A nuclear magnetic resonance based logging while drilling transmitting device

Abstract

The application belongs to the technical field of nuclear magnetic resonance logging while drilling, and proposes a nuclear magnetic resonance logging while drilling transmitting device, which comprises a main control acquisition processing module, a driving module, a power pulse transmitting module, an antenna interface module and a high-voltage power supply. The main control acquisition processing module is used for receiving a main control signal, converting the signal and outputting the signal to the driving module as a driving signal. The driving module is used for receiving a front-stage signal and outputting the signal to a rear-stage power pulse transmitting circuit. The power pulse transmitting module lifts up the direct current power supply to generate a pulse meeting the nuclear magnetic resonance transmitting requirement. The antenna interface module adopts parallel resonance, so that the voltage provided by the power transmitting circuit is the resonance voltage for transmitting. The high-voltage power supply provides the required power supply energy for the circuit. The application can be implemented under the conditions of high temperature, high pressure, strong vibration and narrow space, and provides a high-power and high-energy-efficiency radio frequency transmitting circuit for the development of a nuclear magnetic resonance logging while drilling instrument.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nuclear magnetic resonance logging while drilling, and particularly relates to a nuclear magnetic resonance logging while drilling transmitting device. BACKGROUND

[0002] Compared with the traditional single measurement technology, the nuclear magnetic resonance logging can provide more abundant formation parameters, and comprehensively covers the three basic problems of well logging about hole, permeability and saturation. The inversion speed is fast, the signal strength is high, and it is not affected by the formation characteristics. It is the only method that can distinguish the bound water fluid in the formation, and can directly detect the free fluid seepage volume characteristics in any rock formation. It provides a large amount of valuable reference basis for evaluating the geological structure and reservoir characteristics. It has great advantages for the measurement of complex terrain and topography, formation permeability, etc. It is the most advanced logging method at present.

[0003] The nuclear magnetic resonance detection instrument is an instrument system with high complexity, high difficulty and multi-disciplinary intersection. Especially for the ultra-low field nuclear magnetic resonance detection used for geophysical exploration, it is very difficult to generate a magnetic field that can make protons (hydrogen nuclei) transition from a low energy state to a high energy state. SUMMARY

[0004] In order to be able to generate a magnetic field that can make protons (hydrogen nuclei) transition from a low energy state to a high energy state, the present application proposes a nuclear magnetic resonance logging transmitting device. Under the control of the host computer, the device generates a reference signal at the Larmor frequency, and cooperates with the high-voltage power supply to realize the bootstrap of the transmitting voltage through the control of the double full-bridge circuit, and connects with the antenna through the antenna interface module to form a magnetic field that can resonate with protons (hydrogen nuclei), so that the nuclear magnetic moment in the low energy state transitions to the high energy state by absorbing the energy provided by the alternating magnetic field. The nuclear magnetic resonance transmitting device generates a series of high-power pulses with pulse frequency, pulse amplitude and transmission period meeting the requirements of nuclear magnetic resonance, realizes the excitation of the transmitting antenna, effectively excites the formation to generate nuclear magnetic resonance echo signals, and is the core of realizing the nuclear magnetic resonance logging detection task. The high-power pulse meeting the requirements of nuclear magnetic resonance mainly includes the following two points: 1. The frequency of the transmitted pulse is the Larmor frequency, because at the Larmor frequency, the hydrogen nuclei can occur resonance transition between the magnetic energy levels; 2. Since the drilling probe adopts the "Inside-out" scheme, i.e. putting a permanent magnet into the wellbore (Inside), and establishing a static magnetic field much higher than the geomagnetic field in the formation outside the wellbore (Outside), so as to realize the monitoring of the formation signal, which requires that the excitation power of the antenna is very high. Therefore, for the nuclear magnetic resonance transmitting device, the power output by the power pulse transmitting module needs to be very high, and the high-power radio frequency pulse is transmitted to the antenna, and then emitted to the formation by the antenna to excite the hydrogen nuclei and generate nuclear magnetic resonance.

