CN112014892A

CN112014892A - Transient electromagnetic shallow layer full wave exploration and measurement system

Info

Publication number: CN112014892A
Application number: CN201910460631.4A
Authority: CN
Inventors: 沈建国; 王元顺
Original assignee: Tianjin University Marine Technology Research Institute
Current assignee: Tianjin University Marine Technology Research Institute
Priority date: 2019-05-30
Filing date: 2019-05-30
Publication date: 2020-12-01

Abstract

A transient electromagnetic shallow full wave survey measurement system comprising: the device comprises a transmitting module, a receiving coil array, a depth movement control module, a data acquisition and control module, upper computer software and a high-power supply; the transmitting module consists of a transmitting coil and a transmitting circuit; the receiving coil array is composed of 64 receiving coils; the depth movement control module consists of a stepping motor and an optical code wheel; the data acquisition and control module consists of an FPGA control circuit, an ADS1278 acquisition circuit and a data storage circuit; the upper computer software displays the processing data uploaded by the FPGA in real time and converts the data into a data format for storage; the method realizes excitation and collection of transient electromagnetic exploration data aiming at the shallow layer, realizes multiple coverage measurement by changing the excitation position, provides continuous transient electromagnetic measurement waveforms for shallow layer exploration, and improves the measurement efficiency.

Description

Transient electromagnetic shallow layer full wave exploration and measurement system

Technical Field

The invention belongs to the technical field of special instruments for measuring and evaluating resistivity interfaces in surface shallow exploration construction, and particularly relates to a transient electromagnetic shallow full-wave exploration measuring system.

Background

In existing transient electromagnetic surveying techniques, both transmission and reception are at the surface. The transmit circuit response time is always present since the coil current cannot be abruptly changed. In addition, the propagation energy of electromagnetic waves in the ground and space is large, and a large amount of electromagnetic energy can be rapidly transmitted near the transmitting coil to enter the stratum. The two factors cause the ground transient electromagnetic exploration method to have a measurement blind area, and the shallow layer cannot be effectively measured. Although the turn-off time of the transmitting coil is improved and the size of the coil is reduced, the problem of measurement blind areas cannot be overcome in principle.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a transient electromagnetic shallow full-wave exploration and measurement system, wherein a transmitting coil is placed in a stratum through a drill hole, a receiving coil system consisting of a receiving coil array is placed in the drill hole, response waveforms of the transmitting coil and the receiving coil after being separated by a certain distance are directly measured, and continuous acquisition of large data volume is realized by synchronously moving the transmitting coil and the receiving coil up and down in the drill hole. And performing multi-angle omnibearing multiple coverage measurement on the shallow conductivity interface to obtain transient electromagnetic measurement data with few or even no blind areas.

A transient electromagnetic shallow full wave survey measurement system comprising: the device comprises a transmitting module, a receiving coil array, a depth movement control module, a data acquisition and control module, upper computer software and a high-power supply; the transmitting module consists of a transmitting coil and a transmitting circuit, the transmitting circuit is driven by a high-power supply, and the generated periodic square waves are excited by the transmitting coil; the receiving coil array is composed of 64 receiving coils, the 64 receiving coils are divided into 16 groups of receiving coil systems, and each coil is composed of 4 coaxial receiving coils with equal spacing; the depth movement control module consists of a stepping motor and an optical code wheel; the data acquisition and control module consists of an FPGA control circuit, an ADS1278 acquisition circuit and a data storage circuit; and the upper computer software displays the processing data uploaded by the FPGA in real time and converts the data into a data format for storage.

To detect useful information such as conductivity in the formation, a borehole is drilled in the ground to form a 4 by 4 array of boreholes, a borehole is selected in the center region of the array of boreholes, a transmitter coil and a receiver coil array are placed, and a receiver coil array is placed in the other boreholes in the ground.

The high-power supply provides strong current drive for the transmitting circuit, the FPGA control circuit controls the period of the square wave generated by the transmitting circuit and the on-off of the square wave, and after the transmitting circuit receives the transmitting instruction of the FPGA, the high-power thyristor in the transmitting circuit controls the on-off of the circuit to cause the current in the transmitting coil to generate rapid change so as to excite a transient electromagnetic field in the drill hole.

The receiving coil array receives eddy current secondary field response excited by a transient electromagnetic field in a stratum and primary field response excited by a transmitting coil, a total response transient waveform obtained by superposing the primary field response and the secondary field response received by the receiving coil is transmitted to the data acquisition and control module, an ADS1278 data acquisition circuit in the data acquisition and control module converts the total response of an analog quantity into a digital signal and then transmits the digital signal to the FPGA control circuit for data processing, and a processing result is cached in DDR3 of the storage circuit and uploaded to upper computer software for real-time transient waveform display and file storage.

