CN118549468A - System and method for identifying coal and rock characters in drilling process based on electromagnetic detection - Google Patents

Abstract

A system and method for identifying coal rock properties during drilling based on electromagnetic detection, the system: two strip grooves are provided on the drill rod, which is assembled on the drilling platform, and its head end is connected to the output shaft of the hydraulic motor in the drilling platform; microstrip antennas one and two are respectively installed at the ends of the two strip grooves; the electric rotary joint is sleeved on the outside of the head end of the drill rod; two coaxial cables are respectively embedded in the two strip grooves, and ports one and two of the vector network analyzer are respectively connected to microstrip antennas one and two through two coaxial cables. Method: The loss parameters of different coal rock properties under laboratory conditions are obtained; under actual working conditions, the reflected electromagnetic waves of different coal rock properties are collected, and the return loss and insertion loss are calculated, and the type of current coal rock is determined in combination with the loss parameters obtained in the laboratory. The system and method can accurately identify the coal rock properties in real time during the drilling operation, and can provide reliable technical support for realizing intelligent drilling pressure relief operations.

Description

A system and method for identifying coal and rock properties during drilling based on electromagnetic detection

Technical Field

The present invention belongs to the technical field of intelligent identification, and in particular relates to a system and method for identifying coal and rock properties during drilling based on electromagnetic detection.

Background Art

In recent years, with the increase in the depth of coal mining, the number of mines experiencing rock burst disasters has increased significantly, posing a great threat to mine safety production, and drilling pressure relief is an important technical means to prevent and control rock burst. At present, pressure relief operations still use manually operated drilling rigs for drilling construction, which often encounters problems such as low drilling efficiency, shallow drilling depth, and frequent accidents in the hole. In addition, it is difficult to effectively identify the coal and rock properties during the drilling process, making it impossible to adjust the working parameters such as rotation speed and thrust pressure in time, which will lead to an increase in drilling construction time and even damage to the drill bit. In the process of automated drilling construction, the recognition effect of coal and rock properties while drilling determines the control performance of underground drilling operations, and is a prerequisite for improving drilling pressure relief efficiency and ensuring intelligent drilling operations.

Since the coal and rock properties of underground pressure relief tunnels are complex and changeable, and the structure of drilling equipment is relatively complex and the sensor signal noise is high, as the drilling depth increases, the collected vibration signals, drilling torque, pressure and other sensor signals cannot fully characterize the current coal and rock drilling status, resulting in the above-mentioned traditional identification methods being unable to meet the actual identification needs. Electromagnetic waves have the characteristics of strong penetration, stable propagation, and high sensitivity, so electromagnetic detection technology has been widely used in geological exploration, medical imaging and other fields. In addition, due to the different electromagnetic parameters of different coal and rock properties, the absorption loss and reflection degree of different coal and rock to electromagnetic signals are also very different. Therefore, the accurate identification of coal and rock properties while drilling can be achieved through the difference characteristics of electromagnetic signals of different coal and rock. However, in the existing technology, there is a lack of technical means for effectively applying electromagnetic detection technology to the identification of coal and rock properties during the process of drilling pressure relief. For this reason, it is urgent to provide a technical means based on electromagnetic detection to solve the problem of coal and rock property identification during drilling pressure relief, so as to provide reliable technical support for the realization of intelligent drilling pressure relief operations.

Summary of the invention

In view of the problems existing in the above-mentioned prior art, the present invention provides a system and method for identifying coal and rock properties during drilling based on electromagnetic detection. The system has low manufacturing cost and reliable real-time communication performance. It can accurately identify the coal and rock properties in real time during the drilling operation, which is conducive to timely adjustment of working parameters such as rotation speed and thrust pressure during the drilling pressure relief process, and can provide reliable technical support for realizing intelligent drilling pressure relief operations. The method has simple implementation steps, high intelligence and good real-time performance. It can accurately identify the surrounding coal and rock properties online during the drilling process, which can effectively solve the problem of coal and rock property identification during the drilling pressure relief process, and is suitable for large-scale promotion and application.

In order to achieve the above-mentioned object, the present invention provides a system for identifying coal and rock properties during drilling based on electromagnetic detection, comprising a drilling platform, a drill rod, a first microstrip antenna, a second microstrip antenna, an electric rotary joint, a coaxial cable and a vector network analyzer;

The drill rod has two strip grooves arranged in parallel along the length direction, the first ends of the two strip grooves start at a position close to the first end of the drill rod and end at a position close to the last end of the drill rod; the drill rod is mounted on the drilling platform, and the first end of the drill rod is connected to the output shaft of the hydraulic motor in the drilling platform;

The center frequencies of the microstrip antenna 1 and the microstrip antenna 2 are both 5.6 GHz, and they are respectively installed at the ends of the two strip-shaped slots, and are used to convert the received outgoing electrical signals into outgoing electromagnetic waves, and transmit the outgoing electromagnetic waves to the outside world, and at the same time, are used to receive reflected electromagnetic waves and convert the reflected electromagnetic waves into return electrical signals;

The rotor end of the electric rotary joint is fixedly sleeved on the outside of the head end of the drill pipe, and the stator end of the electric rotary joint is fixedly connected to the drilling platform;

Two coaxial cables are respectively embedded in the two strip grooves, and the ends of the two coaxial cables are respectively connected to the microstrip antenna 1 and the microstrip antenna 2, and the head ends of the two coaxial cables are respectively connected to the two wiring terminals on the rotor end of the electric rotary joint;

Port 1 and port 2 of the vector network analyzer are respectively connected to two terminals on the stator end of the electric rotary joint, and are used to transmit an outgoing electrical signal 1 and an electrical signal 2 to microstrip antenna 1 and microstrip antenna 2 respectively through port 1 and port 2 and two coaxial cables, and at the same time, are used to receive a return electrical signal emitted by microstrip antenna 1 and microstrip antenna 2 respectively through port 1 and port 2 and two coaxial cables.

