.
  • activating means is provided for activating the coupling arrangement by moving it from a first position in which it is free from the borehole to a second position in which it is coupled to the borehole.
  • the fixing means increases the hydraulic pressure in the slave cylinders and the fixing cylinders.
  • the seismic source may be adapted to be driven by a digital binary electronic signal.
  • the digital binary electronic signal may be a pseudo- random binary sequence (PRBS) .
  • PRBS pseudo- random binary sequence
  • the PRBS is provided at low voltages.
  • the PRBS is a maximal length (ML) sequence, providing broadband frequency signal characteristics.
  • the ML PRBS can be generated using a 10-stage negative feedback shift register, having two feedback taps combined into an XOR logic gate and modulo-2 summed.
  • a seismic source comprising a magnetostrictive transducer, and coupling means for coupling the transducer to a formation, wherein the seismic source is adapted to be driven by a pseudo-random binary sequence (PRBS) .
  • PRBS pseudo-random binary sequence
  • the PRBS is provided at low voltages.
  • the PRBS is a maximal length (ML) sequence, providing broadband frequency signal characteristics.
  • ML maximal length
  • the ML PRBS is generated using a 10-stage negative feedback shift register, having two feedback taps combined into an XOR logic gate and modulo-2 summed.
  • a seismic source comprising a transducer and coupling means for coupling the transducer to a formation, wherein the coupling means includes a hydraulic coupling arrangement.
  • the seismic source is adapted to be run in and coupled to a borehole.
  • a seismic signal transmission system comprising; - a seismic source coupled to a formation, - means for driving the seismic source using a pseudo-random binary sequence (PRBS) to cause a signal to propagate in a formation, - means for receiving a signal from the formation.
  • PRBS pseudo-random binary sequence
  • the PRBS is provided at low voltages.
  • the PRBS is a maximal length (ML) sequence, providing broadband frequency signal characteristics.
  • ML maximal length
  • the ML PRBS is generated using an nth stage negative feedback shift register, having two feedback taps combined into an XOR logic gate and modulo-2 summed.
  • the seismic source is adapted to be run in and coupled to a borehole.
  • the seismic source is adapted to be run on a drill string.
  • a method of transmitting an acoustic signal in a formation comprising the steps of; a. providing a seismic source, b. coupling the seismic source to the formation by a hydraulic coupling arrangement, c. driving the seismic source to cause an acoustic signal to be transmitted in the formation.
  • step a. involves running the seismic source on a drill string.
  • the step c. is carried out using a pseudo- random binary sequence (PRBS) .
  • PRBS pseudo- random binary sequence
  • the seismic source is the seismic source of any of the fourth, fifth or sixth aspects of the invention.
  • Figure 1 is a side view line drawing of a downhole magnetostrictive seismic source in accordance with an embodiment of the invention
  • FIG. 2A is a state transition diagram for a Finite State Machine (FSM) in accordance with an embodiment of the invention
  • Figure 2B is a schematic representation of a downhole magnetostrictive seismic signal generation and interpretation system in accordance with an embodiment of the invention
  • Figure 3 is a line graph of a processed output signal in accordance with an embodiment of the present invention.
  • Figure. 4 illustrates the arrangement of source and sensors using the source of the present invention
  • a downhole magnetostrictive seismic source at 1.
  • the source 1 is located within the wellbore 3.
  • the source 1 comprises a master cylinder 5 at an operational end, and, a magnetostrictive transducer 7 is located at an input end.
  • the transducer 7 and the master cylinder 5 are connected along a longitudinal axis by a push rod 9, which displaces relative to the master cylinder 5 in accordance with mechanical displacement generated by the transducer 7.
  • the transducer 7 converts electrical pulses into mechanical motion along the longitudinal axis of the transducer 7.
  • the push rod 9 is attached to the transducer such that an electrical signal in the coil is transferred to a mechanical movement of the push rod 9.
  • the push rod may be referred to as a coupling member.
  • the geometry of the coupling member is not important.
  • the source is a Terfenol-D TM transducer, marketed by Etrema Products, Inc of Indiana, USA.
  • a set of slave cylinders 11 are attached to the master cylinder 5 and are provided with large-area pressure pads 15 that are located against the walls 4 of the well bore 3.
