Gradient resistivity measurement system, instrument string, and logging system

Abstract

The application relates to the technical field of well logging, and discloses a gradient resistivity measurement system, an instrument string and a well logging system, which comprise a harnessed head and a telemetry instrument located on the instrument string, the harnessed head is provided with an electrode assembly, the telemetry instrument comprises a mounting position of a mud resistivity plate and corresponding data transmission devices; a gradient resistivity plate, which is detachably installed in the mounting position in a state that the mud resistivity plate is not installed in the mounting position, and is electrically connected with the electrode assembly and the data transmission devices respectively, is used for measuring the gradient resistivity of a formation through the electrode assembly, and sending the measurement result of the gradient resistivity to the data transmission devices to be transmitted to a ground system. In this way, the problem that the effect of a mode of separately manufacturing an electrode sub to realize the gradient resistivity measurement of the formation is poor is solved, the length of the instrument string and the number of connection points are not affected, the cost is reduced, and the gradient resistivity of the formation and other well logging items in the instrument string can be completed at one time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of well logging technology, and particularly relates to a gradient resistivity measurement system, an instrument string and a well logging system. BACKGROUND

[0002] Well logging is one of the important technologies in the field of exploration and plays a very important role in the process of oil and gas exploration and development.

[0003] In the current well logging system, sound and induction combination is commonly used to complete the acquisition of well logging data. However, in some well logging systems, the measurement of the gradient resistivity of the formation is not designed, and if the gradient resistivity curve of the formation is to be measured, a separately designed and manufactured electrode sub needs to be hung in the instrument string to complete the measurement, which not only increases the cost, but also increases the length of the instrument string, leading to an increase in the risk of construction, and increases the number of connection points, leading to an increase in the failure points. It can be seen that the way of separately manufacturing an electrode sub to realize the measurement of the gradient resistivity of the formation is not good. CONTENT OF THE INVENTION

[0004] The present application aims to at least provide a gradient resistivity measurement system, an instrument string and a well logging system, which can at least solve the problem of the poor effect of the way of separately manufacturing an electrode sub to realize the measurement of the gradient resistivity of the formation, and can at least achieve the effect of reducing the influence on the length of the instrument string and the number of connection points, and reducing the cost.

[0005] According to a first aspect of the present application, a gradient resistivity measurement system is provided, comprising:

[0006] a hanger on the instrument string, the hanger having an electrode assembly, and a telemetry instrument, the telemetry instrument comprising a mounting position of a mud resistivity plate and a corresponding data transmission device;

[0007] the gradient resistivity plate, in a state where the mud resistivity plate is not installed in the mounting position, being detachably installed in the mounting position and being electrically connected with the electrode assembly and the data transmission device respectively, for measuring the gradient resistivity of the formation through the electrode assembly and sending the measurement result of the gradient resistivity to the data transmission device; and the data transmission device being used for transmitting the measurement result of the gradient resistivity to a ground system.

[0008] Optionally, the gradient resistivity plate comprises a waveform generator, a shaping circuit, a constant current source circuit, a measurement circuit and a rectifier filter circuit.

[0009] The waveform generator is used for generating a waveform signal and outputting.

[0010] The shaping circuit is connected with the waveform generator, and is configured to perform shaping processing on the waveform signal to obtain a control signal, and provide the control signal to the rectification filtering circuit.

[0011] The constant current source circuit is connected with the waveform generator and the measurement circuit respectively, and is configured to generate a constant current signal as a power supply signal according to the waveform signal, and provide the power supply signal to the measurement circuit.

[0012] The measurement circuit is further connected with the constant current source circuit, the electrode assembly and the rectification filtering circuit respectively, and is configured to, in a logging state, provide the power supply signal to the formation through the electrode assembly, and obtain a measurement signal of the gradient resistivity through the electrode assembly, and provide the measurement signal to the rectification filtering circuit.

[0013] The rectification filtering circuit is further connected with the data transmission device, and is configured to, under the control of the control signal, perform rectification filtering processing on the measurement signal to obtain a measurement result of the gradient resistivity, and send the measurement result of the gradient resistivity to the data transmission device.

[0014] Optionally, the rectification filtering circuit comprises a first amplification circuit, a rectification circuit and a filtering circuit.

[0015] The first amplification circuit is connected with the measurement circuit and the rectification circuit respectively, and is configured to amplify the measurement signal to obtain a first amplified signal, and provide the first amplified signal to the rectification circuit.

[0016] The rectification circuit is further connected with the shaping circuit and the filtering circuit respectively, and is configured to, under the control of the control signal, rectify the first amplified signal to obtain a first direct current signal, and provide the first direct current signal to the filtering circuit.

[0017] The filtering circuit is further connected with the data transmission device, and is configured to filter the first direct current signal to obtain a second direct current signal, the second direct current signal being the measurement result of the gradient resistivity; and send the second direct current signal to the data transmission device.

[0018] Optionally, the electrode assembly comprises a first electrode ring, a second electrode ring, a third electrode ring and a torpedo.

[0019] The first input end of the measuring circuit is connected with the first electrode ring, the second input end is connected with the second electrode ring, the third input end is connected with the torpedo, the fourth input end is connected with the output end of the constant current source circuit, the first output end is connected with the first input end of the rectification filter circuit, the second output end is connected with the second input end of the rectification filter circuit, and the third output end is connected with the third electrode ring, so as to provide the power supply signal to the formation through the third electrode ring and provide the signals of the first electrode ring and the second electrode ring to the rectification filter circuit in the logging state, and the measuring signal includes the signals of the first electrode ring and the second electrode ring.

[0020] The third input end of the measuring circuit is also grounded.

[0021] Optionally, the measuring circuit includes a first resistor, a second resistor, a third resistor, a first switch, a second switch and a third switch.

[0022] The fourth input end of the measuring circuit is connected with the first end of the first resistor and the third output end of the measuring circuit through the first switch respectively.

[0023] The second end of the first resistor is connected with the first end of the second resistor, and is also connected with the first input end and the first output end of the measuring circuit through the second switch respectively.

[0024] The second end of the second resistor is connected with the first end of the third resistor, and is also connected with the second input end and the second output end of the measuring circuit through the third switch respectively.

[0025] The second end of the third resistor is grounded.

[0026] The first switch, the second switch and the third switch are used for making the first end of the first resistor and the fourth input end of the measuring circuit, the second end of the first resistor and the first output end of the measuring circuit, and the second end of the second resistor and the second output end of the measuring circuit conductive when switched to the test state, so as to test the reference value of the measurement result of the gradient resistivity obtained by the rectification filter circuit; and making the fourth input end and the third output end of the measuring circuit, the first input end and the first output end of the measuring circuit, and the second input end and the second output end of the measuring circuit conductive when switched to the logging state, so as to measure the gradient resistivity underground.