As a preferred embodiment, the microstrip antenna 1 and the microstrip antenna 2 are of the same model, with a radiation patch width of 16.9 mm and a length of 13.3 mm, a substrate width of 35 mm and a length of 30 mm, a dielectric plate thickness of 1 mm and a dielectric constant of 3.3.

Furthermore, in order to ensure that the identification results can be obtained more efficiently and accurately, the model of the vector network analyzer is E5071C, and its frequency test range is 0.6GHz to 8.5GHz.

In the present invention, two strip grooves are provided on the rod body of the drill rod, so that two coaxial cables can be fixedly embedded in the two strip grooves respectively. In this way, during the drilling operation, the coal rock can be prevented from damaging the coaxial cable, and the reliable transmission of the monitoring signal during the real-time drilling process is ensured. Microstrip antenna one and microstrip antenna two are respectively installed at the ends of the two strip grooves, and they are connected to the ends of the two coaxial cables. After the electrical signal is transmitted through the coaxial cable at the analysis device end, it can be converted into an electromagnetic wave signal through the microstrip antenna, and then emitted into the outside air. At the same time, after the microstrip antenna receives the reflected electromagnetic wave signal from the coal rock, it can be converted into a return electrical signal and transmitted to the analysis device end through the coaxial cable. Since the difference between different coal rock properties in the frequency band range of 5.6GHz is more obvious, therefore, the microstrip antenna with a center frequency of 5.6GHz is selected to transmit the outgoing electromagnetic wave and receive the reflected electromagnetic wave, which can be conducive to quickly and accurately obtaining the identification result, and helps to reduce the amount of calculation, reduce the demand for the computing power of the analysis equipment, and indirectly reduce the identification cost. An electric rotary joint is set at the head end of the drill pipe, and the two terminals on the rotor end are connected to two coaxial cables. At the same time, the two terminals on the stator end are connected to port 1 and port 2 of the vector network analyzer respectively. This ensures that the vector network analyzer and the microstrip antenna can communicate reliably in real time during the rotation of the drill pipe, ensuring that the microwave signal can be reliably transmitted to the microstrip antenna, and at the same time, ensuring that the reflected wave received by the microstrip antenna can be timely and reliably transmitted back to the vector network analyzer. Since the reception and transmission of microwave signals are calculated in nanoseconds, and the rotation speed of the drill pipe is generally around 150r/min, the relative movement between the drill pipe and the coal rock can be ignored during each transmission and reception of the electromagnetic signal of the coal rock while drilling. In addition, the identification of coal and rock properties during the drilling process mainly relies on the electromagnetic reflection waves of coal and rock. The drill pipe, as a lossy medium, has a great hindering effect on the propagation of electromagnetic waves. Therefore, two microstrip antennas are symmetrically installed on the surface of the drill pipe and then connected to the vector network analyzer through a coaxial cable. This can obtain all the information on the surrounding coal and rock properties under real-time drilling conditions to the maximum extent, and can effectively avoid the weakening of electromagnetic waves by lossy media during propagation, which is conducive to obtaining more accurate identification results.

The system has low manufacturing cost and reliable real-time communication performance. It can accurately identify coal and rock properties in real time during drilling operations, which is conducive to timely adjustment of working parameters such as rotation speed and thrust pressure during drilling pressure relief, and can provide reliable technical support for the realization of intelligent drilling pressure relief operations.

The present invention also provides a method for identifying coal rock properties during drilling based on electromagnetic detection, using a coal state identification system during drilling based on electromagnetic detection, characterized in that it includes the following methods:

Step 1: Obtain loss parameters under laboratory conditions;

The return loss S11 and insertion loss S21 of different coal rock properties at 5.6GHz were determined under laboratory conditions;

Step 2: Obtain the loss parameters under actual working conditions and determine the type of current coal rock;

S21: Control the hydraulic motor on the drilling platform to start working, and use the hydraulic motor to drive the drill rod to perform drilling operations;

S22: Control the vector network analyzer to start working, so that port 1 and port 2 of the vector network analyzer transmit outgoing electrical signal 1 and outgoing electrical signal 2 to microstrip antenna 1 and microstrip antenna 2 respectively through two coaxial cables, and use microstrip antenna 1 and microstrip antenna 2 to convert the received outgoing electrical signal 1 and outgoing electrical signal 2 into outgoing electromagnetic wave 1 and outgoing electromagnetic wave 2, and transmit them to the outside;

The center frequencies of the microstrip antenna 1 and the microstrip antenna 2 are both 5.6 GHz;

S23: using electromagnetic waves 1 and 2 reflected from the coal rock surface and propagating in the air to form reflected electromagnetic waves 1 and 2, and at the same time, receiving reflected electromagnetic waves 1 and 2 through microstrip antenna 1, and converting reflected electromagnetic waves 1 and 2 into rotational electric signals 1A and 2A, and then transmitting them to port 1 of a vector network analyzer through coaxial electromagnetic transmission, receiving reflected electromagnetic waves 1 and 2 through microstrip antenna 2, and converting reflected electromagnetic waves 1 and 2 into rotational electric signals 1B and 2B, and then transmitting them to port 1 of a vector network analyzer through coaxial electromagnetic transmission;

S24: Analyze and process the signal using a vector network analyzer to obtain loss parameters under actual working conditions; obtain return loss S11 by the ratio of the energy of the rotating electrical signal A to the energy of the emitted electrical signal, obtain insertion loss S12 by the ratio of the energy of the rotating electrical signal A to the energy of the emitted electrical signal, obtain return loss S22 by the ratio of the energy of the rotating electrical signal B to the energy of the emitted electrical signal, and obtain insertion loss S21 by the ratio of the energy of the rotating electrical signal B to the energy of the emitted electrical signal;

S25: Compare the return loss S11 and insertion loss S21 under actual working conditions with the return loss S11 and insertion loss S21 under laboratory conditions to determine the type of current coal rock.