  • a set of fixing cylinders 17 attached to the transducer 7 have a set of pressure pads 19 located against the well bore wall 4.
  • the individual cylinders of the slave cylinders 11 and the fixing cylinders 17 substantially oppose each other and are positioned perpendicularly to the longitudinal axis of the source.
  • the above arrangement provides means for securing and locating the source in the borehole.
  • the slave pistons 11 and fixing pistons 17 displace radially away from the main cylinder 5 and transducer 7 according to forces imposed on them due to the pressure exerted on the walls of the cylinder 5. In turn, this force is transferred to the pressure pads 15 and 19 and is applied against the borehole walls 4.
  • the master cylinder 5 is a hydraulic cylinder containing hydraulic fluid.
  • initial pressurisation is provided manually by a hand operated pump. It will be appreciated, however, that pressure may be supplied in the downhole environment via control line or the like, or utilising wellbore pressure, through a control valve assembly.
  • Pressurising the master cylinder 5 simultaneously attaches the slave cylinders and fixing cylinders via pressure pads 15 and 19. Once the source is attached, the hydraulic link between the fixing cylinder set 17 and the master cylinder 5 is terminated by sealing a valve between them. This removes the possibility of pressure variations occurring in the fixing cylinder set 17 as a result of mechanical displacement of the push rod 9 into the master cylinder 5.
  • Hydraulic attachment of the source to the borehole provides advantages. Because the pressure pads are in contact with the rock formation, the applied source signal has an effective coupling to the formation. This coupling minimizes any source energy trapped within the borehole, thus, reducing the occurrence of tube standing waves and resonances, which are otherwise susceptible to occur.
  • this source arrangement provides a method through which relatively small displacements of the push rod 9 into the cylinder 5 yield the production of significant pressure at the pressure pads 11.
  • this system is considerably lighter than existing magnetostrictive downhole sources/systems, making it easier to deploy.
  • the clamp design and relatively low power requirements for driving the source allows attachment of the source to the tool string deployed in connection with drilling of a well. This prevents any need to remove the tool string prior to carrying out a seismic borehole investigation, for example, for sub-surface structural investigations for use in the direction of the drilling process.
  • the source couples effectively with the well formation and tends not to damage the interior of the borehole, which otherwise would occur for a single pulse electromechanical source.
  • the source signal from the transducer 7 may generally be considered a varying signal around the DC pressure required for attaching the source to the borehole walls 6.
  • FIG. 2A and 2B there is depicted a signal generation and interpretation system depicted at 41 for use with the downhole magnetostrictive seismic source 1 that was described in the above embodiment.
  • the input signal to the source and consequently the signal output into the well formation 49 is derived from a digital negative feedback shift register 43.
  • the purpose of the shift register 43 is to provide the source 1 with a sequence of binary pulses- through electrical connection 44.
  • the shift register 43 is provided with a negative feedback loop 47, which, upon activation, provides a continuous stream of binary pulses until otherwise requested.
  • the binary state of the shift register i.e. the binary values at each flip-flop 46
  • commencement of transmission i.e. the binary values at each flip-flop 46
  • the transfer of binary digits into and out of the shift register is governed by clock pulses provided to the register 43 during transmission.
  • the shift register 43 is configured to provide a maximal length, pseudo-random binary sequence (PRBS) of pulses. This is achieved by putting two binary feedback taps 45 through an XOR logic gate and modulo-2 adding as part of the negative feedback loop 47.
  • PRBS pseudo-random binary sequence
  • This configuration provides a maximal length PRBS of length 2 3 -l. In this case, 7 states are cycled between during transmission.
  • the zero state where all flip- flops have binary value 0 is a locked state where transmissions continue to further 0 states. This is provided by a non-zero initial state upon signal generation of a programmed clock and reset device 47.
  • the provision of a PRBS to the well formation using the source 1 has a number of advantages.
  • the signal transmitted by the source propagates through the rock formation to receiving instruments 50 that record the signal 49.
