CN1936621A - Nuclear magnetic resonance and transient electromagnetic combined instrument and method - Google Patents

Abstract

The invention discloses a geophysical exploration equipment and method, which is a combined nuclear magnetic resonance and transient electromagnetic instrument and a method thereof which combine nuclear magnetic resonance and transient electromagnetic into one. First of all, select the combined instrument in the transient electromagnetic working mode, lay the transmitting coil and receiving coil on the measuring line, and measure each measuring point in the measuring area. After the measurement is completed, conduct preliminary processing on the transient electromagnetic data. Find the low-resistivity point, and calibrate the abnormal low-resistivity measurement point; then switch the coupler to the NMR working mode, and lay the transmitting coil around the calibrated abnormal measurement point for NMR measurement work, in order to The measured data or graphics are compared with the abnormal resistivity measured by transient electromagnetic to judge the authenticity of the abnormal target layer of resistivity measured by transient electromagnetic. Using one set of equipment to realize the functions of the two instruments reduces equipment investment, brings into play the respective advantages of the two instruments, and improves detection efficiency and accuracy.

Description

Nuclear Magnetic Resonance and Transient Electromagnetic Instrument and Its Method

technical field

The invention relates to a geophysical prospecting device and method, in particular to a geophysical prospecting device and method combining nuclear magnetic resonance and transient electromagnetics.

Background technique

NMR method (Surface Nuclear Magnetic Resonance Method, referred to as SNMR method), transient electromagnetic method (Transient Electromagnetic Method, referred to as TEM).

US6177794 discloses a new technology for finding underground liquid minerals with nuclear magnetic resonance phenomenon by using macroscopically manifested nuclear magnetic resonance phenomenon, using a group of phase-controllable receiving antenna arrays and receiving antennas in wells to more accurately measure the presence of underground liquid minerals. The liquid of nuclear magnetic resonance phenomenon, this method uses the coil combination on the ground and underground to receive signals at the same time, which is used to receive nuclear magnetic resonance signals well, and can realize the detection of mineral resources such as underground oil and water. CN01278229 discloses a nuclear magnetic resonance underground water layer detector, including a signal detector, characterized in that an input end of the signal detector is connected to a first switch, and the number end of the first switch is connected in series with a variable speed resistor. The other end of the variable speed resistor is connected in series with the second and third switches, the other end of the second switch is connected in series with a current limiting resistor, and a rectifier and a generator are connected in series in sequence, and the other end of the generator is connected with the signal detector The other end is connected, wherein a first capacitor is connected between the second and third switches, the other end of the first capacitor is connected to the other end of the signal detector, a coil is connected between the first switch and the variable speed resistor, The other end of the coil is connected with the other end of the signal detector, and there is a capacitor between the two ends of the signal detector. The invention applies the nuclear magnetic resonance method to the detection of underground water layers, and designs a nuclear magnetic resonance detection instrument suitable for finding water. The nuclear magnetic resonance instrument and its method of the above-mentioned invention have high measurement accuracy and accurate single-point measurement, but they all have a common deficiency, that is, it takes a long time to measure each point and consumes a lot of money, and it is difficult to realize online measurement or Surface measurement.

US7053622 discloses a transient electromagnetic detection device for measuring underground information and imaging. This method uses a series of distributed recorders on the ground to record the attenuation of electromagnetic signals by emitting an excitation field, so as to detect underground information. Simultaneous measurement of points can correct the drift generated by the recorded data of each point, improve the detection accuracy and sensitivity, and can be used for groundwater detection. CN88221167 discloses a MEMS prospecting device, which is composed of a curve simulation circuit, a floating-point amplifier circuit, a main amplifier logic control circuit, an analog-to-digital converter and a microcomputer. The method has high precision, automatic data collection and processing, and fast speed. It is suitable for induced polarization method, transient electromagnetic method, various DC resistivity methods, natural electric field method and other electrical exploration methods of ground power supply and coil power supply. CN01257200 discloses a method for generating a high-power power supply in the field. The method converts a DC low-voltage power supply into a low-voltage and high-frequency AC current through an oscillator. The low-voltage and high-frequency current is boosted to form a high-voltage and high-frequency AC current. The high-frequency AC current is rectified to form a high-voltage DC power supply as a storage capacitor power supply, and the storage capacitor power supply is controlled by an electronic switch to supply power to the power supply circuit. The advantage of this utility model is that it can obtain a large instantaneous current, but the average power consumption of the power supply is not large. Through the combination of multiple charging and discharging capacitors, the effect of superimposing multiple waveforms can be achieved, thereby increasing the exploration depth. In the practice of finding water, the detection sensitivity of the instrument can be improved. The transient electromagnetic instrument and method of the above invention can directly obtain the resistivity value of a certain underground layer conveniently and quickly, and the test cost is low, but the accuracy of the target layer is not as good as that of the nuclear magnetic resonance method, and low resistivity values often occur. The place is not necessarily the target layer. For example, in the work of finding water, it often happens that low-resistivity areas are not necessarily the best areas for water storage, or even have no water, which requires other subsidy means and methods to be further determined. If the transient electromagnetic field is first used for surface measurement to find out the low resistivity anomaly area, and then the nuclear magnetic resonance is used for accurate positioning, the accuracy of finding the target layer will be greatly improved. However, it is too much investment to use two devices, and a lot of repeated work is required during the measurement, which not only wastes money, but also wastes manpower and time.