[0005] The main control acquisition processing module is used for receiving a main control signal and converting and inputting the main control signal to the driving module, wherein the main control signal is a control signal given by an upper computer, and a frequency of a reference signal of the control signal is a Larmor frequency;

[0006] The driving module is used for receiving an output signal of the front-stage main control acquisition processing module and outputting to a rear-stage power pulse emission module;

[0007] The power pulse emission module is used for lifting up direct current provided by a high-voltage power supply to generate a pulse meeting a requirement of nuclear magnetic resonance emission;

[0008] The high-voltage power supply provides required power supply energy for the emission device;

[0009] Compared with the prior art, the application requires that a pulse emission circuit creates a high-frequency, high-power, high-voltage and large-current pulse to excite a stratum nuclear magnetic resonance echo, and requires a power semiconductor device and an electronic circuit with excellent performance to support, and a silicon carbide metal-oxide semiconductor field effect transistor (SiC MOSFET) has excellent performance characteristics in a high-frequency, high-voltage and high-temperature environment, so the power semiconductor device used in the application is SiC MOSFET, which can provide a radio frequency emission signal with a large power and a high energy efficiency index for a while-drilling nuclear magnetic resonance logging instrument under the conditions of high temperature, high pressure, strong vibration and narrow space. The emission frequency band is wide and the resolution is high. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 , a system block diagram;

[0011] Figure 2 , a driving chip working logic block diagram;

[0012] Figure 3 , a power pulse emission module structure diagram;

[0013] Figure 4 , a control signal timing diagram;

[0014] Figure 5a , a current flow direction diagram of one preferred example of the application;

[0015] Figure 5b , a current flow direction diagram of one preferred example of the application;

[0016] Figure 5c , a current flow direction diagram of one preferred example of the application;

[0017] Figure 5d , a current flow direction diagram of one preferred example of the application;

[0018] Wherein, 3-1, commutating full-bridge circuit, 3-2, bootstrap isolation circuit, 3-3, transmitting full-bridge circuit, 3-4, antenna module, Q1-Q8 are field effect tubes, C1, C2 are energy storage short section capacitors, D1, D2 are diodes, R1-R4 are resistors, T1-T8 are field effect tube working stages. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application more clear, the following drawings and examples, the specific embodiments of the present application are described in further detail. The following examples are only used to explain the present application, and are not used to limit the present application.

[0020] Referring to Figure 1 The present application has a master control acquisition processing module, a driving module, a power pulse transmitting module, an antenna module and a high voltage power supply. The driving module is composed of a digital control and signal conversion circuit and a signal monitoring and protection circuit. The power pulse transmitting module is composed of an isolation circuit, a commutating full-bridge circuit, a bootstrap isolation circuit and a transmitting full-bridge circuit.

[0021] The pulse transmitting module needs to be matched with the inherent frequency of the antenna to create the required radio frequency field B1, which is perpendicular to the static magnetic field B0 of the antenna magnet, so as to make the hydrogen nucleus atoms in the detection area rotate in the direction and create the conditions for nuclear magnetic resonance. In order to make the strength of the radio frequency field B1 sufficient, a large pulse current needs to pass through the transmitting antenna coil. The atomic nucleus with magnetic moment has a resonance frequency, called Larmor frequency, which depends on the magnetic selection ratio and the applied magnetic field strength F = γB0 / 2π, where γ is the rotation ratio or the proportion factor. The transmitting reference frequency is determined according to the Larmor frequency, and the driving control signal is generated. The control signal output by the host computer is a differential signal based on the CPMG pulse sequence. The master control acquisition processing module receives the differential signal given by the host computer and converts the differential signal into a single-ended signal, which is output to the driving module.

[0022] The driving module receives the converted master control signal, amplifies the 5V control signal to a large current 20V control signal, so that the master control acquisition processing module can quickly control the conduction and turn-off of the field effect tube in the power pulse transmitting module. The driving module in the present application includes a driving chip and a magnetic ring. The driving chip uses CHT-HADES2P and CHT-HADES2S. CHT-HADES2P is used for modulation, CHT-HADES2S is used for demodulation, and the magnetic ring is used for signal isolation. Figure 2As shown, the logic block diagram of two chips processing driving signal. Control signal is input to CHT-HADES2P, the chip is modulated by OOK (binary on-off keying), according to the characteristics of CHT-HADES2P chip, the converted master control signal is modulated into high frequency signal to the back stage for transmission, through a specific magnetic ring, because the magnetic ring of different materials, the frequency band is different, so the invention uses nickel zinc magnetic ring to isolate the front and rear stage strong and weak signal, input to CHT-HADES2S, the chip demodulates the modulated high frequency signal transmitted from the front stage, and outputs a 20V driving control signal with large current. Then it is transmitted to the back stage and input to the field effect tube in the power pulse emission circuit, so that the driving circuit can control the field effect tube to turn on and off.

