Measurement sensor for borehole wall looseness of directional kilometer drill for coalbed methane drainage in mines

Abstract

The present invention provides a sensor for measuring the looseness of the borehole wall of a directional kilometer drill for coalbed methane extraction in mines. The structure includes electrodes, a stainless-steel probe tube, a main sensor circuit board, and a battery. Among them, for the stainless-steel probe tube, annular grooves with the same depth but different widths are formed on the surface for installing the electrodes. The stainless-steel outer shell of the sensor is tightly fixed to the stainless-steel probe rod through the threaded screw ports at both ends. The electrodes are fixed to the sensor housing with hollow pins, and all surfaces except the outer surface are wrapped with insulating materials. The wires are connected to the main sensor circuit board through the hollow pins. The sensor provided by the present invention can measure the looseness of the borehole wall medium in a borehole with a diameter of about 10 cm, and complete continuous measurement by the power supply of the storage battery in a borehole several kilometers long, evaluate the current state of the drill pipe and the borehole, and improve the automation level of the detection of the in-borehole state of the kilometer drill.

Description

Technical Field

[0001] The present invention relates to a measuring device for the looseness of coal seams around the borehole wall, in particular to a downhole state monitoring device for measuring the looseness of the borehole wall of a directional kilometer drill for coalbed methane extraction in mines. Background Art

[0002] The material distribution in coal seams is relatively complex, and the properties of various mineral layers directly affect the extraction of coalbed methane. By identifying the state of the borehole wall of a directional kilometer drill for coalbed methane extraction through the looseness parameter, the looseness degree of the coal seam around the borehole can be judged according to real-time data, and potential dangers such as borehole collapse and necking can be discovered in time.

[0003] The analysis of the borehole wall state, that is, the looseness, is usually based on the resistivity of the medium, and the resistivity parameters in various cases are processed to characterize the looseness degree of the borehole wall medium. Currently, there are mainly two methods for measuring the borehole wall state based on resistivity: the lateral method and the induction method. The induction method for measuring resistivity mainly relies on the change of magnetic flux in the drill pipe for measurement, and estimates the resistivity of the rock formation by combining the change of the induced potential; the lateral method directly contacts the electrode with the rock formation of the borehole wall, and calculates the resistivity of the coal seam at the location by measuring the voltage and current signals fed back by the electrode. Due to the complex nature of the minerals in the rock wall, the resistivity value ranges of different substances will overlap, and the resistivity of the same substance in different environments is also different, resulting in the need for further improvement of the borehole wall state detection technology based on resistivity.

[0004] The foreign borehole wall measurement equipment mainly uses the induction method and is mostly applied to oil well logging. In China, such as the high-resolution resistivity imaging system while drilling independently developed by the Sinopec Engineering Research Institute, it is also mainly used for oil exploration. Although the horizontal kilometer directional drill for coalbed methane extraction in mines was initially extended from the oil directional drill, its operating conditions are significantly different from those of oil drilling. The coalbed methane extraction borehole not only has a long distance and a small diameter, but also has the danger of gas outburst in the borehole. The borehole wall state measurement equipment needs to face problems such as a narrow installation space, high safety requirements, and a harsh measurement environment. Therefore, the above-mentioned borehole wall state measurement equipment can neither collect the coal and rock data around the borehole wall of the directional kilometer drill for coalbed methane extraction, nor can it be directly transplanted to the detection of the borehole wall state for coalbed methane extraction, and it also cannot meet the working conditions of coalbed methane extraction.