  • the seismic signal detected at the receivers is correlated with the input signal, which is known to be a PRBS signal, which reveals high correlation where the input and output signals match.
  • the provision of a PRBS signal allows significant processing gain to be achieved as a result of the inherent autocorrelation properties of such a signal. Specifically, upon autocorrelation, the signal-to-noise ratio of the output signal is substantially greater than the signal-to-noise ratio of the input signal.
  • This provides the possibility of a signal being detected and retrieved at the receiver despite being originally transmitted as a sequence of pulses below the ambient noise level.
  • This feature of the PRBS signal used in this embodiment, permits the use of a low-voltage current input to the source transducer.
  • the switching of the electrical current in the transducer coil can take place safely without the risk of coil burnout due to back EMFs upon switching.
  • This mechanism provides for maintaining prolonged use of the source components thus saving maintenance costs.
  • PRBS signal Use of a PRBS signal also provides for transmission of a broadband signal into the earth. This provides significant resolution benefits, with high-frequencies used for detection over short length scales.
  • a chirp signal instead of pulsing the source with a PRBS signal, a chirp signal is used.
  • a chirp pulse that is a linear frequency modulated pulse with a start frequency fs and chirp rate ⁇ is denoted as:
  • a particular advantage of using a chirp signal downhole is that if the frequency band is sufficiently large, the autocorrelation is a unit spike in the time domain. For band limited chirp signals, the autocorrelation is the sync function. Like the PRBS, a chirp signal has relatively low power requirements but is able to get a relatively large amount of energy into the formation.
  • a processor may be used instead of the circuitry illustrated in Figures 2A, 2B.
  • Figure 3 is a graph of the autocorrelation of an output signal with the input signal at 60.
  • the graph reveals a substantial amplitude peak at 62 corresponding to the time at which the signal arrives at the receiver.
  • the autocorrelated signal 60 remains within the ambient noise.
  • the receiver is an accelerometer is located in a granite block away from the magnetostrictive source.
  • VSP Vertical Seismic Profile
  • the drillbit is part of a bottomhole assembly (BHA) conveyed in the borehole on a drilling tubular such as a drillstring or coiled tubing.
  • a downhole source is denoted by 153 and a reference receiver at the surface is denoted by Rl.
  • 155 shows an exemplary raypath for seismic waves originating at the source 153 and received by the receiver Rl.
  • the source 153 is usually in a fixed relation to the drillbit in the bottom hole assembly.
  • a raypath 155' when the BHA (and the source) are at a different position 153' near the bottom of the borehole. Raypaths 155 and 155' are shown as curved. This ray- bending commonly happens due to the fact that the velocity of propagation of seismic waves in the earth generally increases with depth. Also shown in Figure 4 is a reflected ray 161 corresponding to seismic waves that have been produced by the source at 153, reflected by an interface such as 163, and received by the receiver at Rl. For the configuration shown in Figure 4, it is necessary to have the downhole clock on which the source operates and a surface clock where the data are received and/or recorded in synchronization.
  • the source may also be conveyed downhole on a wireline as part of a string of logging tools.
  • the BHA and a one or more logging tools are referred to as a downhole assembly.
  • a processor is used to determine the time of propagation of the seismic waves from the source to the receiver from the received and transmitted signals. For looking ahead of the drillbit, a downhole processor is necessary. For the example shown in Figure 4, a downhole processor would be used for controlling the source and typically a surface processor is used for analyzing the signals.
  • the processing of the data may be accomplished by processor. Implicit in the control and processing of the data is the use of a computer program implemented on a suitable machine readable medium that enables the processor to perform the control and processing.
  • the machine readable medium may include ROMs, EPROMs, EAROMs, Flash Memories and Optical disks.
  • the invention has been described with reference to a logging tool conveyed on a drillstring.
  • the method of the present invention is equally applicable for use with NMR logging tools conveyed on a wireline, slickline or coiled tubing.