[0027] Optionally, the shaping circuit includes a resistor unit, a first inverting circuit and a second inverting circuit.

[0028] The first inverting circuit is connected with the waveform generator through the resistance unit, and is also connected with the second inverting circuit, for inverting the waveform signal to obtain a first inverted signal, and providing the first inverted signal to the second inverting circuit.

[0029] The second inverting circuit is also connected with the rectification filtering circuit, for inverting the first inverted signal to obtain the second inverted signal, and providing the second inverted signal as the control signal to the rectification filtering circuit.

[0030] Optionally, the constant current source circuit comprises a second amplification circuit, a third amplification circuit and a fourth amplification circuit.

[0031] The second amplification circuit is connected with the waveform generator, the third amplification circuit and the fourth amplification circuit respectively, for differentially amplifying the waveform signal and a third amplified signal from the third amplification circuit to obtain a second amplified signal, and providing the second amplified signal to the fourth amplification circuit.

[0032] The fourth amplification circuit is also connected with the measurement circuit, for power amplifying the second amplified signal to obtain a fourth amplified signal, obtaining the power supply signal based on the fourth amplified signal and providing the power supply signal to the measurement circuit.

[0033] The third amplification circuit is also connected with the fourth amplification circuit, for amplifying the fourth amplified signal to obtain the third amplified signal, and providing the third amplified signal to the second amplification circuit, so that the fourth amplified signal is a constant current signal.

[0034] Optionally, the waveform generator comprises an oscillation circuit, a frequency division circuit and a comparison circuit.

[0035] The oscillation circuit is connected with the frequency division circuit, for generating an oscillation signal and providing the oscillation signal to the frequency division circuit.

[0036] The frequency division circuit is also connected with the comparison circuit, for frequency dividing the oscillation signal to obtain a first square wave signal, and providing the first square wave signal to the comparison circuit.

[0037] The comparison circuit is also connected with the shaping circuit and the constant current source circuit respectively, for comparing the first square wave signal and an output feedback signal of itself to obtain a second square wave signal, the second square wave signal being the waveform signal; and providing the second square wave signal to the shaping circuit and the constant current source circuit.

[0038] According to a second aspect of the present application, there is provided an instrument string comprising the gradient resistivity measurement system as described in any one of the above.

[0039] According to a third aspect of the present application, there is provided a logging system comprising a surface system and the instrument string as described above.

[0040] The present application has the following beneficial effects compared with the prior art:

[0041] In the present application, the electrode assembly on the bit head is used and the gradient resistivity plate is detachably installed in the installation position of the original mud resistivity plate in the telemetry instrument, the measurement of the gradient resistivity of the formation is realized through the gradient resistivity plate and the electrode assembly electrically connected thereto, and the measurement result of the gradient resistivity is transmitted to the surface system through the data transmission device corresponding to the mud resistivity plate. Since the bit head and the telemetry instrument are both existing structures on the instrument string, the influence on the length and the number of connection points of the instrument string is reduced, and the cost is also reduced. The gradient resistivity of the formation and other logging items in the instrument string can be completed at one time, and thus the problem that the effect of the way of separately manufacturing the electrode sub to realize the measurement of the gradient resistivity of the formation is poor is solved.

[0042] It can be understood that the beneficial effects of the second aspect to the third aspect can be referred to the related description in the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0043] One or more embodiments are illustrated by way of example in the figures that form a part of this patent document. These example are not intended to limit embodiments of the application, but to clarify and explain the principles of the at least one embodiment.

[0044] Figure 1 is a structural schematic diagram of a gradient resistivity measurement system provided by one embodiment of the present application;

[0045] Figure 2 is one of structural schematic diagrams of a gradient resistivity plate provided by another embodiment of the present application;

[0046] Figure 3 is a structural schematic diagram of a bit head provided by another embodiment of the present application;

[0047] Figure 4 is another structural schematic diagram of a gradient resistivity plate provided by another embodiment of the present application;

[0048] Figure 5 is a structural schematic diagram of an external calibration resistor network provided by another embodiment of the present application;

[0049] Figure 6 is a structural schematic diagram of a logging system provided by another embodiment of the present application. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this application to help readers better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for the convenience of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0051] To facilitate understanding of the embodiments of this application, relevant content regarding the logging system will be introduced first.

[0052] Well logging is one of the important technologies in the field of exploration, and it plays a very important role in the process of oil and gas exploration and development.

[0053] In current logging systems, acoustic and sensor combinations are commonly used to acquire logging data in simple sandstone and mudstone formations. Common logging parameters include natural gamma, wellbore inclination azimuth, spontaneous potential, compensated acoustic logging, dual-induction eight-lateral logging, wellbore diameter, microelectrode, and formation gradient resistivity (e.g., gradient resistivity of a 4-meter formation). However, some logging systems (such as the SL6000 logging system) do not include formation gradient resistivity measurement in their acoustic and sensor combinations. To measure the formation gradient resistivity curve, a separate electrode sub needs to be designed and manufactured and attached to the instrument string. This not only increases costs but also lengthens the instrument string, increasing operational risks and the number of connection points, leading to more potential failure points. Therefore, this method of measuring formation gradient resistivity by separately manufacturing an electrode sub is ineffective.

[0054] Example 1:

[0055] The embodiments of this application relate to a gradient resistivity measurement system.

[0056] Compared with the prior art, the implementation method of this application uses the electrode assembly on the bridle and the original mud resistivity plate mounting position in the telemetry instrument to detachably install the gradient resistivity plate. The gradient resistivity plate and the electrode assembly electrically connected to it are used to measure the gradient resistivity of the formation. The measurement results of the gradient resistivity are transmitted to the surface system through the data transmission device corresponding to the mud resistivity plate. Since the bridle and the telemetry instrument are existing structures on the instrument string, the impact on the length of the instrument string and the number of connection points is reduced, and the cost is also reduced. The gradient resistivity of the formation and other logging items in the instrument string can be completed in one well run. Therefore, the problem of poor performance of the method of measuring the gradient resistivity of the formation by separately manufacturing electrode subs is solved.

[0057] The following is a detailed description of the implementation details of the gradient resistivity measurement system in this embodiment. The following content is only for the convenience of understanding and is not necessary for implementing this solution.