[0005] In the research results of measurement-while-drilling related to this patent, a measurement-while-drilling device for lateral resistivity invented by Du Haiyang et al. is applicable to formations where the mud resistivity is much lower than the resistivity of the surrounding formation, oil-based mud, and high-resistivity formations above 100 ohms; the development environment is offshore drilling development with conventional selection of saltwater mud or unconventional shale gas development, and its applicable scope and development environment are very different from coal seam drilling. In addition, in a measurement-while-drilling apparent resistivity measurement tool and method invented by Lv Haichuan et al., although this method is applicable to land drilling, further solutions are still needed for safety issues such as voltage and current levels in coal mine underground and for further excavation and utilization of the retrieved data. Therefore, this patent is a patent applicable to coal mine drilling invented for the mud types in coal mine underground, the land drilling environment, and the control and processing of current, voltage, and retrieved data, etc. Summary of the Invention

[0006] In order to solve the problems of the application of existing rock resistivity measurement instruments in coal seam drilling, as well as the problems of narrow borehole space and difficult measurement in the boreholes of coalbed methane extraction directional kilometer drills, the present invention outputs voltage signals of multiple frequencies through a CPU control circuit, and combines the looseness of the measured substance at different frequencies to realize the evaluation of the looseness of the coal and rock on the borehole wall of the coalbed methane extraction directional kilometer drill borehole.

[0007] To achieve the above object, the technical solution of the present invention is: to provide a sensor for measuring the looseness of the borehole wall of a mine-used coalbed methane extraction directional kilometer drill, and the sensor for measuring the looseness of the borehole wall of the mine-used coalbed methane extraction directional kilometer drill mainly consists of electrodes, a stainless steel probe tube, a main sensor circuit board, and a battery.

[0008] The electrodes are distributed according to the design requirements of the outer shell of this sensor, and a copper-made ring structure is selected, with holes opened on both sides of each electrode; according to the different work completed by the electrodes and the differences in connection methods, they are divided into four parts, and the two electrodes in each part are connected to each other, specifically divided into two shielding electrodes, two outer measurement electrodes, two inner measurement electrodes, and one transmitting electrode, and the outer measurement electrode and the inner measurement electrode form a monitoring electrode.

[0009] The stainless steel probe tube tightly fixes the stainless steel outer shell of the sensor to the stainless steel probe rod through the threaded screw ports at both ends; during use, the entire structure of the sensor is wrapped by the surrounding rock formation, and annular grooves with the same depth but different widths are opened on the surface of the stainless steel probe tube to install the electrodes, and the positions of these grooves need to meet certain distribution parameters, and this parameter is calculated by the following formula:

[0010]

[0011] In the formula, γ is the groove position distribution parameter, D0 is the center distance between electrode 4 and the 1# shielding electrode 1; D1 and D2 are the center distances between electrode 4 and the 1# measuring outer electrode 2 and the 1# measuring inner electrode 3 respectively. The suitable value range for this sensor is 2.5 - 3. The copper electrodes are installed in the grooves on the outer side of the stainless steel probe housing of the sensor according to the designed distances. Through holes are opened on both sides of the electrodes, and they are fixed on the sensor housing with hollow pins. All surfaces except the outer surface are wrapped with insulating materials. The wires are connected to the main circuit board of the sensor through the hollow pins; on the premise that the positions of each electrode satisfy the distribution parameter, it is required that the widths of the two shielding electrodes are the same and between 6 - 8 cm, and the remaining electrodes can have the same width and between 2 - 3 cm.

[0012] The main circuit board of the sensor includes a CPU, a power supply module, a communication module, a voltage conditioning circuit, an ADC, a DAC, a phase detection module, and a voltage conversion circuit; among them, the ADC module and the DAC module are integrated inside the single-chip microcomputer. The output of the DAC is connected to the conditioning circuit through the analog output channel of the CPU. The output of the voltage conditioning circuit is connected to the shielding electrode. The transmitting electrode is connected to the phase detection module through a wire. The wire led out from the monitoring electrode is connected to the phase detection and voltage conversion circuit in two paths. One path is connected to the single-chip microcomputer through the I / O port after phase detection calculation, and the other path is connected to the analog acquisition channel of the CPU after being processed by the voltage conversion circuit; one end of the communication module is connected to the USART interface of the CPU, and the other end is connected to the energized copper cable and the stainless steel probe.