As a preferred embodiment, in step 1, the calculation process of the return loss S11 and the insertion loss S21 is as follows:

S01: Establish a two-port network measurement model for microwave properties of solid materials;

The medium to be measured has two end surfaces, namely plane one and plane two. Electromagnetic waves are incident from the air at a certain angle to point A of plane one of the medium to be measured. A part of the electromagnetic waves is reflected at point A, and another part of the electromagnetic waves enters the medium to be measured from point A and propagates forward to point B of plane two. A part of the electromagnetic waves at point B continues to propagate forward through plane two, and another part of the electromagnetic waves at point B is reflected and reaches point C of plane one. A part of the electromagnetic waves at point C continues to propagate back through plane one, and another part of the electromagnetic waves at point C is reflected to point D of plane two, and a part of the electromagnetic waves at point D continues to propagate forward through plane two.

S02: According to the definition of scattering parameters, formula (1) and formula (2) are obtained respectively;

V _r =S ₁₁ V _i (1);

V _T =S ₂₁ V _i (2);

Where, S11 is the return loss parameter; S21 is the insertion loss parameter; Vi _is the incident voltage when the electromagnetic signal emitted by the microstrip antenna reaches the surface of the medium to be measured after propagation; _Vr is the total reflected voltage; _VT is the total transmitted voltage;

S03: Obtain the expressions of the total reflected voltage V _r and the total transmitted voltage V _T by using formula (3) and formula (4) respectively;

In the formula, Γ represents the reflection coefficient of the electromagnetic wave at one point on the plane of the medium to be measured, and T represents the transmission coefficient of the electromagnetic wave on the medium to be measured;

S04: Let V _i = 1, and obtain formula (5) and formula (6) respectively according to the two-port network measurement model;

S05: According to the equivalent two-port theory, formula (7) and formula (8) are obtained;

T = e ^-γd (8);

Where _ηr is the normalized characteristic impedance of the medium to be measured, in Ω, and γ is the propagation constant of the electromagnetic wave in the medium to be measured;

S06: transform formula (7) and formula (8) to obtain formula (9) and formula (10) respectively;

Where, d is the thickness of the medium to be measured;

S07: The relationship between _ηr and γ and electromagnetic parameters is obtained by formula (11) and formula (12) respectively;

In the formula, ε _p is the complex dielectric constant, μ _p is the complex magnetic permeability, and for non-magnetic materials such as coal and rock, μ _p takes the value of 1;

S08: Combining the above formulas, the calculation formula (13) of the relative complex dielectric constant ε _p of the medium to be measured is obtained;

Wherein, γ ₀ represents the propagation constant of electromagnetic wave in free space, γ ₀ =j2π/λ ₀ ;

S09: Formula (14) is obtained by formula (13);

ε _p =ε′-jε″ (14);

Where ε′ is the first-order derivative of ε _p , and ε″ is the second-order derivative of ε _p ;

S10: The electromagnetic field loss of the medium to be tested is calculated by formula (15);

In the formula, ε _r is the relative dielectric constant of the medium to be measured, ε _r =ε/ε ₀ , where ε is the real part of the dielectric constant of the medium, ε ₀ is the dielectric constant in vacuum, which is 8.85×10 ^-12 F/m; ω is the angular frequency of the electromagnetic wave;

S11: Substitute formula (15) into formula (14) to calculate ε _p , and continue to reverse to obtain η _r and γ as well as Γ and T, and further substitute them into formula (5) and formula (6) to obtain S11 and S21.

In the present invention, the return loss S11 and insertion loss S21 of different coal rock properties at 5.6GHz are first determined by using the reflected wave signal intensity under laboratory conditions, which can provide reliable technical support for comparative analysis in the subsequent identification process. During the drilling operation, the microwave signal emitted by the vector network analyzer is sent to the microstrip antenna at the end of the drill rod through the coaxial cable embedded in the drill rod strip groove, and then converted into electromagnetic waves by the microstrip antenna and emitted to the surrounding air. At the same time, the electromagnetic waves reflected by the coal rock are received by the microstrip antenna, and converted into return electrical signals and transmitted to the vector network analyzer through the coaxial cable. This can avoid the situation where the drill rod is directly used as the electromagnetic wave transmission medium and the energy and amplitude of the electromagnetic wave are weakened, which is conducive to obtaining all information about the surrounding coal rock properties in real time during drilling, and thus can help to obtain more accurate identification results. After obtaining the return loss and insertion loss of different coal rocks under actual working conditions, the recognition results can be quickly obtained by comparing them with the return loss and insertion loss obtained in the laboratory.

The method has simple implementation steps, a high degree of intelligence, and good real-time performance. It can accurately identify the surrounding coal and rock properties online during the drilling process, and can effectively solve the problem of coal and rock property identification during borehole pressure relief, and is suitable for large-scale promotion and application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of the system of the present invention;

FIG2 is a schematic diagram of the structure of a microstrip antenna 1 or a microstrip antenna 2 in the present invention;

FIG3 is a schematic diagram of the structure of the electric rotary joint in the present invention;

FIG4 is a schematic diagram of the assembly of the drill rod and the microstrip antenna in the present invention;

FIG5 is a schematic diagram of a two-port network measurement model in the present invention;

FIG6 is a loss curve diagram of lignite at different frequencies in the present invention;

FIG7 is a graph showing the loss of bituminous coal at different frequencies in the present invention;

FIG8 is a loss curve diagram of anthracite at different frequencies in the present invention;

FIG9 is a loss curve diagram of shale at different frequencies in the present invention;

FIG10 is a loss curve diagram of mudstone at different frequencies in the present invention;

FIG11 is a graph showing the loss of sandstone at different frequencies in the present invention;

FIG12 is a graph showing return loss curves of six coal rock properties at different frequencies in the present invention;

FIG13 is a graph showing insertion loss of six coal rock properties at different frequencies in the present invention;

FIG. 14 is a schematic diagram of the extreme values of six coal rock properties at different frequencies in the present invention.