[0058] This embodiment provides a gradient resistivity measurement system, such as Figure 1 As shown, it includes:

[0059] The instrument string 100 includes a bridle 200 and a telemetry instrument 300. The bridle 200 has an electrode assembly 210, and the telemetry instrument 300 includes a mud resistivity plate mounting position 310 and a corresponding data transmission device 320.

[0060] The gradient resistivity plate 400 is detachably installed in the mounting position 310 when the mud resistivity plate is not installed, and is electrically connected to the electrode assembly 210 and the data transmission device 320 respectively. It is used to measure the gradient resistivity of the formation through the electrode assembly 210 and send the measurement result of the gradient resistivity to the data transmission device 320. The data transmission device 320 is used to transmit the measurement result of the gradient resistivity to the ground system 500.

[0061] In practice, the logging system includes a surface system and an instrument string, which contains logging instruments with different functions. Lowering the instrument string into the well allows multiple logging tasks to be completed in a single run, eliminating the need for multiple runs and improving logging efficiency. For example, the logging system could be the SL6000 logging system.

[0062] In practical applications, the demand for measuring formation gradient resistivity is increasing. However, some logging systems are not designed to measure formation gradient resistivity. To achieve the measurement of all logging items, including formation gradient resistivity, in a single downhole run, this embodiment provides a new gradient resistivity measurement system that improves upon the existing instrument string structure without requiring the separate design and fabrication of electrode subs. The existing instrument string structure includes a bridle for connecting the cable and the instrument, and a telemetry instrument with a mud resistivity plate. The mud resistivity plate is a circuit board for measuring mud resistivity. The inventors discovered that mud resistivity measurement does not necessarily have to be performed downhole; it can be measured after the instrument string is brought out of the well by collecting the mud carried on the instrument string and using a dedicated mud resistivity measuring instrument. Based on this, the inventors designed a novel gradient resistivity plate, specifically a circuit board for measuring gradient resistivity, using a bridle with electrode components. When it is necessary to measure the gradient resistivity of a formation, the mud resistivity plate can be replaced with the gradient resistivity plate. The gradient resistivity of the formation is measured through the electrode components on the bridle, and the measured gradient resistivity is transmitted to the surface system using the existing data transmission device of the mud resistivity plate. The surface system decodes the received digital signal carrying the gradient resistivity to obtain and record the gradient resistivity. This allows for the completion of formation gradient resistivity and all other logging items (such as the acquisition of all conventional curves in acoustic and sensor combinations) in a single well run. This approach does not increase the length of the original instrument string, reducing the labor intensity of the operators, lowering the risk of accidents such as obstruction or jamming during well runs, and reducing potential failure points by eliminating additional connection points.

[0063] The gradient resistivity plate can be connected to the existing power supply terminal of the mud resistivity plate. The data transmission device communicates with the ground system.

[0064] Depending on the construction requirements of different work areas, the gradient resistivity of the strata can be measured at different depths. For example, the gradient resistivity of a 4-meter stratum, a 2.5-meter stratum, or a 0.45-meter stratum can be measured. Gradient resistivity measurements at different depths require a bridle with corresponding electrode components, which can be configured according to actual needs.

[0065] The gradient resistivity plate can be detachably installed at the mounting position of the mud resistivity plate. When it is not necessary to measure the gradient resistivity of the formation, the gradient resistivity plate can be removed and the mud resistivity plate can be installed back without affecting the use of the mud resistivity plate.

[0066] For example, the telemetry instrument could be the SL6514 high-speed digital telemetry system. The data transmission device in the telemetry instrument includes an analog-to-digital converter (ADC) and a communication board. The ADC is connected to both the gradient resistivity plate and the communication board, and is used to convert the measurement results of the formation's gradient resistivity into digital data before sending them to the communication board for transmission to the ground system.

[0067] In this embodiment, the gradient resistivity plate is detachably installed using the electrode assembly on the bridle and the mounting position of the existing mud resistivity plate in the telemetry instrument. The gradient resistivity plate and the electrode assembly electrically connected to it are used to measure the gradient resistivity of the formation. The measurement results are transmitted to the surface system through the data transmission device corresponding to the mud resistivity plate. Since the bridle and the telemetry instrument are existing structures on the instrument string, the impact on the length of the instrument string and the number of connection points is reduced, and the cost is also reduced. The gradient resistivity of the formation and other logging items in the instrument string can be completed in one well run. Therefore, the problem of poor performance of the method of measuring the gradient resistivity of the formation by separately manufacturing electrode subs is solved.

[0068] Example 2:

[0069] The implementation method of this application is a detailed description of the gradient resistivity plate 400 described above, such as... Figure 2 As shown, the gradient resistivity plate 400 includes a waveform generator 410, a shaping circuit 420, a constant current source circuit 430, a measurement circuit 440, and a rectifier and filter circuit 450.

[0070] Among them, waveform generator 410 is used to generate waveform signals and output them;

[0071] The shaping circuit 420 is connected to the waveform generator 410 and is used to shape the waveform signal to obtain a control signal, and then provide the control signal to the rectifier and filter circuit 450.

[0072] The constant current source circuit 430 is connected to the waveform generator 410 and the measurement circuit 440 respectively, and is used to generate a constant current signal based on the waveform signal as a power supply signal, and to provide the power supply signal to the measurement circuit 440.

[0073] The measurement circuit 440 is also connected to the constant current source circuit 430, the electrode assembly 210 and the rectifier and filter circuit 450 respectively. It is used to provide the power supply signal to the formation through the electrode assembly 210 in the logging state, and to obtain the gradient resistivity measurement signal through the electrode assembly 210 and provide the measurement signal to the rectifier and filter circuit 450.

[0074] The rectifier and filter circuit 450 is also connected to the data transmission device 320. Under the control of the control signal, it rectifies and filters the measurement signal to obtain the gradient resistivity measurement result and sends the gradient resistivity measurement result to the data transmission device 320.

[0075] The waveform signal can be a square wave signal. Correspondingly, the power supply signal, control signal, and measurement signal are also square wave signals. Square wave signals have stronger anti-interference capabilities, making the gradient resistivity measurement results more accurate.

[0076] In this embodiment, based on the waveform signal generated by the waveform generator 410, the shaping circuit 420 can obtain a control signal, and the constant current source circuit 430 can generate a power supply signal of the same frequency to provide to the electrode assembly 210. This allows the electrode assembly 210 to obtain a gradient resistivity measurement signal. Under the control of the aforementioned control signal, the measurement signal of the electrode assembly 210 is rectified and filtered by the rectifier and filter circuit 450, resulting in a more accurate gradient resistivity measurement result.