Contents of the invention

The purpose of the present invention is to address the shortcomings of the above-mentioned prior art, to provide a combined nuclear magnetic resonance and transient electromagnetic instrument and a method thereof that can take advantage of their respective advantages.

The purpose of the present invention is achieved in the following manner:

The computer 1 is connected to the main control unit 2 through a serial port or USB port, the emission control unit 3 is connected to the high-power power supply 4 through the data bus, connected to the H-bridge circuit 5 through the interactive signal line, and connected to the switching switch 6 through the control line. The power supply 4 is connected to the switch 6 via the H bridge 5, and the main control unit 2 is connected to the transmitting control unit 3 and the receiving control unit 15 through the SPI serial interface;

——Transient electromagnetic working mode: the output end of the H-bridge 5 is directly connected to the two ends of the transmitting coil 8 to generate a transient electromagnetic signal, and the receiving coil 12 sends the transient electromagnetic signal to the broadband amplification unit 13 for signal conditioning and then sends it to signal acquisition Unit 14 and receiving control unit 15;

——NMR working mode: the output ends of the two bridge arms of the H-bridge 5 are connected to the matching capacitor 7 and the transmitting coil 8, and the frequency selection amplifying unit 11 is connected to the transmitting coil 8 through the relay 10, and the signal is sent to the signal acquisition Unit 14 and reception control unit 15 , two diodes 9 are connected in reverse to themselves, and are connected to resonant capacitor 7 .

The coupled nuclear magnetic resonance and transient electromagnetic apparatus and its method work according to the following method steps:

a. Select the combined nuclear magnetic resonance and transient electromagnetic instrument in the transient electromagnetic working mode, adopt the method of large loop, lay the transmitting coil 8 and place the receiving coil 12 around each measuring point, and use the transient electromagnetic method to detect fast The characteristics of each measuring point in the survey area are measured. After the measurement is completed, the transient electromagnetic data is initially processed to find out the low resistivity point in the survey area and calibrate the abnormal measuring point with low resistivity. ;

b. Switch the combined nuclear magnetic resonance and transient electromagnetic instrument to the nuclear magnetic resonance working mode, and lay the transmitting coil 8 centered on the calibrated abnormal measuring point for nuclear magnetic resonance measurement, so as to measure data or graphics and transient electromagnetic The measured resistivity anomaly is compared to judge whether the resistivity anomaly measured by transient electromagnetic is the authenticity of the target layer;

c. Keep the transmitting coil 8 and other measurement conditions unchanged, then switch the instrument to the transient electromagnetic working mode, measure this point, and obtain its attenuation curve;

d. Repeat the process of step b and step c for each measuring point with low resistance anomaly, until all abnormal measuring points are measured by the two geophysical methods.

Beneficial effect:

Using one set of equipment to realize the functions of the two instruments reduces equipment investment and brings into play the respective advantages of the two instruments. At the same time, it overcomes the shortcomings of transient electromagnetic instruments such as small emission current, low signal-to-noise ratio, and poor anti-interference ability. The signal-to-noise ratio of the instrument improves the detection efficiency and accuracy.