[0013] The CPU module is a minimum system centered on STM32F103RCT6, which is used to control the waveform shape and frequency of the output AC voltage signal, process the collected signals, and complete the communication function.

[0014] The power supply module converts the +12V DC voltage provided by the battery into DC ±12V, +5V, and +3.3V according to the power supply requirements of each chip on the main circuit board of the sensor to supply power to each chip on the main circuit board of the sensor.

[0015] The communication module is a serial communication circuit based on an RS485 communication chip, and its function is to convert the data of the CPU into a standard RS485 signal.

[0016] The voltage conditioning circuit consists of two parts: a DC bias circuit and an amplification circuit. Its device parameters are set in combination with the D / A output characteristics of this sensor and the requirements of the output signal. The 5532 chips of the bias circuit and the amplification circuit need to cooperate with resistors of specific resistance values to convert the sine wave signal output by the CPU into the ±5V sine signal required for measurement and transmit it to the transmitting electrode.

[0017] The ADC module and the DAC module are integrated by the CPU. The DAC module is connected to the voltage conditioning circuit and is used to convert the digital signal sent by the CPU into a sine wave signal. The ADC module is connected to the voltage conversion circuit and is used to convert the voltage signal collected by the monitoring electrode into a digital quantity.

[0018] One end of the phase detection circuit is connected to the ±5V sine signal sent by the voltage conditioning circuit, and the other end is connected to the signal measured by the electrode. The two signals are adjusted through the shaping circuit and the exclusive-OR gate circuit. The shaping circuit chip LM311 converts the sine signal into a square wave signal. After shaping, the two outputs are connected to the exclusive-OR gate circuit to compare the voltage measured by the monitoring electrode with the transmitted signal to obtain the phase difference between the two.

[0019] The voltage conversion circuit is connected outside the ADC conversion module and is used to preprocess the voltage collected by the monitoring electrode. The voltage conversion uses the chip LM7332 and cooperates with a resistor of a specific resistance value to convert the voltage amplitude into a voltage range of 0 to 3.3V that can be collected by the single-chip microcomputer.

[0020] The specific implementation process of the present invention is as follows: A borehole wall looseness sensor is installed at the rear end of the drill pipe of the kilometer drill rig. Through seven electrodes nested outside the stainless steel probe tube, the impedance of the borehole wall medium around the drill pipe is measured through the analog conditioning circuit, and the impedance value is matched with the phase difference measured by the phase detection circuit. The impedance value is converted into two standard analog quantity signals of resistance and reactance and transmitted to the CPU. The CPU matches the impedance value with its corresponding frequency, and obtains the state of the borehole wall medium according to the impedance parameter range of the medium at various frequencies in the corresponding database, and then judges the looseness degree of the medium at this time and evaluates the state of the current borehole wall. Before each measurement, set the standard range of the impedance of the coal seam medium in this area as a warning sign for the data. Upload the measurement data to the host computer system through the energized copper cable, display the measurement results and evaluation status on the host computer interface, and transmit the measurement results and evaluation status to the expert system for further exploration and utilization.

[0021] The method for evaluating the looseness of the borehole wall of the kilometer drill rig described in the present invention is a measurement standard summarized and verified by combining measurement theories: According to the characterization of the looseness degree of the medium at different frequencies, the looseness degree of the borehole wall medium during the actual measurement process is classified: the medium is stable l≤-5, good -5≤l≤-3, normal -3≤l≤-1, poor -1<l≤0, dangerous 0<l≤1, faulty l>1, a total of 6 types. Then, by judging the range where the looseness value l is located, the current looseness degree of the borehole wall can be obtained as stable, good, normal, poor, dangerous or faulty.