In the figure: 1. Vector network analyzer; 2. Coaxial cable; 3. Electric rotary joint; 4. Drill rod; 5. Drilling platform; 6. Microstrip antenna 1; 7. Microstrip antenna 2; 8. Strip slot.

DETAILED DESCRIPTION

The present invention will be further described below.

As shown in Figures 1 to 4, the present invention provides a system for identifying coal and rock properties during drilling based on electromagnetic detection, including a drilling platform 5, a drill rod 4, a microstrip antenna 1 6, a microstrip antenna 2 7, an electric rotary joint 3, a coaxial cable 2 and a vector network analyzer 1;

The drilling platform 5 is powered by a hydraulic motor and performs drilling and propulsion by controlling a hydraulic cylinder;

The drill rod 4 has two strip grooves 8 arranged in parallel along the length direction, the head ends of the two strip grooves 8 start at a position close to the head end of the drill rod 4 and end at a position close to the tail end of the drill rod 4; the drill rod 4 is assembled on the drilling platform 5, and the head end thereof is connected to the output shaft of the hydraulic motor in the drilling platform 5;

The center frequencies of the microstrip antenna 1 6 and the microstrip antenna 2 7 are both 5.6 GHz, and they are respectively installed at the ends of the two strip-shaped slots 8, and are used to convert the received outgoing electrical signals into outgoing electromagnetic waves, and transmit the outgoing electromagnetic waves to the outside, and at the same time, are used to receive reflected electromagnetic waves and convert the reflected electromagnetic waves into return electrical signals;

The electric rotary joint 3 is mainly composed of a stator end, a rotor end, a wire, a screw and a stop plate. Signals can be transmitted during rotation and can withstand a high-intensity rotation speed of 20,000 rpm. The inner diameter of the rotor end is 50 mm, which cooperates with the drill rod 5 and is fixed with screws; the outer diameter of the stator end is 119 mm, which is fixed by connecting the stop plate to the fixing block. The rotor end of the electric rotary joint 3 is fixedly sleeved on the outside of the head end of the drill rod 4, and the stator end of the electric rotary joint 3 is fixedly connected to the drilling platform 5;

Two coaxial cables 2 are respectively embedded in two strip grooves 8, and the ends of the two coaxial cables 2 are respectively connected to the microstrip antenna 1 6 and the microstrip antenna 2 7, and the head ends of the two coaxial cables 2 are respectively connected to the two wiring terminals on the rotor end of the electric rotary joint 3;

The vector network analyzer 1 (VNA) is a multi-channel microwave receiver that can transmit and receive electromagnetic waves through multiple ports, and process the amplitude and phase of the received electromagnetic wave signals. It can accurately measure the energy of electromagnetic waves. In order to ensure that the identification results can be obtained more efficiently and accurately, the classic model E5071C vector network analyzer is used, and its frequency test range is 0.6GHz~8.5GHz. It can perform dual-port S parameter measurement with a very high measurement accuracy. Scattering parameters such as return loss S11 and insertion loss S21 can be measured, where S11 represents the scattering parameter emitted by port 1 and measured by port 1, which is the ratio between the energy received by port 1 and the energy emitted by port 1 as the transmitting end, and represents the return loss, that is, how much energy is reflected back to the transmitting source end; S21 represents the scattering parameter emitted by port 1 and measured by port 2, which is the ratio between the energy received by port 2 and the energy emitted by port 1, and represents the insertion loss, that is, how much energy is transmitted from port 1 to port 2. The vector network analyzer mainly consists of four parts: excitation signal source, signal separation device, receiver, and processing and display unit.

Port one and port two of the vector network analyzer 1 are respectively connected to two terminals on the stator end of the electric rotary joint 3, and are used to transmit the transmitted electrical signal one and the electrical signal two to the microstrip antenna one 6 and the microstrip antenna two 7 through port one and port two and two coaxial cables 2, and at the same time, are used to receive the return electrical signals emitted by the microstrip antenna one 6 and the microstrip antenna two 7 through port one and port two and two coaxial cables 2.

In the present invention, two strip grooves are provided on the rod body of the drill rod, so that two coaxial cables can be fixedly embedded in the two strip grooves respectively. In this way, during the drilling operation, the coal rock can be prevented from damaging the coaxial cable, and the reliable transmission of the monitoring signal during the real-time drilling process is ensured. Microstrip antenna one and microstrip antenna two are respectively installed at the ends of the two strip grooves, and they are connected to the ends of the two coaxial cables. After the electrical signal is transmitted through the coaxial cable at the analysis device end, it can be converted into an electromagnetic wave signal through the microstrip antenna, and then emitted into the outside air. At the same time, after the microstrip antenna receives the reflected electromagnetic wave signal from the coal rock, it can be converted into a return electrical signal and transmitted to the analysis device end through the coaxial cable. Since the difference between different coal rock properties in the frequency band range of 5.6GHz is more obvious, therefore, the microstrip antenna with a center frequency of 5.6GHz is selected to transmit the outgoing electromagnetic wave and receive the reflected electromagnetic wave, which can be conducive to quickly and accurately obtaining the identification result, and helps to reduce the amount of calculation, reduce the demand for the computing power of the analysis equipment, and indirectly reduce the identification cost. An electric rotary joint is set at the head end of the drill pipe, and the two terminals on the rotor end are connected to two coaxial cables. At the same time, the two terminals on the stator end are connected to port 1 and port 2 of the vector network analyzer respectively. This ensures that the vector network analyzer and the microstrip antenna can communicate reliably in real time during the rotation of the drill pipe, ensuring that the microwave signal can be reliably transmitted to the microstrip antenna, and at the same time, ensuring that the reflected wave received by the microstrip antenna can be timely and reliably transmitted back to the vector network analyzer. Since the reception and transmission of microwave signals are calculated in nanoseconds, and the rotation speed of the drill pipe is generally around 150r/min, the relative movement between the drill pipe and the coal rock can be ignored during each transmission and reception of the electromagnetic signal of the coal rock while drilling. In addition, the identification of coal and rock properties during the drilling process mainly relies on the electromagnetic reflection waves of coal and rock. The drill pipe, as a lossy medium, has a great hindering effect on the propagation of electromagnetic waves. Therefore, two microstrip antennas are symmetrically installed on the surface of the drill pipe and then connected to the vector network analyzer through a coaxial cable. This can obtain all the information on the surrounding coal and rock properties under real-time drilling conditions to the maximum extent, and can effectively avoid the weakening of electromagnetic waves by lossy media during propagation, which is conducive to obtaining more accurate identification results.