Drawings and Description of Drawings

Figure 1 is a structural block diagram of the nuclear magnetic resonance and transient electromagnetic instrument

Fig. 2 is a structural block diagram of high-power power supply 4

Fig. 3 is 6, 7, 8, 9, 10, connection relationship diagram in accompanying drawing 1

Fig. 4 is a structural block diagram of the frequency selection amplifying unit 11

Fig. 5 is a structural block diagram of broadband amplifying unit 13

Fig. 6 is a structural block diagram of signal acquisition unit 14

1 computer, 2 main control unit, 3 launch control unit, 4 high-power power supply, 5 H bridge circuit, 6 working mode switch, 7 matching capacitor, 8 transmitting coil, 9 diode, 10 relay, 11 frequency selection amplifier unit, 12 receiving coil, 13 broadband amplification unit, 14 signal acquisition unit, 15 receiving control unit,

Detailed ways

Below in conjunction with accompanying drawing and embodiment describe in further detail:

The computer 1 is connected to the main control unit 2 through a serial port or USB port, the emission control unit 3 is connected to the high-power power supply 4 through the data bus, connected to the H-bridge circuit 5 through the interactive signal line, and connected to the switching switch 6 through the control line. The power supply 4 is connected to the switch 6 via the H bridge 5, and the main control unit 2 is connected to the transmitting control unit 3 and the receiving control unit 15 through the SPI serial interface;

Transient electromagnetic working mode: the output end of the H-bridge 5 is directly connected to the two ends of the transmitting coil 8 to generate a transient electromagnetic signal, and the receiving coil 12 sends the transient electromagnetic signal to the broadband amplification unit 13 for signal conditioning and then sends it to the signal acquisition unit 14 and receiving control unit 15;

NMR working mode: the output terminals of the two bridge arms of the H-bridge 5 are connected to the matching capacitor 7 and the transmitting coil 8, and the frequency selection amplifying unit 11 is connected to the transmitting coil 8 through the relay 10, and the signal is sent to the signal acquisition unit 14 With the reception control unit 15 , the two diodes 9 are connected in reverse to themselves and connected to the resonant capacitor 7 .

The coupled nuclear magnetic resonance and transient electromagnetic apparatus and its method work according to the following method steps:

a. Select the combined nuclear magnetic resonance and transient electromagnetic instrument in the transient electromagnetic working mode, adopt the method of large loop, lay the transmitting coil 8 and place the receiving coil 12 around each measuring point, and use the transient electromagnetic method to detect fast The characteristics of each measuring point in the survey area are measured. After the measurement is completed, the transient electromagnetic data is initially processed to find out the low resistivity point in the survey area and calibrate the abnormal measuring point with low resistivity. ;

b. Switch the combined nuclear magnetic resonance and transient electromagnetic instrument to the nuclear magnetic resonance working mode, and lay the transmitting coil 8 centered on the calibrated abnormal measuring point for nuclear magnetic resonance measurement, so as to measure data or graphics and transient electromagnetic The measured resistivity anomaly is compared to judge whether the resistivity anomaly measured by transient electromagnetic is the authenticity of the target layer;

c. Keep the transmitting coil 8 and other measurement conditions unchanged, then switch the instrument to the transient electromagnetic working mode, measure this point, and obtain its attenuation curve;

d. Repeat the process of step b and step c for each measuring point with low resistance anomaly, until all abnormal measuring points are measured by the two geophysical methods.

The computer 1 and the main control unit 2 are connected through a serial port or a USB interface to transmit control instructions and detection data. The main control unit 2 of the instrument system coordinates the work of the emission control unit 3 and the reception control unit 15 and controls the working mode. switch. The main control unit 2 communicates with the transmitting control unit 3 and the receiving control unit 15 through the SPI serial interface at a rate of 500kbit/s.

The signal transmission part is composed of a transmission control unit 3, a high-power power supply 4, an H bridge circuit 5, a switch 6, a matching capacitor 7 and a transmission coil 8; the transmission control unit 3 is composed of a single-chip microcomputer with PWM output capability and related logic circuits. It mainly completes the charging control of the high-power power supply 4, the generation of the driving signal of the H-bridge circuit 5, the monitoring of the transmitter state and the switching of the working mode. The transmission control unit 3 controls the charging of the capacitor in the high-power power supply 4 by detecting the voltage of the high-power power supply 4 to provide high-power instantaneous power supply for the transmitter.

The 5VDC-DC converter provides working power for the emission control unit 3, and the emission control unit 3 monitors the voltage of the large-capacity capacitor in real time through the ADC. When the capacitor voltage does not meet the requirements, the emission control unit 3 generates a control signal through the DAC to adjust the boost The output voltage of the DC-DC converter charges the large-capacity capacitor, keeps the voltage across the large-capacity capacitor at a stable value, and provides high-power transmission power for the transmitter.