[0022] The beneficial effects of the present invention are as follows: An external electrode - internal main board structure combined with a probe rod is adopted. A dielectric looseness sensor is composed of a CPU, a power module, a communication module, a voltage conditioning circuit, an ADC, a DAC, a phase detection module, a voltage conversion circuit, and measurement electrodes. This sensor can measure the looseness degree of the medium on the borehole wall in a borehole with a diameter of about 10 cm, complete continuous measurement powered by a storage battery in a borehole several kilometers long, evaluate the current state of the drill rod and the borehole. The sensor circuit design meets the downhole safety standards, can communicate with the upper computer and immediately transmit the downhole situation back, thus improving the automation level of the detection of the in - hole state of the kilometer - level drill rig borehole. Description of the Drawings

[0023] Figure 1 is the sensor for measuring the looseness of the borehole wall of the mine gas drainage directional kilometer - level drill rig of the present invention;

[0024] Figure 2 is the circuit diagram of the sensor for measuring the looseness of the borehole wall of the directional kilometer - level drill rig of the present invention;

[0025] Figure 3 is the circuit diagram of the voltage conditioning module of the present invention;

[0026] Figure 4 is the circuit diagram of the phase detection module of the present invention;

[0027] Figure 5 is the circuit diagram of the voltage conversion circuit of the present invention;

[0028] Figure 6 is the power supply circuit of the present invention;

[0029] Figure 7 is the installation model diagram of the sensor of the present invention;

[0030] In the figure: 1, 1# shielding electrode; 2, 1# measuring external electrode; 3, 1# measuring internal electrode; 4, transmitting electrode; 5, 2# measuring internal electrode; 6, 2# measuring external electrode; 7, 2# shielding electrode; 8, insulating pad; 9, stainless - steel probe tube; 10, sensor housing; 11, battery; 12, sensor main circuit board; 13, power - supply copper cable; 14, input interface; 15, output interface. Detailed Embodiment

[0031] The following further describes the detailed embodiment of the present invention in conjunction with the drawings.

[0032] As Figure 1As shown in the figure, the sensor for measuring the looseness of the borehole wall of the mine-used directional kilometer drill for coalbed methane extraction provided by the present invention is a sensor designed to realize on-line monitoring of the state of the borehole wall of the mine-used directional kilometer drill for coalbed methane extraction on the basis of the existing technology. Its structure mainly includes: electrodes 1-7, stainless steel probe tube 9, sensor main circuit board 12, and battery 11. Electrodes 1-7 are respectively the 1# shield electrode 1, 1# measuring outer electrode 2, 1# measuring inner electrode 3, transmitting electrode 4, 2# measuring inner electrode 5, 2# measuring outer electrode 6, and 2# shield electrode 7. All the electrodes are nested in the grooves on the outer side of the stainless steel probe tube and are insulated and isolated through the same insulating pad 8. The measuring inner electrodes 3 and 4 and the measuring outer electrodes 5 and 6 are two pairs of monitoring electrodes of the sensor, and are hereinafter referred to as monitoring electrodes. The 1# shield electrode 1, 1# measuring outer electrode 2, 1# measuring inner electrode 3, transmitting electrode 4, 2# measuring inner electrode 5, 2# measuring outer electrode 6, and 2# shield electrode 7 are respectively connected to the sensor main circuit board 12 through wires. The sensor main circuit board 12 and the battery 11 are installed in the sensor housing 10 and are sealed with sealant. The positive pole of the power supply line of the sensor main circuit board 12 is connected to the power supply copper cable 13, and the negative pole is connected to the stainless steel probe tube 9. The two ends of the power supply copper cable 13 are respectively connected to the input interface 14 and the output interface 15; the output voltage of the lithium battery 11 is +12VDC.

[0033] In the above structure, the sensor main circuit board is composed of a CPU, a power module, a communication module, a voltage conditioning circuit, an ADC, a DAC, a phase detection module, and a voltage conversion circuit, as Figure 2 shown; among them, the ADC module and the DAC module are integrated inside the single-chip microcomputer. The output of the DAC is connected to the conditioning circuit through the analog output channel of the CPU. The output of the conditioning circuit is connected to the 1# shield electrode 1 and the 2# shield electrode 7. The transmitting electrode 4 is connected to the phase detection module through a wire. The wires led out from the monitoring electrodes are connected to the phase detection and voltage conversion circuits in two paths. One path is connected to the single-chip microcomputer through the I / O port after phase detection calculation, and the other path is connected to the CPU analog acquisition channel after being processed by the voltage conversion circuit.