The upper computer software firstly obtains the transient waveform response difference of the adjacent stratum, the transient waveform response difference of the adjacent stratum is in direct proportion to the conductivity difference of the adjacent stratum, and after the coefficient correction is carried out in the upper computer software according to the depth information, the transient waveform response difference of the adjacent stratum is converted into the conductivity difference of the adjacent stratum. The stratum is accurately layered with high resolution, and the difference of the conductivity can be numerically integrated to obtain a resistivity curve of the stratum.

The measuring system measures the electromagnetic response waveform of the drill hole through high-density continuous excitation in the drill hole, realizes non-contact continuous measurement of the resistivity interface of the detected stratum, obtains a large amount of continuous formation resistivity measurement waveforms, and provides abundant original information for exploration of shallow resistivity abnormal bodies. The invention has the following beneficial effects:

1. the influence of a blind area is reduced to the maximum extent by utilizing the drill hole, the excitation and the acquisition of transient electromagnetic exploration data aiming at the shallow layer are realized, the multiple coverage measurement is realized by changing the excitation position, and a continuous transient electromagnetic measurement waveform is provided for the shallow layer exploration;

2. the transient electromagnetic measurement method overcomes the defects that the existing transient electromagnetic measurement has single data and only records the process of response monotone reduction, and the recorded original waveform comprises two processes, one is rapid monotone increase, and the other is slow reduction. Wherein. The fast monotonic increase process contains more formation conductivity information, and the slow decrease process contains less formation information.

3. The ADS1278 is taken as a main acquisition chip, and the data conversion precision is 24 bits; the FPGA is used as a main controller, the ADS1278 is controlled to acquire data by multiple pieces simultaneously, the acquired data are stored in the DDR3 to be cached, the acquired data are uploaded to an upper computer, 64-channel data can be processed at one time, the defect that in the traditional transient electromagnetic exploration technology, due to the fact that probes are few, high-density measurement in all directions cannot be achieved is overcome, and the measured data can be received in all directions by one-time excitation. The measuring efficiency is improved.

Drawings

FIG. 1 is a block diagram of a transient electromagnetic shallow full wave survey measurement system;

FIG. 2 is a schematic diagram showing the distribution of transmitting and receiving probes of a transient electromagnetic shallow full-wave survey measurement system;

FIG. 3 is a diagram of a transmitting waveform of a transient electromagnetic shallow full wave survey measuring system.

In the figure: 1. a transmitting module; 2. an array of receiving coils; 3. a depth movement control module; 4. a data acquisition and control module; 5. upper computer software; 6. a high power supply; 7. an earth formation; 8. drilling; 9. a transmitting coil; 10. a receiving coil system.

Detailed Description

The invention will be further described with reference to the drawings and preferred embodiments, but the scope of the invention is not limited thereto.

A transient electromagnetic shallow full-wave exploration and measurement system is shown in figure 1, a transmitting module 1 is powered by a high-power supply 6 and drives a transmitting circuit to transmit periodic square waves, the period of the transmitted square waves is controlled by a program set in an FPGA (field programmable gate array), the transmitted square wave current can be adjusted from 0A to 100A according to the power range of the high-power supply 6, the voltage range can be adjusted from 0A to 900V, the transmitted square waves are excited by a transmitting coil 9 to enter a stratum, and the waveform diagram is shown in figure 3.

The receiving coil system array 2 consists of 64 receiving coils, the 64 coils are divided into 16 groups of receiving coil systems 10, each group of receiving coil systems 10 consists of 4 receiving coils to form a coaxial equidistant coil system, holes are drilled on the ground to be detected at equal intervals to form 4-by-4 array drilled holes, one drilled hole at the central position of a drilled hole matrix is selected as a transmitting hole, and a transmitting coil 9 and one group of receiving coil systems 10 are placed in the drilled hole matrix; the other bore holes are receiving holes, and a set of receiver coil arrays 10 are placed in each receiving hole, as shown in fig. 2.

The transmitting coils 9 and the 16 receiving coil systems 10 can move up and down in the drill holes 8 under the control of the stepping motor and the optical code wheel of the depth movement control module 3 and the FPGA of the data acquisition and control module 4, and the moving distance and the detection depth can be displayed on the upper computer software 5 in real time. The transmitting coil 9 is excited in the modes of conduction, disconnection, reverse conduction and reverse disconnection to complete the square wave excitation process. The on and off times are adjusted according to the depth of the probe. The deeper the probing, the longer the on and off times. Every time the position is moved once, the transmitting coil 9 performs excitation of a periodic square wave, and all the receiving coils receive a secondary field response induced in the stratum by the excitation waveform and a primary field response of the transmitting coil.