The system has low manufacturing cost and reliable real-time communication performance. It can accurately identify coal and rock properties in real time during drilling operations, which is conducive to timely adjustment of working parameters such as rotation speed and thrust pressure during drilling pressure relief, and can provide reliable technical support for the realization of intelligent drilling pressure relief operations.

As a preferred embodiment, the microstrip antenna 1 6 and the microstrip antenna 2 7 are of the same model, with a radiation patch width of 16.9 mm and a length of 13.3 mm, a substrate width of 35 mm and a length of 30 mm, a dielectric plate thickness of 1 mm and a dielectric constant of 3.3.

When the hydraulic motor in the drilling platform 5 rotates, it drives the drill rod 4 to move for drilling operations. At this time, the vector network analyzer 1 transmits an electrical signal through feeding. The electrical signal is transmitted to the microstrip antenna 1 6 and the microstrip antenna 2 7 through the coaxial cable 2 and the electrical rotary joint 3, and emits electromagnetic waves. The electromagnetic waves are propagated from the air to the surface of the coal rock mass and reflected. At this time, the two microstrip antennas receive the reflected wave signal and transmit it back to the vector network analyzer 1 along the original route to complete the storage, processing and analysis of the received signal.

The characteristic parameters that determine the propagation of electromagnetic waves in coal rock media include: relative dielectric constant ε _r , conductivity σ and magnetic permeability μ. The relative dielectric constant determines the propagation speed of electromagnetic waves in the medium, the conductivity affects the penetration depth of electromagnetic waves, and the magnetic permeability, for non-magnetized media such as coal rock, can be considered to be the same as the magnetic permeability in vacuum, and the value is 1.

In order to explore the influence of electromagnetic parameters of different types of coal rock on the propagation characteristics of electromagnetic waves, the electromagnetic parameter values of the following different types of coal rock media are determined, as shown in Table 1.

Table 1 Electromagnetic parameters of different medium

The principle of coal and rock identification through electromagnetic waves is that electromagnetic waves will be reflected when they propagate from one medium to another, so the intensity of the received reflected wave signal can be used for detection.

As shown in Figures 6 to 11, these are the S parameters of six coal rock properties, where S11 and S22 are the signal strength ratios of antenna 1 and antenna 2, respectively; S21 is the signal strength ratio of antenna 1 to antenna 2; and S12 is the signal strength ratio of antenna 2 to antenna 1. For the six coal rock properties, lignite, bituminous coal, anthracite, shale, mudstone, and sandstone, S11 = S22 and S21 = S12, but there are differences in the reflected wave signal strength among the six.

Since S11=S22 and S21=S12 for the six types of coal rock properties, namely lignite, bituminous coal, anthracite, shale, mudstone and sandstone, the antenna reflected wave signal is simplified into an analysis of S11 and S21 parameters.

Figure 12 shows the changes of the S11 parameter curves of the six coal rock properties at different frequencies. In general, the reflected wave signal intensity decreases first and then increases with the increase of frequency. The difference is more obvious at the microstrip antenna operating frequency of 5.6 GHz, and the reflected wave signal intensity has a minimum value near this frequency. The frequencies corresponding to the minimum reflected waves of lignite, bituminous coal, anthracite, shale, mudstone and sandstone are 5.432 GHz, 5.436 GHz, 5.532 GHz, 5.552 GHz, 5.516 GHz and 5.468 GHz respectively.

It can be seen from Figure 13 that the S21 parameter curves of the six coal rock properties generally show that with the increase of frequency, the reflected wave signal intensity first gradually increases, then suddenly decreases, and finally slowly increases. However, at 4-5GHz and 6-8GHz, due to the enhanced scattering, the result change pattern is not obvious. The reflected wave signal intensity received by antenna 1 from antenna 2 fluctuates greatly. In the range of 5-6GHz, the reflected wave signal intensity is basically stable, showing a trend of first increasing and then decreasing. The maximum value also appears near the operating frequency of the microstrip antenna, 5.6GHz.

S (σ, ε _r ) is defined as different coal rock properties and their main electromagnetic parameters, electrical conductivity and relative dielectric constant. S is the type of coal rock, such as lignite, bituminous coal, anthracite, shale, mudstone and sandstone; σ and ε _r are the electrical conductivity and relative dielectric constant of the coal rock property, respectively. The extreme values of S parameters of six coal rock properties are plotted as shown in Figure 14.

Comparing the extreme values of reflected wave signals of six coal rock properties, namely lignite, bituminous coal, anthracite, shale, mudstone and sandstone, the S11 extreme value does not change much with the increase of frequency, and the S21 extreme value fluctuates with the increase of frequency, but the difference in signal intensity between lignite and bituminous coal, anthracite, shale and sandstone is still not obvious. The extreme values of S11 parameters of lignite, bituminous coal, anthracite, shale, mudstone and sandstone are -8.014dB, -7.542dB, -7.614dB, -7.439dB, -7.475dB and -7.488dB respectively; the extreme values of S21 parameters are -34.581dB, -33.317dB, -38.624dB, -29.562dB, -21.348dB and -36.124dB respectively.