[0034] The communication module is a serial communication circuit based on an RS485 communication chip. One end of it is connected to the USART interface of the CPU, and the other end is connected to the power-on copper cable and the stainless steel probe tube. The CPU sends out data packets, which are processed and converted into standard RS485 signals by the communication module and communicate with other devices through the power supply copper cable.

[0035] As Figure 3As shown, the voltage conditioning circuit consists of two parts: a DC bias circuit and an amplification circuit. When the DC bias circuit functions, it couples the analog quantity output by the CPU with the DC bias voltage. This circuit is composed of voltage-dividing resistors R1 and R2, operational amplifier Q1, proportional resistors R3 to R6, and resistor R7. The voltage-dividing resistors R1 and R2 are in series. One end of the series connection is connected to the +5V DC voltage, and the other end is grounded. The voltage drawn from the middle is connected to the proportional resistor R3. The other end of R3 is connected to the negative input terminal of the operational amplifier Q1 and is connected to the output terminal of Q1 through R4. The negative input terminal of Q1 is connected to the ground through R5. The positive input terminal of Q1 is divided into two paths. One path passes through resistor R6 and is connected to the DAC output channel V of the CPU i connection, and the other path passes through resistor R7 and is connected to the ground. The negative input terminal of the operational amplifier Q2 is connected to the output of the operational amplifier Q1 through resistor R8. The positive input terminal of Q2 is connected to the ground through resistor R9. A resistor R 10 is connected between the output terminal and the negative input terminal of Q2. The output V out of the entire voltage conditioning circuit is connected to the monitoring electrode and the phase detection circuit.

[0036] The function of the phase detection circuit is to calculate the phase difference between the voltage signal sent by the electrode and the acquired signal. As Figure 4 shown, this circuit consists of two parts: a shaping circuit and a calculation circuit. The shaping circuit includes switching diodes D1 to D4, resistors R 11 to R 14 , voltage comparators U1 and U2. The signal V in acquired by the monitoring electrode is connected to resistor R 11 , and then is connected to one end of the voltage comparator U1 in parallel with a pair of anti-parallel diodes D1 and D2. The output of the conditioning circuit is connected to R 12 , D3, D4, and the voltage comparator U2 in the same way. Finally, pull-up resistors R 13 and R 14 are respectively connected to the output terminals of the two voltage comparators. The calculation circuit is used to calculate the difference between the output values of the two voltage comparators. The two outputs of the shaping circuit are connected to the calculation chip U3. The output terminal of the chip is connected to the I / O interface of the CPU, and then the CPU completes the subsequent operation and processing work.

[0037] Figure 5 The circuit is a voltage conversion circuit, and its function is to convert the voltage acquired on the monitoring electrode into a range that can be processed by the ADC module. This circuit is composed of the operational amplifier Q3 and three resistors R 15 , R 16 , R 17 . The input voltage is divided by the voltage-dividing resistors R 15 , R 16 and then connected to the input terminal of the operational amplifier Q3. The signal output terminal of the circuit is connected to the ADC module through resistor R 17Connect to the ADC analog input channel of the CPU.