[0077] In some examples, such as Figure 3 and Figure 4 As shown, the electrode assembly 210 includes a first electrode ring M1, a second electrode ring M2, a third electrode ring A, and a torpedo B;

[0078] The first input terminal of the measurement circuit 440 is connected to the first electrode ring M1, the second input terminal is connected to the second electrode ring M2, the third input terminal is connected to the torpedo B, the fourth input terminal is connected to the output terminal of the constant current source circuit 430, the first output terminal is connected to the first input terminal RM of the rectifier filter circuit 450, the second output terminal is connected to the second input terminal RN of the rectifier filter circuit 450, and the third output terminal is connected to the third electrode ring A. It is used to provide the power supply signal to the formation through the third electrode ring A in the logging state, and to provide the signals of the first electrode ring M1 and the second electrode ring M2 to the rectifier filter circuit 450. The measurement signal includes the signals of the first electrode ring M1 and the second electrode ring M2.

[0079] The third input terminal of the measurement circuit 440 is also grounded.

[0080] For example, such as Figure 3 As shown, the electrode assembly 210 includes an electrode body 211 with a preset length. A first electrode ring M1, a second electrode ring M2, and a third electrode ring A are fitted onto the electrode body 211. One end of the electrode body 211 is located on the bridle 200, and the other end is connected to the torpedo B. Therefore, the torpedo B is equivalent to the fourth electrode ring of the electrode assembly 210. From the bridle 200 to the torpedo B, the second electrode ring M2, the first electrode ring M1, the natural potential SP, and the third electrode ring A are sequentially arranged.

[0081] The preset length can be set according to actual needs. Figure 3 The lengths between B and A, A and SP, SP and M1, M1 and M2, and M2 and the horse bridle 200 are shown in the diagram in sequence as 5.6 meters (m), 1 meter, 2.75 meters, 0.5 meters, and 4 meters.

[0082] The bridle has multiple cable cores. The telemetry instrument has multiple cable cores. The electrode assembly is electrically connected to the gradient resistivity plate via the cable cores of the bridle and the telemetry instrument. For example, the natural potential SP is connected to a 7-core cable, and the natural potential signal of the natural potential SP is transmitted to the ground system 500 via the 7-core cable, disconnecting from the 7# cable core of the bridle. The third electrode ring A is connected to the 7# cable core of the bridle, the first electrode ring M1 is connected to the 8# cable core of the bridle, the second electrode ring M2 is connected to the 9# cable core of the bridle, and the torpedo B is connected to the 10# cable core of the bridle. 7# to 10# are cable core numbers.

[0083] If the telemetry instrument is an SL6514 high-speed digital telemetry system, the upper part of the telemetry instrument includes cable cores #22, #23, #24, and #25. When the electrode assembly is connected to the gradient resistivity plate 400 via the bridle and the telemetry instrument, cable cores #7 and #22 are short-circuited, #8 and #23 are short-circuited, #9 and #24 are short-circuited, and #10 and #25 are short-circuited. The gradient resistivity plate 400 is powered through cable cores #22 and #25, and receives signals from the first electrode ring M1 and the second electrode ring M2 through cable cores #23 and #24. Here, #22 to #25 are cable core numbers.

[0084] In this embodiment, after the measurement circuit 440 provides a power supply signal to the formation through the third electrode ring A, the third electrode ring A, the formation, and the torpedo B constitute a power supply loop. The gradient resistivity of the formation can be measured through the first electrode ring M1 and the second electrode ring M2. Thus, the gradient resistivity of the formation can be measured using the simple structure of the electrode assembly 210, making it more practical.

[0085] In some examples, such as Figure 4 As shown, the measurement circuit 440 includes a first resistor R1, a second resistor R2, a third resistor R3, a first switching switch S1, a second switching switch S2, and a third switching switch S3.

[0086] The fourth input terminal of the measurement circuit 440 is connected to the first terminal of the first resistor R1 and the third output terminal of the measurement circuit 440 respectively through the first switching switch S1.

[0087] The second end of the first resistor R1 is connected to the first end of the second resistor R2, and is also connected to the first input end and the first output end of the measurement circuit 440 respectively through the second switching switch S2.

[0088] The second end of the second resistor R2 is connected to the first end of the third resistor R3, and is also connected to the second input end and the second output end of the measurement circuit 440 through the third switching switch S3.

[0089] The second terminal of the third resistor R3 is grounded;

[0090] The first switching switch S1, the second switching switch S2, and the third switching switch S3 are used to connect the first end of the first resistor R1 to the fourth input terminal of the measurement circuit 440, the second end of the first resistor R1 to the first output terminal of the measurement circuit 440, and the second end of the second resistor R2 to the second output terminal of the measurement circuit 440 when switching to the test state, so as to test the reference value of the gradient resistivity measurement result obtained by the rectifier filter circuit 450; when switching to the logging state, they connect the fourth input terminal and the third output terminal, the first input terminal and the first output terminal, and the second input terminal and the second output terminal of the measurement circuit 440, so as to measure the gradient resistivity downhole.

[0091] In practice, the gradient resistivity measurement system can be tested first to obtain a reference value for the gradient resistivity measurement result obtained from the rectifier and filter circuit. During actual well logging, the actual gradient resistivity measurement result can be compared with the reference value to determine whether the measurement is normal.

[0092] Among them, the first switching switch S1, the second switching switch S2 and the third switching switch S3 can be single-pole double-throw switches, which can switch between test state and logging state.

[0093] When the first switch S1, the second switch S2, and the third switch S3 are all switched to the test position, the test state is entered. (See below) Figure 4 As shown, the first terminal of the first resistor R1 is connected to the fourth input terminal of the measurement circuit 440, the second terminal of the first resistor R1 is connected to the first output terminal of the measurement circuit 440, and the second terminal of the second resistor R2 is connected to the second output terminal of the measurement circuit 440. The power supply signal input to the fourth input terminal of the measurement circuit 440 passes through the three resistors R1, R2, and R3. The first and second output terminals of the measurement circuit 440 are respectively connected to the two ends of the second resistor R2. The signals from the first and second output terminals of the measurement circuit 440 characterize the voltage across the second resistor R2. The signals from the first and second output terminals of the measurement circuit 440 enter the rectifier and filter circuit 450, causing the rectifier and filter circuit 450 to output the voltage of the second resistor R2. This voltage serves as a reference value for the gradient resistivity measurement result, i.e., the calibration voltage. For example, when measuring the gradient resistivity of a 4-meter stratum, the voltage of the second resistor R2 is 1840 mV, representing a 200 ohm-meter stratum.

