Mining small-diameter while-drilling electromagnetic wave resistivity measuring instrument

Abstract

The utility model discloses a mining small-diameter while-drilling electromagnetic wave resistivity measuring instrument which comprises a non-magnetic drill collar, and a transmitter unit, a transmitting antenna, two receiver units, two receiving antennas, a signal processing, storage and communication unit and a power management unit are arranged on the non-magnetic drill collar. According to the measuring instrument disclosed by the utility model, on the premise that on-site use conditions are met, through calculation of a theoretical chart, optimization of an instrument antenna array design, an electrical function design, an electrical intrinsic safety design and a ground software design, and simplification of a mechanical structure design, the instrument is enabled to meet use requirements under a mine, on-site construction efficiency is improved, and cost is saved.

Description

Technical Field

[0001] This utility model relates to the field of coal mine exploration, specifically to an intrinsically safe small-diameter electromagnetic resistivity measuring instrument for drilling. Background Technology

[0002] In recent years, in the field of logging while drilling (LWD) for oil and gas exploration, with the improvement of measurement accuracy and reliability and the increase in measurement information, LWD technology has received increasing attention. LWD and related technologies have developed rapidly, and their application scope is constantly expanding, especially in drilling engineering and reservoir evaluation. By the end of the 20th century, major international oil companies had successfully commercialized their LWD electromagnetic resistivity logging instruments after several generations of product development. Currently, product technology continues to develop to higher levels, such as azimuth resistivity measurement and anisotropic formation measurement with tilted antennas, which can meet the needs of accurate measurement and detailed interpretation of complex formations. Research on LWD technology in China started relatively late, and only a few companies have successfully launched and commercialized LWD electromagnetic resistivity logging instruments.

[0003] Currently, logging-while-drilling (LWD) electromagnetic resistivity logging tools are mainly used in oil and gas exploration, with a minimum outer diameter of 4.75". However, in coal mining exploration, with the advancement of intelligent coal mining, real-time access to the geological and stratigraphic information of the borehole is crucial. Due to constraints such as high coal seam resistivity, small borehole diameter, complex site conditions, intrinsic safety certification requirements, and high costs, LWD electromagnetic resistivity logging tools used in oil and gas exploration cannot yet be directly applied to coal mining.

[0004] Chinese invention patent CN105019891A belongs to the field of electromagnetic resistivity logging technology in coal mine drilling, specifically relating to an electromagnetic resistivity logging instrument and its measurement method in coal mine drilling. It utilizes the propagation effect of electromagnetic waves in a medium to measure the relative changes of two characteristic parameters (phase difference and amplitude ratio) of two electromagnetic fields to obtain the resistivity of the formation, which can be used to delineate formations and detect geological anomalies. This invention can meet most drilling measurements in coal mines. The drill collar has an outer diameter of 73mm, and the measuring section is a sealed structure placed inside the drill collar via a bracket. A circuit board is placed inside the section, which can withstand a water pressure of 12MPa. The instrument uses a dual-transmitter, dual-receiver antenna configuration, operating at two specific frequencies between 0.3MHz and 4MHz. One cycle consists of alternating transmissions. When one transmitting antenna is working, the two receiving antennas simultaneously receive electromagnetic wave signals from the formation. The signals are conditioned through two signal processing channels, and the amplitude ratio and phase difference are measured. After one cycle, the measurement results are uploaded to the wellhead monitor. After inversion, four sets of phase difference and amplitude ratio resistivity data are obtained, completing one measurement operation.

[0005] The main drawback of this patent is that it uses a dual-transmitter, dual-receiver antenna array, which results in a long instrument length, causing significant difficulties for on-site construction and machining. The cost of instrument materials and machining is also high, and the instrument consumes a lot of power. If battery power is used, the working time in a single well is short. In addition, the instrument circuit board is installed inside the drill collar, which makes the instrument assembly, debugging and maintenance inconvenient. Utility Model Content

[0006] To address the technical problems of existing instruments being too long, having a large outer diameter, poor high-resistivity response, high cost, and failing to meet intrinsic safety requirements, this invention provides a small-diameter electromagnetic resistivity measuring instrument that can be used in the field of coal mining.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] An improved small-diameter electromagnetic resistivity measuring instrument for mining drilling is characterized by the following features: it includes a non-magnetic drill collar, and a transmitter unit, a transmitting antenna, two receiver units, two receiving antennas, a signal processing, storage and communication unit, and a power management unit are installed on the non-magnetic drill collar.