[0038] The power supply voltages of the CPU and each part of the circuit are different. The power supply circuit structure is as Figure 6 shown. This circuit consists of two parts: a +12VDC to +5VDC circuit and a +12VDC to ±12VDC circuit. The +12VDC to +5VDC circuit consists of capacitors C1 to C7, resistors R 18 to R 22 , inductor L1, and DC conversion chip U4. The +12VDC DC input voltage at the power supply terminal is connected to one end of the capacitors C1, C2, and C3 connected in parallel, and the other ends of the three capacitors are grounded. The +12VDC DC input voltage is also connected to pin 8 of the DC conversion chip U4. Pin 3 of the DC conversion chip U4 is connected to the voltage input terminal through a protection resistor R 18 , pin 4 is connected to the ground, pin 7 is grounded through a resistor R 19 and the grounding terminal, pin 2 is connected to pin 1 through a capacitor C4, pin 1 is connected to the inductor L1, pin 5 is connected to the midpoint lead of the voltage dividing resistors R 20 and R 21 , and pin 6 is grounded through an RC series circuit composed of a capacitor C5 and a resistor R 22 . The inductor L1 outputs +5VDC voltage. Capacitors C6 and C7 are connected in parallel, one end is connected to the +5VDC output, and the other end is grounded. The +12VDC to ±12V circuit consists of a boost chip U5, resistors R 23 and R 24 , voltage transformer L2, diodes D5 and D6, and capacitors C8 to C 14 . The +12VDC input voltage is connected to pin 2 of the boost chip U5, and at the same time, it is connected to a pair of parallel capacitors C8 and C9, and the end of the parallel capacitors is grounded; pin 3 of U5 is connected to the midpoint of the voltage dividing resistors R 23 and R 24 , pins 7 and 8 of U5 are both grounded, and pins 5 and 6 are connected and then the output is connected to the same-name and different-name ends of the A end of the voltage transformer L2. The same-name end of the A winding of the voltage transformer L2 is connected to the +12VDC input voltage, the same-name end of the B winding is grounded, and the different-name end is connected to the different-name end of the C winding through a capacitor C 10 and then connected to the positive pole of the diode D5. The same-name end of the C winding is the +12Vout output, outputting +12VDC voltage, and this output terminal is connected to the ground through a capacitor C 11 . One end of the capacitor C 12 is connected to pin 5 of the boost chip U5, and the other end is connected to the different-name end of the B winding of the voltage transformer L2, and then connected to the positive pole of the diode D6. The output -12Vout of the diode D2 is the -12VDC voltage output, and this output terminal is connected to a pair of parallel capacitors C 13 and C14 , the other end of the shunt capacitor bank is grounded.

[0039] As shown in the appendix Figure 7 , the stainless-steel housing of the sensor is tightly fixed to the stainless-steel probe through the threaded screw ports at both ends. The entire structure is surrounded by rock strata. The copper measurement electrodes 1-7 are distributed on the outside of the sensor at the designed distances. There are holes on both sides of each electrode, and it is fixed to the sensor housing with hollow pins. All surfaces except the outer surface are wrapped with insulating materials. The wires are connected to the main board through the hollow pins. In addition, after introducing the wires, all the pins are sealed with glue, strictly sealed to the outside world. The measurement circuit main board is placed at the center of the sensor. There is hydraulic liquid passing through the probe. The power supply and the main board are integrated in the slender cylindrical control cavity, fixed by rubber brackets around. The communication copper cable passes through the cavity, and the electrode wires enter from one end, and then the two ends of the control cavity are sealed with glue to isolate from the liquid environment in the probe. The working mode in the control cavity is as Figure 2 shown. The power supply module converts the DC 12V voltage provided by the battery and supplies power to the CPU and each sub-module chip. A sine signal (the frequency can be adjusted in integer multiples of 1kHz) generated by the CPU is converted into a ±5V sine signal through the voltage conditioning circuit. This sine signal flows to the transmitting electrode 4 and the 1# shielding electrode 1 and the 2# shielding electrode 7 at the same time; the transmitted ±5V sine signal flows through the surrounding medium and then returns to the monitoring electrode (formed by the combination of the 1# measurement outer electrode 2, the 1# measurement inner electrode 3, the 2# measurement inner electrode 5, and the 2# measurement outer electrode 6). The voltage measured by the monitoring electrode will be transmitted back to the phase detection circuit and the voltage conversion circuit for calculation. The phase detection circuit processes the voltage measured by the monitoring electrode and the transmitted signal to obtain the phase difference between the two. The voltage conversion circuit raises the voltage measured by the monitoring electrode and then transmits it to the ADC module of the CPU for conversion, and calculates the voltage drop U of the impedance of the borehole wall medium M , and then brings the current value I0 of the transmitting electrode and this voltage drop U M into the calculation formula to obtain the looseness of the medium around the sensor during measurement