[0094] When the first switching switch S1, the second switching switch S2, and the third switching switch S3 are switched to the logging position, the logging state is entered. The fourth input terminal and the third output terminal of the measurement circuit 440, the first input terminal and the first output terminal of the measurement circuit 440, and the second input terminal and the second output terminal of the measurement circuit 440 are connected. The power supply signal input from the fourth input terminal of the measurement circuit 440 enters the formation through the third electrode ring A and then returns to the torpedo B. The signals from the first electrode ring M1 and the second electrode ring M2 enter the measurement circuit 440. The measurement circuit 440 provides the signals from the first electrode ring M1 and the second electrode ring M2 to the rectifier and filter circuit 450, so that the rectifier and filter circuit 450 outputs the gradient resistivity Rm of the downhole formation.

[0095] The measurement circuit 440 in this embodiment can not only obtain reference values ​​of gradient resistivity measurement results through internal resistance testing to provide a reference for actual logging, but also realize actual logging control. In this way, the switching between testing and logging is realized by using a common circuit structure, which simplifies the circuit structure.

[0096] In some examples, such as Figure 4 As shown, the rectifier-filter circuit 450 includes a first amplifier circuit 451, a rectifier circuit 452, and a filter circuit 453.

[0097] The first amplifier circuit 451 is connected to the measurement circuit 440 and the rectifier circuit 452 respectively, and is used to amplify the measurement signal to obtain the first amplified signal, and provide the first amplified signal to the rectifier circuit 452.

[0098] The rectifier circuit 452 is also connected to the shaping circuit 420 and the filter circuit 453 respectively, and is used to rectify the first amplified signal to obtain the first DC signal under the control of the control signal, and provide the first DC signal to the filter circuit 453.

[0099] The filter circuit 453 is also connected to the data transmission device 320 and is used to filter the first DC signal to obtain a second DC signal, which is the measurement result of gradient resistivity; and to send the second DC signal to the data transmission device 320.

[0100] In some examples, such as Figure 4 As shown, the first amplifier circuit 451 may specifically include: a first amplifier U1 and a second amplifier U2.

[0101] In this amplifier, the non-inverting input of the first amplifier U1 is connected to the first input of the rectifier-filter circuit 450 via the fourth resistor R4 and grounded via the fifth resistor R5. The inverting input is connected to the second input of the rectifier-filter circuit 450 via the sixth resistor R6 and to the output of the first amplifier U1 via the seventh resistor R7. The output is also connected to the inverting output of the second amplifier U2 via the eighth resistor R8. The first amplifier U1 uses its own output feedback signal, along with the signals from the first electrode ring M1 and the second electrode ring M2, to differentially amplify the signals from the first electrode ring M1 and the second electrode ring M2 to obtain a differential amplified signal, which is then output to the second amplifier U2. This eliminates common-mode interference. The first amplifier U1 may include an OP37 operational amplifier.

[0102] The non-inverting input of the second amplifier U2 is grounded through the ninth resistor R9, and the inverting input is connected to the output of the second amplifier U2 through the tenth resistor R10. The output is connected to the output of the first amplifier circuit 451. The output of the first amplifier circuit 451 is connected to the first input of the rectifier circuit 452. The second amplifier U2 is used to invert the differential amplified signal and the feedback signal from its own output to obtain an inverted amplified signal, which is then output as the first amplified signal to the rectifier circuit 452. The second amplifier U2 may include an LM741 operational amplifier.

[0103] For example, the amplification factor of the first amplifier U1 is 10 times, and the amplification factor of the second amplifier U2 is 5 times.

[0104] In some examples, such as Figure 4 As shown, the rectifier circuit 452 may specifically include: a first capacitor C1, a second capacitor C2, a transformer T, an analog switch integrated circuit U6, an eleventh resistor R11, and a twelfth resistor R12. The first capacitor C1 and the second capacitor C2 are polarized capacitors. The transformer T is an isolation phase-sensitive detector transformer. The analog switch integrated circuit U6 may include a DG307 analog switch integrated circuit.

[0105] The negative terminal of the first capacitor C1 is connected to the first input terminal of the rectifier circuit 452, and the positive terminal is connected to the positive terminal of the second capacitor C2.

[0106] The negative terminal of the second capacitor C2 is connected to the first input terminal of the primary side of the transformer T.

[0107] The second input terminal of the primary side of transformer T is grounded. The first output terminal of the secondary side of transformer T is connected to the common terminal of the first analog switch in analog switch integrated circuit U6, the second output terminal is grounded, and the third output terminal is connected to the negative power supply pin of analog switch integrated circuit U6. Transformer T is used to transform the voltage of the first amplified signal after passing through the first capacitor C1 and the second capacitor C2 to obtain the first AC current, which is then supplied to analog switch integrated circuit U6.

[0108] In analog switch integrated circuit U6, the positive power supply pin and the common terminal of the second analog switch are connected to the second input terminal of rectifier circuit 452. The second input terminal of rectifier circuit 452 is connected to the output terminal of shaping circuit 420. The normally open and normally closed contacts of the first analog switch in analog switch integrated circuit U6 are connected to the output terminal of rectifier circuit 452 through eleventh resistor R11. The output terminal of rectifier circuit 452 is connected to the input terminal of filter circuit 453. The first end of twelfth resistor R12 is connected to the output terminal of rectifier circuit 452, and the second end is grounded.

[0109] The analog switch integrated circuit U6 is used to rectify the first AC power under the control of the control signal K to obtain the first DC signal, and then provide the first DC signal to the filter circuit 453.

[0110] In practice, the first amplified signal passes through an isolation phase-sensitive detector transformer and then enters the analog switch integrated circuit U6. Under the control of the control signal K, it is converted into a first DC signal and output to the filter circuit 453.

[0111] The filter circuit 453 may specifically include a third capacitor C3 and a fourth capacitor C4. The third capacitor C3 is a polarized capacitor.

[0112] The input terminal of the filter circuit 453 is also connected to the positive terminal of the third capacitor C3, the first terminal of the fourth capacitor C4, and the output terminal of the filter circuit 453, respectively. The negative terminal of the third capacitor C3 and the second terminal of the fourth capacitor C4 are grounded.

[0113] Thus, filtering the first DC signal through the filter circuit 453 results in a better quality second DC signal, improving the accuracy of the measured gradient resistivity.

[0114] In this embodiment, the signals of the first electrode ring M1 and the second electrode ring M2 are amplified by the rectifier and filter circuit 450 and then rectified and filtered, so that the final gradient resistivity measurement result signal is enhanced and the measurement is more accurate.