[0009] The transmitter unit includes a microprocessor, a DDS circuit module, an elliptic filter module, a programmable gain amplifier module, an RF power amplifier module, and a dual-frequency matching network module, which are electrically connected together in sequence. The dual-frequency matching network module is electrically connected to the transmitting antenna.

[0010] The two receiver units have the same structure, each including a front-end dual-frequency matching network, a low-noise amplifier, a mixer module, and an intermediate frequency amplification and filtering module that are electrically connected together in sequence. The front-end dual-frequency matching network is electrically connected to a receiving antenna, and the intermediate frequency amplification and filtering module is electrically connected to the dual-channel high-speed AD acquisition module in the signal processing, storage and communication unit described below.

[0011] The signal processing, storage and communication unit includes a DSP module and a dual-channel high-speed AD acquisition module electrically connected to the DSP module, a large-capacity data storage module, and a communication module;

[0012] The power management unit supplies power to the various components within the aforementioned measuring instrument.

[0013] Furthermore, a ring antenna compartment for placing the antenna coil and a square circuit board compartment for placing the circuit board are opened on the outer wall of the non-magnetic drill collar. n wiring holes are machined inside the skeleton of the non-magnetic drill collar, and the middle of the non-magnetic drill collar is a mud flow channel.

[0014] Furthermore, a non-metallic frame of a certain thickness is installed inside the antenna housing, and a certain number of rectangular slots are opened along the circumference of the non-metallic frame. The magnetic strips are embedded in the rectangular slots, and then a certain number of coils are wound on the non-metallic frame. Finally, the antenna cover is covered and sealed with epoxy glue.

[0015] Furthermore, the antenna compartment and the circuit board compartment are electrically connected via a sealed plug; a read / write inspection port is also provided on the outer wall of the non-magnetic drill collar.

[0016] Furthermore, the signal processing, storage, and communication unit also includes a clock management module and a PIC microprocessor module.

[0017] Furthermore, the power management unit includes a DC-DC power module, an EMI filter module, a switching circuit, and a microcontroller.

[0018] Furthermore, the measuring instrument has an outer diameter of 89mm, a source distance of 30”≤L≤46”, operates at two specific frequencies between 0.4MHz and 5MHz, has a total length of no more than 2m, and the distance between the two receiving antennas is 8”≤d≤14”.

[0019] The beneficial effects of this utility model are:

[0020] The measuring instrument disclosed in this utility model, under the premise of meeting the on-site use conditions, optimizes the design of the instrument antenna array, electrical function design, intrinsically safe electrical design and ground software design through calculation of theoretical drawings, simplifies the mechanical structure design, so that the instrument meets the needs of underground use, improves on-site construction efficiency and saves costs;

[0021] The measuring instrument disclosed in this utility model is an intrinsically safe instrument, and compared with other drilling electromagnetic resistivity measuring instruments, it has the advantages of being shorter, lighter, having lower power consumption, lower cost, and stronger high-resistivity response capability.

[0022] The measuring instrument disclosed in this utility model achieves a high degree of integration of electrical functions and low power consumption by using low-power devices, optimized power management design and magnetic loading process. It can extend the working time in the hole when powered by battery, and save construction costs while reducing the number of drilling trips.

[0023] The measuring instrument disclosed in this utility model adopts a single-transmitter, dual-receiver structure through antenna array design combined with theoretical drawings. This reduces power consumption by reducing transmission, shortens the instrument length, and overcomes the problem of limited space in underground mining operations.