[0023] Referring to Figure 3 As shown, the power pulse emission module is used to convert the 600V DC provided by the high voltage power supply into a 2400V high power radio frequency pulse after chopping, which is divided into three parts, namely commutation full bridge circuit, bootstrap isolation circuit and emission full bridge circuit; the commutation full bridge circuit includes four field effect tubes Q1, Q2, Q7 and Q8, Q1 and Q2 form a bridge arm, Q7 and Q8 form a bridge arm, and the two bridge arms are connected to the high voltage power supply; the commutation full bridge circuit is connected with the bootstrap isolation circuit, and the control signals of the four field effect tubes are the 20V control signals with large current output by the driving module; the bootstrap isolation circuit includes energy storage short section capacitors C1 and C2, isolation diodes D1 and D2, and resistors R1-R4, wherein R1>>R2 and R3>>R4; the commutation full bridge circuit and the emission full bridge arm are blocked through D1, D2 and resistors R1 and R3; the energy storage short section capacitors C1 and C2 are connected in parallel with resistors R1 and R3, which can raise the voltage to nearly one time; the bootstrap isolation circuit is connected with the front stage commutation full bridge to raise the voltage; the raised circuit is connected with the emission full bridge circuit; the emission full bridge circuit includes four field effect tubes Q3, Q4, Q5 and Q6, Q3 and Q4 form a bridge arm, and Q5 and Q6 form a bridge arm; the control signals of the four field effect tubes are the 20V control signals with large current output by the driving module, and the output end of the emission full bridge circuit is connected with the emission antenna module.

[0024] The working process of the power pulse transmitting module is as follows: the high-voltage power supply is taken as an electric energy source and is input to the commutating full-bridge circuit, the commutating full-bridge circuit realizes commutation of the power transmitting pulse, ensures phase matching of the transmitting full-bridge circuit, and creates a symmetrical dynamic voltage for the power transmitting pulse; the bootstrap isolation circuit is connected with the preceding commutating full-bridge, and realizes bootstrap lifting of the voltage; the bootstrap isolation circuit is input to the transmitting full-bridge circuit, the transmitting full-bridge circuit is connected in parallel with the antenna module, the transmitting antenna interface adopts a low-inductance design and the resonant circuit is a simple parallel resonant circuit of frequency modulation, so as to ensure that the maximum voltage provided by the power pulse transmitting module is the resonant voltage of the antenna, wherein the high-voltage power supply is a 600V DC power supply. The specific working process is as follows:

[0025] Referring to Figure 4 the driving control signal timing diagram is shown. The conduction and turn-off of each field effect tube in the double full-bridge circuit can be divided into different working stages, and each working stage corresponds to T1-T8 in the timing diagram, a total of eight working stages. Among them, Q1Q8 conduction is T1 stage, Q3Q6 conduction is T2 stage, Q3Q6 turn-off is T3 stage, Q1Q8 turn-off is T4 stage, Q2Q7 conduction is T5 stage, Q4Q5 conduction is T6 stage, Q4Q5 turn-off is T7 stage, and Q2Q7 turn-off is T8 stage. Among them, T1-T4 is the process of creating a positive voltage for the transmitting pulse, and T5-T8 is the process of creating a negative voltage for the transmitting pulse.

[0026] Referring to Figure 3 in order to be able to create as high a bootstrap voltage as possible, R1>>R2, R3>>R4 should be met. Before starting to work, all driving signals are low, and all field effect tubes are turned off. Since R1>>R2, R3>>R4, the voltage across C1 and C2 is close to 600V, and the voltage across the antenna is 0.

[0027] In T1 stage, Q1 and Q8 are turned on, at this time, the potential of point B is 600V, the potential of point A is 1200V, the potential of point D is 0V, and the voltage across C2 is supplemented from close to 600V to 600V. As Figure 5a shown, it is a current flow diagram of T1 working stage.