The emission control unit 3 provides the drive circuit with two TTL-level control signals with opposite logic and a certain dead time; the drive circuit converts the control signal to drive the H-bridge 5; the H-bridge 5 is composed of two bridge arms Each bridge arm has two high-power IGBT switch tubes, the H-bridge circuit 5 works at a switching frequency of 1KHz-3KHz, and the working current is about 200A, which is used to invert the DC power provided by the high-power power supply 4 into alternating current.

The working mode switching switch 6 is controlled by the emission control unit 3 and is used to switch the emission mode. Its signal path is 7 → 9 → 8 → 10 → 11. In terms of hardware, the output terminals of the two bridge arms of the H-bridge 5 are connected to both ends of the resonant circuit composed of the matching capacitor 7 and the transmitting coil 8, and the frequency of the receiving end is selected The amplification unit 11 is connected to the transmitter coil 8 via a relay 10 .

Transient electromagnetic signal flow direction: 6→8→12→13, the output terminal of H-bridge 5 is directly connected to the two ends of the transmitting coil 8 to generate transient electromagnetic signals, the receiving coil 12 receives the transient electromagnetic signals through coupling, and the receiving coil The induced signal is at the microvolt level, and the signal is connected to the broadband amplification unit 13 for signal conditioning.

In accompanying drawing 3, C1, C2 is the matching capacitor 7, L1 is the transmitting coil 8, D1 is the diode 9 of reverse connection, is used for releasing the residual energy in the transmitting coil, k1, k2 is the switching switch of switching the transmitting mode 6, k3 is the receiving signal changeover switch 10.

The specific working mode switching process is as follows: when the system works in the nuclear magnetic resonance mode, the transmitting control unit 3 controls the switch k1 to switch to both ends, the switch k2 is closed, the receiving control unit 15 controls k3 to open, and the matching capacitors 7 C1, C2 And the diode 9 D1 and the transmitting coil 8 L1 form a resonant circuit to transmit a high-power sinusoidal signal. After the system stops transmitting, after a delay of 40-70 ms, after the remaining energy in the transmitting coil 8 is released, the receiving control unit 15 controls the switch k3 to close, and the transmitting coil 8 is used as a receiving coil to connect with the frequency-selective amplifying unit 11 Get up and complete the reception of the nuclear magnetic signal. And when the system needs to switch to the transient electromagnetic method working mode, the switch k1 is switched to one end, the switch k2 is turned on, and the switch k3 is turned on. At this time, the transmitting coil 8 is directly connected to the two ends of the H bridge 5 as the load of the H bridge circuit, and the resonant capacitor 7 C1, C2 and diode 9 D1 are not connected to the transmitting main circuit, and the transmitter utilizes the transmitting coil 8 to transmit high power transient electromagnetic signal. The receiving end adopts the method of large loop, does not move the transmitting coil 8, uses the transient electromagnetic receiving coil 12 to realize the reception of the transient electromagnetic receiving signal, and preprocesses the signal through the broadband floating point amplification unit 13 to complete the transient Electromagnetic signal collection.

The frequency-selective amplifying unit 11 is composed of a nuclear magnetic resonance impedance matching network, a nuclear magnetic resonance preamplifier, an LC frequency-selective amplifier, a power frequency notch filter and a post-stage amplifier. The center frequency of the frequency selection amplifying unit 11 can be adjusted within the range of 1kHz-3kHz, and the amplification factor at the center frequency is 400,000 times. A high-performance power filter is added between the power supply of the nuclear magnetic resonance preamplifier and the impedance matching network and the power supply of the post-stage amplifying circuit to reduce the transmission interference generated by different stages of amplifying circuits.

The broadband amplifying unit 13 is composed of a transient electromagnetic impedance matching network, a transient electromagnetic preamplifier, a broadband filter, a power frequency notch filter and a post-stage amplifier. The power distribution method of the broadband amplifying unit 13 is the same as that of the frequency selective amplifying unit 11 . The transient electromagnetic impedance matching network can ensure good impedance matching for the amplifying circuit and the receiving coil in the range of tens of hertz to tens of kilohertz. The transient electromagnetic preamplifier uses an instrument amplifier chip with high input impedance, low noise, and low offset voltage to reduce the noise of the instrument system.

The signal acquisition unit 14 is based on the requirements of the nuclear magnetic resonance signal and the transient electromagnetic signal on the sampling rate and sampling accuracy. The signal acquisition unit 14 has a sampling rate of 1 MHz and a sampling accuracy of 16 bits.