[0040] According to the data measured by the sensor, bring each parameter into the following calculation formula:

[0041]

[0042] In the formula, λ is the impedance of the coal seam medium, and its value represents the impedance information of the medium of the current measured borehole wall. D0 is the center distance between the electrode 4 and the 1# shielding electrode 1. D1 and D2 are the center distances between the electrode 4 and the 1# measurement outer electrode 2 and the 1# measurement inner electrode 3 respectively. Then, according to the measured phase difference θ, it is separated to obtain the resistance ρ R and ρ XTwo parts, and then further refine the analysis according to the change characteristics of the two parameters at different frequencies, and define the looseness value l. The calculation formula of the medium looseness is as follows:

[0043]

[0044] In the formula, ρ R and ρ X are the real part and the imaginary part of the impedance value separated by the phase difference respectively; k is the frequency coefficient. The set frequencies of this sensor are all integer multiples of 1 kHz, and the multiple is the k value.

[0045] According to the numerical range divided by the looseness l from low to high, the hole wall state can be divided into 6 categories: medium stable l ≤ -5, good -5 ≤ l ≤ -3, normal -3 ≤ l ≤ -1, poor -1 < l ≤ 0, dangerous 0 < l ≤ 1, failure l > 1, a total of 6 types. By comparing the medium looseness at different frequencies respectively, more detailed results in the frequency domain can be obtained.

[0046] With the change of the type and property of the medium around the sensor, the numerical values of the coal and rock looseness at different frequency bands will change significantly. Due to the existence of drilling fluid flow inside the borehole, when there are fractures or collapses in the surrounding rock layer of the sensor, the addition of drilling fluid will significantly enhance the electrical conductivity of the coal seam, and its looseness value will decrease rapidly, reaching the alarm threshold, and sending an alarm message to the upper computer. Generally, during the normal drilling process, there will be no drilling fluid staying near the sensor for a long time. Therefore, the looseness value of the coal seam will not be lower than the warning threshold, and it can collect data of the surrounding medium. Using the looseness value, the state of the borehole coal and rock can be divided into the above six categories.

Claims

1. A sensor for measuring the looseness of the borehole wall of a directional kilometer drill for coalbed methane extraction in mines, characterized in that: The measurement sensor mainly consists of an electrode, a stainless steel probe tube, a main circuit board of the sensor, and a battery. The stainless steel probe tube tightly fixes the stainless steel shell of the sensor to the stainless steel probe rod through the threaded screw ports at both ends. During use, the entire structure of the sensor is wrapped by the surrounding rock formation. Ring-shaped grooves with the same depth but different widths are opened on the surface of the stainless steel probe tube to install the electrodes. The electrode is a copper ring-shaped structure with holes on both sides. The copper electrodes are installed in the grooves on the outer side of the stainless steel probe tube of the sensor at the designed distances. By opening holes on both sides of the electrode, it is fixed to the sensor shell with a hollow plug. All surfaces except the outer surface are wrapped with insulating materials. The wire is connected to the main circuit board of the sensor through the hollow plug. According to the different work completed by the electrodes and the differences in connection methods, it is divided into four parts, and the two electrodes in each part are connected to each other. Specifically, it is divided into two shielding electrodes, two external measurement electrodes, two internal measurement electrodes, and one transmitting electrode. Among them, the external measurement electrode and the internal measurement electrode form a monitoring electrode. The main circuit board of the sensor includes a CPU, a power module, a communication module, a voltage conditioning circuit, an ADC, a DAC, a phase detection module, and a voltage conversion circuit. Among them, the ADC module and the DAC module are integrated inside the single-chip microcomputer. The output of the DAC is connected to the conditioning circuit through the analog output channel of the CPU. The output of the voltage conditioning circuit is connected to the shielding electrode. The transmitting electrode is connected to the phase detection module through a wire. The wires led out from the monitoring electrode are connected to the phase detection module and the voltage conversion circuit in two ways. One way is connected to the single-chip microcomputer through the I / O port after being calculated by the phase detection module, and the other way is connected to the analog acquisition channel of the CPU after being processed by the voltage conversion circuit. One end of the communication module is connected to the USART interface of the CPU, and the other end is connected to the energized copper cable and the stainless steel probe tube. The power module converts the +12V DC voltage provided by the battery into DC ±12V, +5V, and +3.3V according to the power supply requirements of each chip on the main circuit board of the sensor to supply power to each chip on the main circuit board of the sensor. The ring-shaped grooves on the surface of the stainless steel probe tube need to meet certain distribution parameters, which are calculated by the following formula: ； In the formula, γ is the distribution parameter of the groove position, D0 is the center distance between the electrode (4) and the 1# shielding electrode (1); D1 and D2 are the center distances between the electrode (4) and the 1# external measurement electrode (2), 1# internal measurement electrode (3) respectively. The suitable value range for this sensor is 2.5 - 3. The CPU module is a minimum system centered on STM32F103RCT6, which is used to control the waveform shape and frequency of the output AC voltage signal, process the collected signals, and complete communication.