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  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • Remote Sensing (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

L'invention concerne une source sismique en fond de trou utilisant un transducteur magnétostrictif (7) couplé hydrauliquement à des éléments de contact (15) touchant la paroi d un trou de sonde. Dans un mode de réalisation, l'invention porte sur un système pour utilisation dans un trou de sonde (3) dans une formation terrestre (6), le système comprenant un ensemble en fond de trou acheminé dans le trou de sonde ; un transducteur magnétostrictif (7) sur l'ensemble en fond de trou qui produit un déplacement mécanique d'un élément de couplage (9) en cas d'activation par un signal électrique provenant d'une source de celui-ci ; au moins un élément de contact (15) touchant une paroi (4) du trou de sonde et couplé hydrauliquement au transducteur, ledit au moins un élément de contact produisant un signal sismique dans la formation en réponse au déplacement mécanique de l'élément de couplage.
PCT/GB2005/004333 2004-11-10 2005-11-10 Source sismique en fond de trou magnetostrictive Ceased WO2006051298A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0424808A GB0424808D0 (en) 2004-11-10 2004-11-10 Improvements to seismic sources
GB0424808.4 2004-11-10

Publications (1)

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WO2006051298A1 true WO2006051298A1 (fr) 2006-05-18

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PCT/GB2005/004333 Ceased WO2006051298A1 (fr) 2004-11-10 2005-11-10 Source sismique en fond de trou magnetostrictive

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WO (1) WO2006051298A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111538090A (zh) * 2020-06-08 2020-08-14 自然资源部第一海洋研究所 稀疏激发宽频震源系统及数据处理方法
CN112485332A (zh) * 2020-11-16 2021-03-12 中国铁建重工集团股份有限公司 一种基于伪随机编码的无损检测系统及无损检测方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4700803A (en) * 1986-09-29 1987-10-20 Halliburton Company Transducer forming compression and shear waves for use in acoustic well logging
US4862990A (en) * 1988-12-30 1989-09-05 Conoco Inc. Downhole seismic sources
EP0397318A2 (fr) * 1989-05-08 1990-11-14 Halliburton Geophysical Services, Inc. Source d'énergie pour l'exploration sismique
FR2667518A1 (fr) * 1990-10-08 1992-04-10 Inst Francais Du Petrole Source vibrante electro-hydraulique utilisable notamment dans des puits.
FR2678390A1 (fr) * 1991-06-27 1992-12-31 Inst Francais Du Petrole Source vibrante electro-hydraulique de puits avec circuits hydrauliques resonants.
US5208787A (en) * 1992-01-07 1993-05-04 Shirley Gerald C Rodent control by sound waves

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4700803A (en) * 1986-09-29 1987-10-20 Halliburton Company Transducer forming compression and shear waves for use in acoustic well logging
US4862990A (en) * 1988-12-30 1989-09-05 Conoco Inc. Downhole seismic sources
EP0397318A2 (fr) * 1989-05-08 1990-11-14 Halliburton Geophysical Services, Inc. Source d'énergie pour l'exploration sismique
FR2667518A1 (fr) * 1990-10-08 1992-04-10 Inst Francais Du Petrole Source vibrante electro-hydraulique utilisable notamment dans des puits.
FR2678390A1 (fr) * 1991-06-27 1992-12-31 Inst Francais Du Petrole Source vibrante electro-hydraulique de puits avec circuits hydrauliques resonants.
US5208787A (en) * 1992-01-07 1993-05-04 Shirley Gerald C Rodent control by sound waves

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111538090A (zh) * 2020-06-08 2020-08-14 自然资源部第一海洋研究所 稀疏激发宽频震源系统及数据处理方法
CN112485332A (zh) * 2020-11-16 2021-03-12 中国铁建重工集团股份有限公司 一种基于伪随机编码的无损检测系统及无损检测方法

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