To this end, the present invention also provides a method for identifying coal rock properties during drilling based on electromagnetic detection, using a coal state identification system during drilling based on electromagnetic detection, characterized in that it includes the following methods:

Step 1: Obtain loss parameters under laboratory conditions;

The return loss S11 and insertion loss S21 of different coal rock properties at 5.6GHz were determined under laboratory conditions;

Step 2: Obtain the loss parameters under actual working conditions and determine the type of current coal rock;

S21: Control the hydraulic motor on the drilling platform 5 to start working, and use the hydraulic motor to drive the drill rod 4 to perform drilling operations;

S22: Control the vector network analyzer 1 to start working, so that the port 1 and the port 2 of the vector network analyzer 1 transmit the outgoing electrical signal 1 and the outgoing electrical signal 2 to the microstrip antenna 1 6 and the microstrip antenna 2 7 respectively through the two coaxial cables 2, and use the microstrip antenna 1 6 and the microstrip antenna 2 7 to convert the received outgoing electrical signal 1 and the outgoing electrical signal 2 into the outgoing electromagnetic wave 1 and the outgoing electromagnetic wave 2, and transmit them to the outside;

Wherein, the center frequencies of the microstrip antenna 1 6 and the microstrip antenna 2 7 are both 5.6 GHz;

S23: using the electromagnetic wave 1 and the electromagnetic wave 2 reflected from the surface of the coal rock mass and propagating in the air to form the reflected electromagnetic wave 1 and the reflected electromagnetic wave 2, at the same time, receiving the reflected electromagnetic wave 1 and the reflected electromagnetic wave 2 through the microstrip antenna 1 6, and converting the reflected electromagnetic wave 1 and the reflected electromagnetic wave 2 into a rotational electric signal 1A and a rotational electric signal 2A, and then transmitting them to the port 1 of the vector network analyzer 1 through the coaxial electromagnetic transmission, receiving the reflected electromagnetic wave 1 and the reflected electromagnetic wave 2 through the microstrip antenna 2 7, and converting the reflected electromagnetic wave 1 and the reflected electromagnetic wave 2 into a rotational electric signal 1B and a rotational electric signal 2B, and then transmitting them to the port 1 of the vector network analyzer 1 through the coaxial electromagnetic transmission;

S24: Analyze and process the signal using a vector network analyzer 1 to obtain loss parameters under actual working conditions; obtain return loss S11 by the ratio of the energy of the rotating electrical signal A to the energy of the emitted electrical signal, obtain insertion loss S12 by the ratio of the energy of the rotating electrical signal A to the energy of the emitted electrical signal, obtain return loss S22 by the ratio of the energy of the rotating electrical signal B to the energy of the emitted electrical signal, and obtain insertion loss S21 by the ratio of the energy of the rotating electrical signal B to the energy of the emitted electrical signal;

S25: Compare the return loss S11 and insertion loss S21 under actual working conditions with the return loss S11 and insertion loss S21 under laboratory conditions to determine the type of current coal rock.

As a preferred embodiment, in step 1, the calculation process of the return loss S11 and the insertion loss S21 is as follows:

S01: Establish a two-port network measurement model for microwave properties of solid materials;

FIG5 shows a schematic diagram of electromagnetic wave propagation in a uniform dielectric material. When the incident wave enters the surface of the dielectric material from the air, reflection and refraction will occur, and then continue to propagate in the dielectric material to the other surface to continue to reflect and refract, until the electromagnetic wave in the dielectric material is completely lost. Specifically, the medium to be measured has two end surfaces, namely plane one and plane two. The electromagnetic wave is incident from the air to point A of plane one of the medium to be measured at a certain angle. A part of the electromagnetic wave is reflected at point A, and another part of the electromagnetic wave enters the medium to be measured from point A and propagates forward to point B of plane two. A part of the electromagnetic wave at point B continues to propagate forward through plane two, and another part of the electromagnetic wave at point B is reflected and reaches point C of plane one. A part of the electromagnetic wave at point C continues to propagate back through plane one, and another part of the electromagnetic wave at point C is reflected to point D of plane two. A part of the electromagnetic wave at point D continues to propagate forward through plane two.

In FIG5 , Γ represents the reflection coefficient of the electromagnetic wave at one plane of the dielectric material. According to the symmetry, the reflection coefficient at the second plane is -Γ, T represents the transmission coefficient of the electromagnetic wave on the dielectric material, and d is the thickness of the dielectric material.

S02: According to the definition of scattering parameters, formula (1) and formula (2) are obtained respectively;

V _r =S ₁₁ V _i (1);

V _T =S ₂₁ V _i (2);

Where, S11 is the return loss parameter; S21 is the insertion loss parameter; Vi _is the incident voltage when the electromagnetic signal emitted by the microstrip antenna reaches the surface of the medium to be measured after propagation; _Vr is the total reflected voltage; _VT is the total transmitted voltage;

S03: Obtain the expressions of the total reflected voltage V _r and the total transmitted voltage V _T by using formula (3) and formula (4) respectively;

S04: Let V _i = 1, and obtain formula (5) and formula (6) respectively according to the two-port network measurement model;

S05: According to the equivalent two-port theory, formula (7) and formula (8) are obtained;

T = e ^-γd (8);

Where _ηr is the normalized characteristic impedance of the medium to be measured, in Ω, and γ is the propagation constant of the electromagnetic wave in the medium to be measured;

S06: transform formula (7) and formula (8) to obtain formula (9) and formula (10) respectively;

S07: The relationship between _ηr and γ and electromagnetic parameters is obtained by formula (11) and formula (12) respectively;

In the formula, ε _p is the complex dielectric constant, μ _p is the complex magnetic permeability, for non-magnetic materials of coal and rock, μ _p ≈1, where μ _p is taken as 1;