2. The borehole wall looseness measurement sensor for the mine coalbed methane drainage directional kilometer drill according to claim 1, characterized in that: On the premise that the position of the electrode meets the distribution parameters, it is required that the widths of the two shielding electrodes are the same and between 6 - 8 cm, and the widths of the remaining electrodes are the same and between 2 - 3 cm.

3. The borehole wall looseness measurement sensor for the mine coalbed methane drainage directional kilometer drill according to claim 1, characterized in that: The communication module is a serial communication circuit based on an RS485 communication chip, and its function is to convert the data of the CPU into a standard RS485 signal.

4. The measurement sensor for the looseness of the borehole wall of the directional kilometer drill for coalbed methane drainage in mines according to claim 1, characterized in that: The voltage conditioning circuit consists of two parts: a DC bias circuit and an amplification circuit. Its device parameters are set in combination with the D / A output characteristics of this sensor and the requirements of the output signal. The 5532 chips of the bias circuit and the amplification circuit need to cooperate with resistors of specific resistance values to convert the sine wave signal output by the CPU into a ±5V sine signal required for measurement and transmit it to the emitting electrode.

5. The borehole wall looseness measurement sensor for the mine coalbed methane drainage directional kilometer drill according to claim 1, characterized in that: One end of the phase detection module is connected to the ±5V sine signal sent by the voltage conditioning circuit, and the other end is connected to the signal measured by the electrode. The two signals are adjusted through a shaping circuit and an exclusive-OR gate circuit. The shaping circuit chip LM311 converts the sine signal into a square wave signal. After shaping, the two outputs are connected to the exclusive-OR gate circuit to compare the voltage measured by the monitoring electrode with the transmitted signal to obtain the phase difference between the two.

6. The borehole wall looseness measurement sensor for the mine coalbed methane drainage directional kilometer drill according to claim 1, characterized in that: The voltage conversion circuit is connected outside the ADC conversion module and is used to preprocess the voltage collected by the monitoring electrode. The voltage conversion uses the chip LM7332, which cooperates with resistors of specific resistance values to convert the voltage amplitude into a voltage range of 0 to 3.3V that can be collected by the single-chip microcomputer.

7. The borehole wall looseness measurement sensor for the mine coalbed methane drainage directional kilometer drill according to claim 1, characterized in that: According to the characterization of the looseness of the medium at different frequencies, the looseness of the hole wall medium during the actual measurement process is classified as follows: stable medium l ≤ -5, good -5 ≤ l ≤ -3, normal -3 ≤ l ≤ -1, poor -1 < l ≤ 0, dangerous 0 < l ≤ 1, faulty l > 1, a total of 6 types.

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