[0028] In the T2 stage, Q3 and Q6 are turned on, at this time, Q1 and Q8 are still in the on state, the voltage at point A is applied to the upper end of the antenna, and the lower end is connected to 0V. If it is an initial transmission period, the voltage across the antenna is 0, which is applied to the resonant capacitor of the antenna, which is equivalent to a short circuit, and most of the current will generate a large charging current to charge the resonant capacitor, and the voltage across the resonant capacitor will rise sharply; if it is in the normal working period, the resonant capacitor of the antenna resonates to the maximum positive voltage across the capacitor, and after Q3 and Q6 are turned on, the voltage across the capacitor is supplemented to 1200V, at this time, the current in the antenna coil is in the process of changing from negative to positive, and when the voltage reaches the highest point, the current starts to increase positively. As shown in FIG. 6, it is a current flow diagram in the T2 working stage. Figure 5b

[0029] In the T3 stage, Q3 and Q6 are turned off, the antenna is free to oscillate, the voltage across the resonant capacitor decreases from about 1200V, and the current in the coil increases positively. As shown in FIG. 7, it is a current flow diagram in the T3 working stage. Figure 5c

[0030] In the T4 stage, Q1 and Q8 are turned off, the antenna is still in a free resonant state, the voltage across the resonant capacitor decreases from positive to negative, the current in the coil reaches the maximum and starts to decrease, and the resonant capacitor starts to charge reversely. As shown in FIG. 8, it is a current flow diagram in the T4 working stage. Figure 5d

[0031] Since the principles of positive and negative working processes are the same, only the T1-T4 working processes are introduced.

[0032] Due to the large working voltage, the double full-bridge is very strict in the accuracy of the control signal, in order to prevent the safety hazards caused by the direct through of the upper and lower field effect tubes, a signal monitoring and protection circuit is specially provided, if the signal is found to have a problem, the high-voltage power supply input is directly turned off.

[0033] Overall, the 600V DC high voltage is processed by chopping, and becomes a high-power radio frequency pulse with a peak value of 2400V, the radio frequency pulse is transmitted to the antenna, and is emitted to the ground layer by the antenna to excite hydrogen nuclei, so as to generate nuclear magnetic resonance.

[0034] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.​​​

Claims

1. A nuclear magnetic resonance based logging while drilling transmitting device comprising a logging while drilling probe, characterized in that Comprise: The host control acquisition processing module, the drive module, the power pulse emission module, the high voltage power supply and the antenna interface module; The host computer sends the host control signal under the Larmor frequency to the host control acquisition processing module, the host control acquisition processing module converts and outputs 8 paths after the host control signal, each converted host control signal is input into a drive module, the drive module generates the drive signal capable of driving the field effect transistor in the power pulse emission module, the power pulse emission module under the control of the drive signal lifts the direct current provided by the high voltage power supply, generates a series of high power pulses with pulse frequency, pulse amplitude and emission period meeting the requirements of nuclear magnetic resonance, realizes the excitation of the transmitting antenna, effectively excites the formation of nuclear magnetic resonance echo signal; The high power pulse meeting the requirements of nuclear magnetic resonance includes the following two points:

1. The transmitted pulse frequency is the Larmor frequency, under the Larmor frequency, the hydrogen nucleus can occur resonance transition between the magnetic energy levels; 2. The while-drilling probe adopts the "Inside-out” scheme, Inside refers to placing a permanent magnet into the wellbore, Outside refers to establishing a static magnetic field much higher than the geomagnetic field in the formation outside the wellbore, thereby realizing the monitoring of the formation signal, the high power pulse output by the power pulse emission module is transmitted to the antenna, and the antenna emits into the formation to excite the hydrogen nucleus to generate nuclear magnetic resonance.

2. A nuclear magnetic resonance based logging-while-drilling transmitting device according to claim 1, wherein, Further, the host control signal given by the host computer is a differential signal, and the host control acquisition processing module converts the differential signal into a single-ended signal.

3. A nuclear magnetic resonance based logging-while-drilling transmitting device according to claim 1, wherein, Further, the drive module amplifies the converted 5V host control signal into a 20V control signal with large current, which is used to enable the host control acquisition processing module to quickly control the conduction and turn-off of the field effect transistor in the power pulse emission module; Further, by setting the monitoring and protection circuit, the accuracy of the converted host control signal is monitored in real time to prevent the safety hazard of the field effect transistor bridge arm short circuit in the power pulse emission module.

4. The NMR-based LWD transmitting device of claim 3, wherein, The drive module comprises a drive chip and a magnetic ring, the drive chip adopts CHT-HADES2P and CHT-HADES2S, wherein CHT-HADES2P is used for modulation, CHT-HADES2S is used for demodulation, and the magnetic ring is used for signal isolation; The working process of the drive module is that the converted host control signal is input into CHT-HADES2P, the chip modulates the converted host control signal into a high-frequency signal through OOK binary on-off keying modulation for transmission to the rear stage, and after the magnetic ring, the strong and weak electric signals of the front and rear stages are isolated, and input into CHT-HADES2S, the chip demodulates the modulated high-frequency signal transmitted from the front stage into the original Larmor frequency drive control signal.