[0115] In some embodiments, such as Figure 4 As shown, the shaping circuit 420 includes a resistor unit 421, a first inverting circuit 422, and a second inverting circuit 423;

[0116] The first inverting circuit 422 is connected to the input terminal of the shaping circuit 420 through the resistor unit 421, and is also connected to the input terminal of the second inverting circuit 423. It is used to invert the waveform signal to obtain the first inverted signal and provide the first inverted signal to the second inverting circuit 423.

[0117] The second inverting circuit 423 is also connected to the output terminal of the shaping circuit 420, and is used to invert the first inverting signal to obtain the second inverting signal, and provide the second inverting signal as a control signal to the rectifier filter circuit 450.

[0118] Among them, resistor unit 421 includes the thirteenth resistor R13.

[0119] The first inverter circuit 422 includes a first inverter U11, and the second inverter circuit 423 includes a second inverter U12.

[0120] Both the first inverter U11 and the second inverter U12 can be CD40106. CD40106 is an inverter integrated circuit with Schmitt triggering characteristics.

[0121] In this embodiment, the waveform signal that has been stepped down by the resistor unit 421 is inverted twice by the first inverting circuit 422 and the second inverting circuit 423, thereby achieving shaping. This makes the shaped control signal waveform more standard.

[0122] In some embodiments, such as Figure 4 As shown, the constant current source circuit 430 includes a second amplifier circuit 431, a third amplifier circuit 432, and a fourth amplifier circuit 433;

[0123] The second amplifier circuit 431 is connected to the waveform generator 410, the third amplifier circuit 432 and the fourth amplifier circuit 433 respectively. It is used to differentially amplify the waveform signal and the third amplified signal from the third amplifier circuit 432 to obtain the second amplified signal, and to provide the second amplified signal to the fourth amplifier circuit 433.

[0124] The fourth amplifier circuit 433 is also connected to the measurement circuit 440, and is used to amplify the second amplified signal to obtain the fourth amplified signal, obtain the power supply signal based on the fourth amplified signal, and provide the power supply signal to the measurement circuit 440.

[0125] The third amplifier circuit 432 is also connected to the fourth amplifier circuit 433, which amplifies the fourth amplified signal to obtain the third amplified signal, and provides the third amplified signal to the second amplifier circuit 431 so that the fourth amplified signal is a constant current signal.

[0126] Specifically, the second amplifier circuit 431 includes a third amplifier U3. The non-inverting input terminal of the third amplifier U3 is connected to the first input terminal of the second amplifier circuit 431 through the fourteenth resistor R14, the common terminal and the first fixed terminal of the potentiometer RP, and the fifteenth resistor R15. The first input terminal of the second amplifier circuit 431 is connected to the input terminal of the constant current source circuit 430. The input terminal of the constant current source circuit 430 is connected to the output terminal of the waveform generator 410.

[0127] The output of the third amplifier U3 is connected to the output of the second amplifier circuit 431. The output of the second amplifier circuit 431 is connected to the input of the fourth amplifier circuit 433.

[0128] The inverting input of the third amplifier U3 is connected to the second input of the second amplifier circuit 431. The second input of the second amplifier circuit 431 is connected to the output of the third amplifier circuit 432.

[0129] The third amplifier U3 can be an LM741 operational amplifier. The second fixed terminal of potentiometer RP is grounded. Potentiometer RP can be a high-temperature potentiometer.

[0130] The fourth amplifier circuit 433 includes a fourth amplifier U4. The input terminal of the fourth amplifier U4 is connected to the input terminal of the fourth amplifier circuit 433, and its output terminal is connected to the output terminal of the fourth amplifier circuit 433. The output terminal of the fourth amplifier circuit 433 is connected to the first terminal of the sixteenth resistor R16. The second terminal of the sixteenth resistor R16 is connected to the output terminal of the constant current source circuit 430. The output terminal of the constant current source circuit 430 is connected to the fourth input terminal of the measurement circuit 440. The fourth amplifier U4 can be an LH823 power amplifier.

[0131] The third amplifier circuit 432 includes a fifth amplifier U5. The inverting input of the fifth amplifier U5 is connected to the output of the fourth amplifier U4 through the seventeenth resistor R17. The non-inverting input is connected to the second terminal of the sixteenth resistor R16 through the eighteenth resistor R18 and grounded through the nineteenth resistor R19. The output is connected to the output of the third amplifier circuit 432 through the twentieth resistor R20 and to the inverting input of the fifth amplifier U5 through the twenty-first resistor R21. The fifth amplifier U5 can be an OP37 operational amplifier. The first terminal of the sixteenth resistor R16 serves as the first input of the third amplifier circuit 432. The second terminal of the sixteenth resistor R16 serves as the second input of the third amplifier circuit 432.

[0132] For example, in the constant current source circuit 430, the fourth amplifier U4 can output a stable constant current signal at the output terminal E0, and the current of the constant current signal is 100±5 mA.

[0133] In this embodiment, the waveform signal can be amplified by the second amplifier circuit 431 and the fourth amplifier circuit 433. Then, the output after being amplified by the second amplifier circuit 431 and the fourth amplifier circuit 433 is further amplified by the third amplifier circuit 432 and monitored by constant current, which can make the constant current signal used as the power supply signal more stable.

[0134] In some embodiments, such as Figure 4 As shown, the waveform generator 410 includes an oscillation circuit 411, a frequency divider circuit 412, and a comparator circuit 413;

[0135] The oscillation circuit 411 is connected to the frequency divider circuit 412 and is used to generate an oscillation signal and provide the oscillation signal to the frequency divider circuit 412.

[0136] The frequency divider circuit 412 is also connected to the comparator circuit 413, which is used to divide the oscillation signal to obtain the first square wave signal and provide the first square wave signal to the comparator circuit 413.

[0137] The comparator circuit 413 is also connected to the shaping circuit 420 and the constant current source circuit 430 respectively, and is used to compare the first square wave signal with its own output feedback signal to obtain the second square wave signal, which is a waveform signal; and to provide the second square wave signal to the shaping circuit 420 and the constant current source circuit 430.

[0138] Specifically, such as Figure 4 As shown, the oscillation circuit 411 includes a fifth capacitor C5, a twenty-second resistor R22, a third inverter U13, and a fourth inverter U14. The input terminal of the third inverter U13 is connected to the first terminal of the fifth capacitor C5 and the first terminal of the twenty-second resistor R22, respectively. Its output terminal is connected to the second terminal of the twenty-second resistor R22 and the input terminal of the fourth inverter U14, respectively. The output terminal of the fourth inverter U14 is connected to the output terminal of the oscillation circuit 411. The output terminal of the oscillation circuit 411 is connected to the input terminal of the frequency divider circuit 412. The third inverter U13 and the fourth inverter U14 can be CD40106.