The signal collected by the front-end amplifier is a single-ended AC signal, and the AD used in the system can only collect DC double-ended differential signals. The single-ended to double-ended module completes the signal conversion function, and the converted signal is sent to the AD acquisition module. Due to the sampling rate Higher, the signal acquisition unit 14 uses the method of CPLD+FIFO to buffer and store the high-speed collected data, and then the receiving control unit 15 reads the data in the FIFO and sends it to the memory.

The specific working methods of the nuclear magnetic resonance and transient electromagnetic instrument in the field:

In a survey area with unknown underground conditions, before the detection, the plane of the survey area is firstly divided into multiple survey lines according to a certain distance, and each survey line is divided into several survey points as required.

Step 1: Let the combined instrument work in the transient electromagnetic mode, and lay the transmitting coil 8 and place the receiving coil 12 around each measuring point in the form of a large loop. Utilizing the rapid detection characteristics of the transient electromagnetic method, each measuring point in the survey area is measured. After the measurement, the transient electromagnetic data is preliminarily processed to find out the low resistivity in the survey area and correct the deviation of the resistivity. Low abnormal measuring point calibration;

Step 2, switch the combined instrument to the nuclear magnetic resonance working mode, and lay the transmitting coil 8 centered on the calibrated measuring point, and perform the fixed-point nuclear magnetic resonance measurement work to measure the data or graphics and the resistance measured by the transient electromagnetic Compared with the abnormal resistivity, it is used to judge whether the abnormal resistivity measured by transient electromagnetic is the authenticity of the target layer.

Step 3: Keep the transmitting coil and other measurement conditions unchanged, then switch the instrument to the transient electromagnetic working mode, measure this point, and obtain its attenuation curve.

Step 4: Repeat the process of step 2 and step 3 for each measuring point with low resistance anomaly, until all measuring points have been measured by the two geophysical methods.

Data processing of the measured data can be used to correct the NMR data, and can be used to weaken the influence of the low-frequency natural field on the detection results, and improve the detection efficiency and result accuracy.

Claims (2)

1, a kind of nuclear magnetic resonance and transient electromagnetic combined instrument and method thereof, it is characterized in that, computing machine (1) is connected with main control unit (2) by serial ports or USB mouth, emission controlling unit (3) is connected with large power supply (4) by data bus, be connected with H bridge circuit (5), be connected with change-over switch (6) by the interactive signal line by control line, large power supply (4) is connected with change-over switch (6) through H bridge circuit (5), and main control unit (2) is connected with emission controlling unit (3), reception control module (15) by the SPI serial line interface;

---the transient electromagnetic mode of operation: H bridge circuit (5) output terminal directly is connected generation transient electromagnetic signal with transmitting coil (8) two ends, and receiving coil (12) is sent the transient electromagnetic signal into broadband amplifying unit (13) and carried out giving signal gathering unit (14) again and receiving control module (15) behind the signal condition;

---the nuclear magnetic resonance mode of operation: two brachium pontis output terminals of H bridge circuit (5) with join humorous electric capacity (7) and be connected with transmitting coil (8), frequency-selecting amplifying unit (11) is connected with transmitting coil (8) by relay (10), and signal sent into signal gathering unit (14) and receive control module (15), two reverse connections of diode self, and be connected with resonant capacitance (7).

2, according to the described nuclear magnetic resonance of claim 1 and transient electromagnetic combined instrument and method thereof, it is characterized in that step work by the following method:

A. nuclear magnetic resonance and transient electromagnetic combined instrument are chosen under the transient electromagnetic mode of operation, adopt the mode of big loop line, lay transmitting coil (8) and place receiving coil (12) around each measuring point, utilize transient electromagnetic method to survey characteristics fast, measure surveying interior each measuring point in district, after measurement finishes, the transient electromagnetic data are carried out preliminary processing, find out and survey resistivity point on the low side in the district, and resistivity unusual measuring point on the low side is demarcated;

B. nuclear magnetic resonance and transient electromagnetic combined instrument are switched under the nuclear magnetic resonance mode of operation, and be that the center is laid transmitting coil (8) and carried out Nuclear Magnetic Resonance Measurement work with the unusual measuring point of having demarcated, compare to record the resistivity anomaly that data or figure and transient electromagnetic surveyed, in order to judge whether the resistivity anomaly that transient electromagnetic is surveyed is the true and false of zone of interest;

C. keep transmitting coil (8) and other measuring condition constant, again instrument is switched to the mode of operation of transient electromagnetic, this point is measured, obtain its die-away curve;

D. each the process that the unusual measuring point of low-resistance all repeats step b and step c occurred, all use two kinds of geophysical prospecting method measurements to finish up to all unusual measuring points.

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