5. The NMR-based LWD transmitting device of claim 1, wherein, The drive module and the power pulse emission module are connected through an isolation circuit to realize the isolation of strong and weak electric signals of the front and rear stages.

6. The nuclear magnetic resonance based logging-while-drilling transmitting device of claim 1, wherein, The power pulse emission module is used to chop the 600V direct current provided by the high voltage power supply into 2400V high power radio frequency pulse.

7. A nuclear magnetic resonance based logging-while-drilling transmitting device according to claim 6, wherein, The power pulse emission module is specifically divided into three parts, which are commutation full-bridge circuit, bootstrap isolation circuit and emission full-bridge circuit. The commutating full-bridge circuit comprises four field effect tubes Q1, Q2, Q7 and Q8, Q1 and Q2 form a bridge arm, Q7 and Q8 form a bridge arm, the two bridge arms are connected to a high-voltage power supply respectively, the commutating full-bridge circuit is connected with a bootstrap isolation circuit, and the control signals of the four field effect tubes are 20V control signals of large current output by a driving module. The bootstrap isolation circuit comprises energy storage short-circuit capacitors C1 and C2, isolation diodes D1 and D2, resistors R1, R2, R3 and R4, wherein R1>>R2, R3>>R4; D1, C1 and R2 are connected in series, the positive electrode of D1 is connected with the drain electrode of Q1, R2 is connected with the source electrode of Q2, and the other end of R2 is connected with the drain electrode of Q2; D2, C2 and R4 are connected in series, the positive electrode of D2 is connected with the drain electrode of Q7, R4 is connected with the source electrode of Q8, and the other end of R4 is connected with the drain electrode of Q8; R1 is connected with the energy storage short-circuit capacitor C1 in parallel, and R3 is connected with the energy storage short-circuit capacitor C2 in parallel, thereby playing a role of self-boosting to raise the voltage by nearly one time; the commutating full-bridge circuit and the transmitting full-bridge bridge arm are blocked through D1, D2 and resistors R1 and R3, the bootstrap isolation circuit is connected with the front-stage commutating full-bridge, and the voltage is self-boosted and raised; the raised circuit is connected with the transmitting full-bridge circuit. The transmitting full-bridge circuit comprises four field effect tubes Q3, Q4, Q5 and Q6, Q3 and Q4 form a bridge arm, Q5 and Q6 form a bridge arm, the negative electrode of D1 is connected with the drain electrode of Q3, the negative electrode of D2 is connected with the drain electrode of Q5, and the control signals of the four field effect tubes are 20V control signals of large current output by a driving module; and the output end of the transmitting full-bridge circuit is connected with a transmitting antenna module.

8. The NMR-based LWD transmitting device of claim 7, wherein, The working process of the power pulse transmitting module is as follows: a high-voltage power supply is taken as an electric energy source, is input into the commutating full-bridge circuit, the commutating full-bridge circuit realizes commutation of a power transmitting pulse, ensures phase matching of the transmitting full-bridge circuit, and creates a symmetrical dynamic voltage for the power transmitting pulse; the bootstrap isolation circuit is connected with the front-stage commutating full-bridge, and the voltage is self-boosted and raised; the bootstrap isolation circuit is input into the transmitting full-bridge circuit, the transmitting full-bridge circuit is connected with an antenna interface module in parallel, the antenna interface module adopts a low-inductance design and a simple parallel resonant circuit as a resonant circuit, so as to ensure that the maximum voltage provided by the power pulse transmitting module is the resonant voltage of the antenna, and the high-voltage power supply is a 600V direct-current power supply.

9. The NMR-based LWD transmitting device of claim 7, wherein, The power pulse emission module includes eight field effect tubes Q1-Q8, the turn-on and turn-off of the field effect tubes can be divided into different working stages, each working stage corresponds to T1-T8 in the timing, a total of eight working stages, wherein Q1Q8 is turned on as T1 stage, Q3Q6 is turned on as T2 stage, Q3Q6 is turned off as T3 stage, Q1Q8 is turned off as T4 stage, Q2Q7 is turned on as T5 stage, Q4Q5 is turned on as T6 stage, Q4Q5 is turned off as T7 stage, and Q2Q7 is turned off as T8 stage, wherein T1-T4 is the process of creating a positive voltage for the emission pulse, and T5-T8 is the process of creating a negative voltage for the emission pulse.

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