S08: Combining the above formulas, the calculation formula (13) of the relative complex dielectric constant ε _p of the medium to be measured is obtained;

Wherein, γ ₀ represents the propagation constant of electromagnetic wave in free space, γ ₀ =j2π/λ ₀ ;

S09: Formula (14) is obtained by formula (13);

ε _p =ε′-jε″ (14);

Where ε′ is the first-order derivative of ε _p , and ε″ is the second-order derivative of ε _p ;

S10: In order to reflect the consumption of the electromagnetic field by the conductivity, the electromagnetic field loss of the medium to be measured is calculated by formula (15);

In the formula, ε _r is the relative dielectric constant of the medium to be measured. Since the dielectric constant of the medium is the product of the relative dielectric constant of the medium and the dielectric constant in vacuum, ε _r =ε/ε ₀ , where ε is the real part of the dielectric constant of the medium, ε ₀ is the dielectric constant in vacuum, which is 8.85×10 ^-12 F/m; ω is the angular frequency of the electromagnetic wave;

S11: Substitute formula (15) into formula (14) to calculate ε _p , and continue to reverse to obtain η _r and γ as well as Γ and T, and further substitute them into formula (5) and formula (6) to obtain S11 and S21.

In the present invention, the return loss S11 and insertion loss S21 of different coal rock properties at 5.6GHz are first determined by using the reflected wave signal intensity under laboratory conditions, which can provide reliable technical support for comparative analysis in the subsequent identification process. During the drilling operation, the microwave signal emitted by the vector network analyzer is sent to the microstrip antenna at the end of the drill rod through the coaxial cable embedded in the drill rod strip groove, and then converted into electromagnetic waves by the microstrip antenna and emitted to the surrounding air. At the same time, the electromagnetic waves reflected by the coal rock are received by the microstrip antenna, and converted into return electrical signals and transmitted to the vector network analyzer through the coaxial cable. This can avoid the situation where the drill rod is directly used as the electromagnetic wave transmission medium and the energy and amplitude of the electromagnetic wave are weakened, which is conducive to obtaining all information about the surrounding coal rock properties in real time during drilling, and thus can help to obtain more accurate identification results. After obtaining the return loss and insertion loss of different coal rocks under actual working conditions, the recognition results can be quickly obtained by comparing them with the return loss and insertion loss obtained in the laboratory.

The method has simple implementation steps, a high degree of intelligence, and good real-time performance. It can accurately identify the surrounding coal and rock properties online during the drilling process, and can effectively solve the problem of coal and rock property identification during borehole pressure relief, and is suitable for large-scale promotion and application.

Claims (5)

1. The coal and rock character recognition system in the drilling process based on electromagnetic detection comprises a drilling platform (5) and a drill rod (4), and is characterized by further comprising a microstrip antenna I (6), a microstrip antenna II (7), an electric rotary joint (3), a coaxial cable (2) and a vector network analyzer (1);

Two strip-shaped grooves (8) are formed in the rod body of the drill rod (4) in parallel along the length direction, and the head ends of the two strip-shaped grooves (8) start at a position close to the head end of the drill rod (4) and stop at a position close to the tail end of the drill rod (4); the drill rod (4) is assembled on the drilling platform (5), and the head end of the drill rod is connected with an output shaft of a hydraulic motor in the drilling platform (5);

The center frequency of the first microstrip antenna (6) and the center frequency of the second microstrip antenna (7) are both 5.6GHz and are respectively arranged at the tail ends of the two strip-shaped grooves (8) and used for converting received emergent electric signals into emergent electromagnetic waves and transmitting the emergent electromagnetic waves to the outside, and meanwhile, the first microstrip antenna and the second microstrip antenna are used for receiving reflected electromagnetic waves and converting the reflected electromagnetic waves into return electric signals;

the rotor end of the electric rotary joint (3) is fixedly sleeved outside the head end of the drill rod (4), and the stator end of the electric rotary joint (3) is fixedly connected with the drilling platform (5);

The two coaxial cables (2) are respectively embedded in the two strip-shaped grooves (8), the tail ends of the two coaxial cables (2) are respectively connected with the microstrip antenna I (6) and the microstrip antenna II (7), and the head ends of the two coaxial cables (2) are respectively connected with two wiring ends on the rotor end of the electric rotary joint (3);

the first port and the second port of the vector network analyzer (1) are respectively connected with two wiring ends on the stator end of the electric rotary joint (3) and are used for respectively transmitting outgoing electric signals I and II to the microstrip antenna I (6) and the microstrip antenna II (7) through the first port and the second port and two coaxial cables (2), and simultaneously, are used for respectively receiving return electric signals transmitted by the microstrip antenna I (6) and the microstrip antenna II (7) through the first port and the second port and the two coaxial cables (2).

2. The system for identifying coal and rock characteristics in a drilling process based on electromagnetic detection according to claim 1, wherein the microstrip antenna I (6) and the microstrip antenna II (7) are the same in model, the radiating patch is 16.9mm in width and 13.3mm in length, the substrate is 35mm in width and 30mm in length, the dielectric plate is 1mm in thickness, and the dielectric constant is 3.3.

3. The system for identifying coal and rock characteristics in a drilling process based on electromagnetic detection according to claim 1 or 2, wherein the model of the vector network analyzer (1) is E5071C, and the frequency test range is 0.6 GHz-8.5 GHz.