[0139] An oscillation signal can be generated by the combination of the fifth capacitor C5, the twenty-second resistor R22, the third inverter U13, and the fourth inverter U14.

[0140] The frequency divider circuit 412 may include a frequency divider counter U0. For example, the frequency divider counter U0 may be a CD4040 counter.

[0141] The clock pulse input pin CLK of the frequency divider counter U0 is connected to the input of the frequency divider circuit 412, the reset pin RST is grounded, and the counting output Q2 is connected to the output of the frequency divider circuit 412. The output of the frequency divider circuit 412 is connected to the input of the comparator circuit 413.

[0142] The comparator circuit 413 includes a comparator U. The non-inverting input terminal of the comparator U is connected to the input terminal of the comparator circuit 413 through the twenty-third resistor R23, the inverting input terminal is grounded through the twenty-fourth resistor R24 ​​and connected to the positive power supply pin through the twenty-fifth resistor R25, and the output terminal is connected to the output terminal of the comparator circuit 413.

[0143] For example, the output of the comparator circuit 413 can output a square wave signal of 25±3HZ.

[0144] In the waveform generator 410 of this embodiment, the square wave signal after frequency division of the oscillation signal is further adjusted by the comparison circuit 413 to make the square wave signal more standard.

[0145] Example 3:

[0146] The gradient resistivity measurement system provided in this embodiment will be described in more detail below, taking the gradient resistivity measurement of a 4-meter stratum as an example.

[0147] In this embodiment, logging is performed based on the SL6000 logging system. Within the logging system, the surface system is connected via cable to a bridle containing electrode components within the instrument string. The bridle is connected to an SL6514 high-speed digital telemetry instrument within the instrument string. The SL6514 high-speed digital telemetry instrument is equipped with… Figure 5 The gradient resistivity plate shown is 400. The surface system supplies 180V AC power to the downhole instrument and preheats it for 30 minutes. Checking the gradient resistivity values ​​via the surface system reveals they are not 0 or negative, indicating normal signal transmission of the 4-meter formation gradient resistivity measurement results. Calibration is performed; if the calibration error is within the allowable range, the instrument is functioning correctly and can be used for well logging.

[0148] When performing calibration, it can be achieved using an external calibration resistor network, such as... Figure 6 As shown, the external scale resistor network includes a 26th resistor R26, a 27th resistor R27, and a 28th resistor R28 connected in series. The 26th resistor R26 is located between the first node P1 and the second node P2, the 27th resistor R27 is located between the second node P2 and the third node P3, and the 28th resistor R28 is located between the third node P3 and the fourth node P4.

[0149] The first node P1 connects to the third electrode ring A, the second node P2 connects to the first electrode ring M1, the third node P3 connects to the second electrode ring M2, and the fourth node P4 connects to the outer shell of torpedo B. Check the measurement results to verify the accuracy of the gradient resistivity curve for the 4-meter stratum. For example, the scale voltage for the gradient resistivity of the 4-meter stratum is 1.84V, corresponding to 200 ohm-meters.

[0150] Change the mud resistivity scale factor in the well logging service table to the gradient resistivity scale factor of the 4-meter formation.

[0151] During on-site testing, such as ​ As shown, based on the SL6000 logging system, the instrument string includes an acoustic and sensor combination comprising a dual-sensor eight-lateral instrument, a microelectrode and caliper instrument, a 3516 encoding instrument (an instrument used to encode information according to a predetermined format), a high-speed digital acoustic instrument, a cross-sectional instrument, a telemetry instrument, a three-parameter instrument, and a bridle. The logging winch lowers the instrument string to the designated depth in the well via a cable. Following the operating procedures in the SL6000 instrument operation manual, power is supplied to the SL6000 downhole instrument string. Scale sampling and data storage are performed according to the operating procedures in the SL6000 instrument operation manual. The cable is then pulled back to measure the repeat curve and the master curve. The accuracy of the gradient resistivity curve for the 4-meter formation is verified. Comparing the gradient resistivity curve of the 4-meter formation with other curves, the measurements for pure mudstone are almost identical, showing a good correlation with other curves.

[0152] Example 4:

[0153] The embodiments of this application also provide an instrument string, including the gradient resistivity measurement system as described in the above embodiments. In this embodiment, the gradient resistivity plate is detachably installed using the electrode assembly on the bridle and the mounting position of the existing mud resistivity plate in the telemetry instrument. The gradient resistivity of the formation is measured through the gradient resistivity plate and the electrode assembly electrically connected to it, and the measurement result is transmitted to the surface system through the data transmission device corresponding to the mud resistivity plate. Since the bridle and the telemetry instrument are existing structures on the instrument string, the impact on the length of the instrument string and the number of connection points is reduced, and the cost is also reduced. The gradient resistivity of the formation and other logging items in the instrument string can be completed in one well run, thus solving the problem of poor performance of the method of measuring the gradient resistivity of the formation by separately manufacturing electrode subs.

[0154] Example 5:

[0155] This application also provides a logging system, including a surface system and an instrument string as described in the above embodiments. In this embodiment, an electrode assembly on the bridle is used, and the existing mud resistivity plate mounting position in the telemetry instrument is used to detachably install a gradient resistivity plate. The gradient resistivity plate and the electrode assembly electrically connected to it are used to measure the gradient resistivity of the formation. The measurement results of the gradient resistivity are transmitted to the surface system through the data transmission device corresponding to the mud resistivity plate. Since the bridle and the telemetry instrument are existing structures on the instrument string, the impact on the length of the instrument string and the number of connection points is reduced, and the cost is also reduced. The gradient resistivity of the formation and other logging items in the instrument string can be completed in one well run, thus solving the problem that the method of measuring the gradient resistivity of the formation by separately manufacturing electrode subs is not effective.

[0156] It should be understood that the terms "mechanism," "device," "component," etc., used in this application are merely one method of distinguishing different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they can be replaced by other expressions.

[0157] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application. In practical applications, the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification, and various changes can be made to them in form and detail without departing from the spirit and scope of this application.

Claims

1. A gradient resistivity measurement system, characterized in that, include: The instrument string includes a bridle and a telemeter, the bridle having an electrode assembly and the telemeter including a mounting position for a mud resistivity plate and a corresponding data transmission device. A gradient resistivity plate, wherein the gradient resistivity plate is detachably installed at the mounting position when the mud resistivity plate is not installed, and is electrically connected to the electrode assembly and the data transmission device respectively, for measuring the gradient resistivity of the formation through the electrode assembly and sending the measurement result of the gradient resistivity to the data transmission device; the data transmission device is used to transmit the measurement result of the gradient resistivity to the ground system.