Each acquisition channel of the AD acquisition circuit of the data acquisition and control module 4 is connected to a receiving coil, and the acquisition is started 60 milliseconds before the transmitting circuit controls the first conduction signal of the transmitting coil, so as to acquire the full-wave waveform generated in the whole excitation process. And 8 ADS1278 chips are adopted, each ADS1278 chip simultaneously collects 8-channel signals, the collected data are stored in an external memory DDR3, after the collection of the data is finished in one excitation process, the collection is continued for 4 seconds, and the collection of one time is finished. After the collection is finished, the collected data are communicated with an upper computer through a USB3.0 communication protocol after being processed by the FPGA chip of the data collection and control module 4, and the data are transmitted to the upper computer software 5 for display and disk storage. And moving the depth positions of the transmitting coil 9 and the receiving coil system 10 to perform the next transmitting excitation and data acquisition, processing and storage. And transmitting data acquired when the excitation is carried out at different depths, and storing the data by taking the depth as a mark. And the data is called by taking the depth as the traction.

The invention provides a transient electromagnetic shallow full wave exploration and measurement system, which realizes a synchronous acquisition process of up to 64 paths of transient waveforms, takes depth as synchronization and realizes continuous acquisition of 64 paths of response transient waveforms in the process of moving a transmitting coil.

The shallow transient electromagnetic exploration measuring system of the invention excites transient electromagnetic induction response in a borehole according to an electromagnetic induction principle, measures transient response waveforms in and adjacent to the borehole, is different from the existing transient electromagnetic exploration method, solves the response of a full space as a measuring object, and carries out multiple times of covering measurement on a conductivity interface of a shallow layer by moving a transmitting coil and a receiving coil in the borehole, and data acquired by an acquisition system is measured when the transmitting coil and the receiving coil are continuously moved.

Claims

1. A transient electromagnetic shallow full wave exploration measurement system is characterized in that: the method comprises the following steps: the device comprises a transmitting module, a receiving coil array, a depth movement control module, a data acquisition and control module, upper computer software and a high-power supply; the transmitting module consists of a transmitting coil and a transmitting circuit, the transmitting circuit is driven by a high-power supply, and the generated periodic square waves are excited by the transmitting coil; the receiving coil array is composed of 64 receiving coils, the 64 receiving coils are divided into 16 groups of receiving coil systems, and each coil is composed of 4 coaxial receiving coils with equal spacing; the depth movement control module consists of a stepping motor and an optical code wheel; the data acquisition and control module consists of an FPGA control circuit, an ADS1278 acquisition circuit and a data storage circuit; and the upper computer software displays the processing data uploaded by the FPGA in real time and converts the data into a data format for storage.

2. The transient electromagnetic shallow full wave survey measurement system of claim 1, wherein: the high-power supply provides strong current drive for the transmitting circuit, the FPGA control circuit controls the period of the square wave generated by the transmitting circuit and the on-off of the square wave, and after the transmitting circuit receives the transmitting instruction of the FPGA, the high-power thyristor in the transmitting circuit controls the on-off of the circuit to cause the current in the transmitting coil to generate rapid change so as to excite a transient electromagnetic field in the drill hole.

3. The transient electromagnetic shallow full wave survey measurement system of claim 1, wherein: the receiving coil array receives eddy current secondary field response excited by a transient electromagnetic field in a stratum and primary field response excited by a transmitting coil, a total response transient waveform obtained by superposing the primary field response and the secondary field response received by the receiving coil is transmitted to the data acquisition and control module, an ADS1278 data acquisition circuit in the data acquisition and control module converts the total response of an analog quantity into a digital signal and then transmits the digital signal to the FPGA control circuit for data processing, and a processing result is cached in DDR3 of the storage circuit and uploaded to upper computer software for real-time transient waveform display and file storage.

4. The transient electromagnetic shallow full wave survey measurement system of claim 1, wherein: the upper computer software firstly obtains the transient waveform response difference of the adjacent stratum, the transient waveform response difference of the adjacent stratum is in direct proportion to the conductivity difference of the adjacent stratum, and the transient waveform response difference of the adjacent stratum is converted into the conductivity difference of the adjacent stratum after coefficient correction is carried out in the upper computer software according to depth information; the stratum is accurately layered with high resolution, and the difference of the conductivity can be numerically integrated to obtain a resistivity curve of the stratum.