4. An electromagnetic detection-based coal and rock character recognition method in a drilling process, which adopts the electromagnetic detection-based coal and coal character recognition system in the drilling process according to any one of claims 1 to 3, is characterized by comprising the following steps,

Step one: obtaining loss parameters under laboratory conditions; determining the return loss S11 and the insertion loss S21 of different coal rock characteristics at 5.6GHz under laboratory conditions, wherein the specific process is as follows;

Step two: obtaining loss parameters under actual working conditions, and determining the type of the current coal rock;

s21: controlling a hydraulic motor on a drilling platform (5) to start working, and driving a drill rod (4) to perform drilling operation by using the hydraulic motor;

S22: the vector network analyzer (1) is controlled to start to work, so that a first port and a second port of the vector network analyzer (1) respectively transmit an outgoing electric signal I and an outgoing electric signal II to a first microstrip antenna (6) and a second microstrip antenna (7) through two coaxial cables (2), and the first microstrip antenna (6) and the second microstrip antenna (7) are utilized to convert the received outgoing electric signal I and the received outgoing electric signal II into an outgoing electromagnetic wave I and an outgoing electromagnetic wave II and transmit the outgoing electromagnetic wave I and the outgoing electromagnetic wave II to the outside;

the center frequencies of the first microstrip antenna (6) and the second microstrip antenna (7) are 5.6GHz;

S23: the method comprises the steps of utilizing the surface of a coal rock body to reflect electromagnetic waves I and II which propagate in air to form reflected electromagnetic waves I and II, receiving the reflected electromagnetic waves I and II through a microstrip antenna I (6), converting the reflected electromagnetic waves I and II into a rotary electric signal A and a rotary electric signal II A, transmitting the rotary electric signal A and the rotary electric signal II A to a port I of a vector network analyzer (1) through coaxial electromagnetic waves, receiving the reflected electromagnetic waves I and II through a microstrip antenna II (7), converting the reflected electromagnetic waves I and II into a rotary electric signal B and a rotary electric signal II, and transmitting the rotary electric signal B and the rotary electric signal B to the port I of the vector network analyzer (1) through coaxial electromagnetic waves;

S24: analyzing and processing the signals by using a vector network analyzer (1) to obtain loss parameters under actual working conditions; the method comprises the steps of obtaining return loss S11 through the ratio of energy of a first rotary electric signal A to energy of a first emergent electric signal, obtaining insertion loss S12 through the ratio of energy of a second rotary electric signal A to energy of the first emergent electric signal, obtaining return loss S22 through the ratio of energy of a second rotary electric signal B to energy of the second emergent electric signal, and obtaining insertion loss S21 through the ratio of energy of the first rotary electric signal B to energy of the first emergent electric signal;

S25: and comparing the return loss S11 and the insertion loss S21 under the actual working condition with the return loss S11 and the insertion loss S21 under the laboratory condition, and determining the type of the current coal rock.

5. The method for identifying coal and rock characteristics in a drilling process based on electromagnetic detection according to claim 4, wherein in the first step, the calculation process of the return loss S11 and the insertion loss S21 is as follows:

s01: establishing a two-port network measurement model of the microwave characteristics of the solid material;

The medium to be measured is provided with two end surfaces, namely a first plane and a second plane, the electromagnetic wave is incident to a point A of the first plane of the medium to be measured at a certain angle in the air, one part of the electromagnetic wave is reflected at the point A, the other part of the electromagnetic wave enters the medium to be measured from the point A and forwards propagates to a point B of the second plane, one part of the electromagnetic wave at the point B continuously propagates forwards through the second plane, the other part of the electromagnetic wave at the point B is reflected and reaches a point C of the first plane, one part of the electromagnetic wave at the point C continuously returns through the first plane, the other part of the electromagnetic wave at the point C is reflected to a point D of the second plane, and one part of the electromagnetic wave at the point D continuously propagates forwards through the second plane;

s02: respectively obtaining a formula (1) and a formula (2) according to the definition of the scattering parameter;

V_r＝S₁₁V_i (1)；

V_T＝S₂₁V_i (2)；

Wherein S11 is a return loss parameter; s21 is an insertion loss parameter; v _i is the incident voltage when the electromagnetic signal emitted by the microstrip antenna reaches the surface of the medium to be measured through propagation; v _r is the total reflected voltage; v _T is the total transmission voltage;

S03: the expressions of the total reflected voltage V _r and the total transmitted voltage V _T are obtained by the formula (3) and the formula (4), respectively;

wherein Γ represents the reflection coefficient of the electromagnetic wave at one position of the plane of the medium to be measured, and T represents the transmission coefficient of the electromagnetic wave on the medium to be measured;

S04: let V _i =1, according to the two-port network measurement model, get equation (5) and equation (6) respectively;

s05: obtaining a formula (7) and a formula (8) according to an equivalent two-port theory;

Wherein eta _r is the normalized characteristic impedance of the medium to be measured, the unit is omega, and gamma is the propagation constant of electromagnetic waves in the medium to be measured;

S06: deforming the formula (7) and the formula (8) to obtain a formula (9) and a formula (10) respectively;

Wherein d is the thickness of the medium to be measured;

S07: respectively obtaining the relation between eta _r and gamma and electromagnetic parameters through a formula (11) and a formula (12);

Wherein epsilon _p is complex dielectric constant, mu _p is complex magnetic permeability, and mu _p is 1 for a coal rock non-magnetized substance;

S08: combining the above formulas to obtain a calculation formula (13) of the relative complex dielectric constant epsilon _p of the medium to be measured;

Wherein, gamma ₀ represents the propagation constant of electromagnetic waves in free space, gamma ₀＝j2π/λ₀;

S09: obtaining a formula (14) through a formula (13);

ε_p＝ε′-jε″ (14)；

Where ε 'is the first derivative of ε _p and ε' is the second derivative of ε _p;

S10: the loss of the electromagnetic field by the medium to be measured is calculated by the formula (15);

Wherein epsilon _r is the relative dielectric constant of the medium to be measured, epsilon _r＝ε/ε₀ is the real part of the dielectric constant of the medium, epsilon ₀ is the dielectric constant in vacuum, and the value is 8.85 multiplied by 10 ^-12 F/m; omega is the angular frequency of the electromagnetic wave;

s11: and substituting the formula (15) into the formula (14) to obtain epsilon _p, continuing back-pushing to obtain eta _r, gamma and T, and further substituting the formula (5) and the formula (6) to obtain S11 and S21.