2. The gradient resistivity measurement system according to claim 1, characterized in that, The gradient resistivity plate includes a waveform generator, a shaping circuit, a constant current source circuit, a measurement circuit, and a rectification and filtering circuit. The waveform generator is used to generate and output waveform signals. The shaping circuit is connected to the waveform generator and is used to shape the waveform signal to obtain a control signal, and to provide the control signal to the rectifier and filter circuit. The constant current source circuit is connected to the waveform generator and the measurement circuit respectively, and is used to generate a constant current signal based on the waveform signal as a power supply signal, and to provide the power supply signal to the measurement circuit. The measurement circuit is also connected to the constant current source circuit, the electrode assembly, and the rectifier filter circuit, respectively, and is used to provide the power supply signal to the formation through the electrode assembly in the logging state, obtain the gradient resistivity measurement signal through the electrode assembly, and provide the measurement signal to the rectifier filter circuit. The rectifier and filter circuit is also connected to the data transmission device, and is used to rectify and filter the measurement signal under the control of the control signal to obtain the measurement result of the gradient resistivity, and send the measurement result of the gradient resistivity to the data transmission device.

3. The gradient resistivity measurement system according to claim 2, characterized in that, The rectifier-filter circuit includes a first amplifier circuit, a rectifier circuit, and a filter circuit; The first amplifier circuit is connected to the measurement circuit and the rectifier circuit respectively, and is used to amplify the measurement signal to obtain a first amplified signal, and provide the first amplified signal to the rectifier circuit. The rectifier circuit is also connected to the shaping circuit and the filter circuit respectively, and is used to rectify the first amplified signal to obtain a first DC signal under the control of the control signal, and provide the first DC signal to the filter circuit. The filtering circuit is also connected to the data transmission device and is used to filter the first DC signal to obtain a second DC signal, the second DC signal being the measurement result of the gradient resistivity; and to send the second DC signal to the data transmission device.

4. The gradient resistivity measurement system according to claim 2, characterized in that, The electrode assembly includes a first electrode ring, a second electrode ring, a third electrode ring, and a torpedo; The first input terminal of the measurement circuit is connected to the first electrode ring, the second input terminal is connected to the second electrode ring, the third input terminal is connected to the torpedo, the fourth input terminal is connected to the output terminal of the constant current source circuit, the first output terminal is connected to the first input terminal of the rectifier and filter circuit, the second output terminal is connected to the second input terminal of the rectifier and filter circuit, and the third output terminal is connected to the third electrode ring. This circuit, in logging mode, provides the power supply signal to the formation through the third electrode ring and provides the signals from the first and second electrode rings to the rectifier and filter circuit. The measurement signal includes the signals from the first and second electrode rings. The third input terminal of the measurement circuit is also grounded.

5. The gradient resistivity measurement system according to claim 4, characterized in that, The measurement circuit includes a first resistor, a second resistor, a third resistor, a first switch, a second switch, and a third switch; The fourth input terminal of the measurement circuit is connected to the first terminal of the first resistor and the third output terminal of the measurement circuit respectively through the first switching switch. The second end of the first resistor is connected to the first end of the second resistor, and is also connected to the first input end and the first output end of the measurement circuit respectively through the second switching switch; The second end of the second resistor is connected to the first end of the third resistor, and is also connected to the second input end and the second output end of the measurement circuit through the third switching switch; The second terminal of the third resistor is grounded; The first switch, the second switch, and the third switch are used to connect the first end of the first resistor to the fourth input terminal of the measurement circuit, the second end of the first resistor to the first output terminal of the measurement circuit, and the second end of the second resistor to the second output terminal of the measurement circuit when switching to the test state, so as to test the reference value of the measurement result of the gradient resistivity obtained by the rectifier filter circuit. When switching to logging mode, conduction is made between the fourth input terminal and the third output terminal of the measurement circuit, between the first input terminal and the first output terminal of the measurement circuit, and between the second input terminal and the second output terminal of the measurement circuit, so as to measure the gradient resistivity downhole.

6. The gradient resistivity measurement system according to claim 2, characterized in that, The shaping circuit includes a resistor unit, a first inverting circuit, and a second inverting circuit; The first inverting circuit is connected to the waveform generator through the resistor unit and also to the second inverting circuit. It is used to invert the waveform signal to obtain a first inverted signal and provide the first inverted signal to the second inverting circuit. The second inverting circuit is also connected to the rectifier-filter circuit, and is used to invert the first inverted signal to obtain a second inverted signal, and provide the second inverted signal as the control signal to the rectifier-filter circuit.

7. The gradient resistivity measurement system according to claim 2, characterized in that, The constant current source circuit includes a second amplifier circuit, a third amplifier circuit, and a fourth amplifier circuit; The second amplifier circuit is connected to the waveform generator, the third amplifier circuit, and the fourth amplifier circuit respectively, and is used to differentially amplify the waveform signal and the third amplified signal from the third amplifier circuit to obtain the second amplified signal, and provide the second amplified signal to the fourth amplifier circuit. The fourth amplifier circuit is also connected to the measurement circuit, and is used to amplify the power of the second amplified signal to obtain the fourth amplified signal, obtain the power supply signal based on the fourth amplified signal, and provide the power supply signal to the measurement circuit. The third amplification circuit is also connected to the fourth amplification circuit, and is used to amplify the fourth amplification signal to obtain the third amplification signal, and provide the third amplification signal to the second amplification circuit so that the fourth amplification signal is a constant current signal.

8. The gradient resistivity measurement system according to claim 2, characterized in that, The waveform generator includes an oscillation circuit, a frequency divider circuit, and a comparator circuit; The oscillation circuit is connected to the frequency divider circuit and is used to generate an oscillation signal and provide the oscillation signal to the frequency divider circuit. The frequency division circuit is also connected to the comparison circuit, and is used to divide the oscillation signal to obtain a first square wave signal, and provide the first square wave signal to the comparison circuit. The comparison circuit is also connected to the shaping circuit and the constant current source circuit, respectively, and is used to compare the first square wave signal and its own output feedback signal to obtain a second square wave signal, the second square wave signal being the waveform signal; and to provide the second square wave signal to the shaping circuit and the constant current source circuit.

9. An instrument string, characterized in that, Includes the gradient resistivity measurement system as described in any one of claims 1 to 8.

10. A well logging system, characterized in that, Includes a ground system and the instrument cluster as described in claim 9.

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