[0024] The measuring instrument disclosed in this utility model makes full use of the space between the antennas on the drill collar wall and places the circuit board in a slot on the drill collar wall, which shortens the length of the instrument, making it easier to install and improves the convenience of debugging and maintenance. Attached Figure Description

[0025] Figure 1 This is a block diagram of the measuring instrument disclosed in Embodiment 1 of this utility model;

[0026] Figure 2a This is a schematic diagram of the non-magnetic drill collar of the measuring instrument disclosed in Embodiment 1 of this utility model in the 0° direction;

[0027] Figure 2b This is a schematic diagram of the non-magnetic drill collar of the measuring instrument disclosed in Embodiment 1 of this utility model in the 120° direction;

[0028] Figure 2c This is a schematic diagram of the non-magnetic drill collar of the measuring instrument disclosed in Embodiment 1 of this utility model in the 240° direction;

[0029] Figure 3 It is a graph showing the conversion between phase difference and resistivity;

[0030] Figure 4 It is a graph showing the conversion between amplitude ratio and resistivity. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0032] Example 1 discloses a small-diameter electromagnetic resistivity measuring instrument for mining, an intrinsically safe product designed specifically for underground drilling. During underground drilling (exploratory drilling) operations, it is installed between the drill bit and drill rod to measure the phase difference and amplitude ratio between two receiving antennas in real time during drilling. The measured values ​​are transmitted to a host computer (holehead computer) in real time. Combined with the hole depth and the instrument's theoretical chart, the instrument calculates and displays the current changes in formation resistivity, thus reflecting the lithological changes in the formation. This provides data reference for real-time adjustment of the drill bit's drilling direction to ensure the drill bit penetrates the target layer. This instrument has the advantages of short length, small outer diameter, good high-resistivity measurement performance, low cost, and convenient field use.

[0033] like Figure 1 As shown, it includes a non-magnetic drill collar, and on the non-magnetic drill collar are arranged a transmitter unit 2, a transmitting antenna, two receiver units 3, two receiving antennas, a signal processing, storage and communication unit 4, and a power management unit 5; it adopts a one-transmit dual-receive antenna array, with a total of three antennas and two specific operating frequencies.

[0034] like Figure 2a , 2bAs shown in Figure 2c, a ring antenna compartment 12 for placing the antenna coil and a square circuit board compartment 11 for placing the circuit board are opened on the outer wall of the non-magnetic drill collar. In order to realize the electrical connection between the circuit boards, n wiring holes are processed in the skeleton of the non-magnetic drill collar. The middle of the non-magnetic drill collar is a mud flow channel.

[0035] A non-metallic frame of a certain thickness is installed inside the antenna housing, and a certain number of rectangular slots are made along the circumference of the non-metallic frame. Five to twenty magnetic strips are axially embedded into the rectangular slots. Then, 1 to 15 turns of coil are wound on the non-metallic frame. Finally, a semi-circular radome is placed on top and sealed with epoxy resin (potting). The radome can receive and transmit electromagnetic waves and prevent the antenna coil from being worn during drilling. The epoxy resin potting can protect the coil from mud and water erosion.

[0036] The antenna compartment and the circuit board compartment are electrically connected by a sealing plug compartment 13 to ensure a good seal; a read / write inspection port 14 is also provided on the outer wall of the non-magnetic drill collar.

[0037] The transmitter unit includes a microprocessor, a DDS circuit module, an elliptic filter module, a programmable gain amplifier module, an RF power amplifier module, and a dual-frequency matching network module, which are electrically connected together in sequence. The dual-frequency matching network module is electrically connected to the transmitting antenna to realize high-frequency signal transmission with "power agility" and "frequency agility".

[0038] The microprocessor controls the DDS circuit module to generate a stepped sine wave or square wave signal of a specific frequency. After passing through a high-order (e.g., 9th order) elliptic filter module, a pure sine wave signal is obtained. Then, after being amplified by a programmable gain amplifier module, the signal amplitude is controllable and variable. The RF power amplifier module amplifies the signal and inputs it to the dual-frequency matching network module for feeding to the transmitting antenna.

[0039] The two receiver units have identical structures, each including a front-end dual-frequency matching network, a low-noise amplifier, a mixer module, and an intermediate frequency amplification and filtering module electrically connected together in sequence. The front-end dual-frequency matching network is electrically connected to one receiving antenna, and the intermediate frequency amplification and filtering module is electrically connected to the dual-channel high-speed AD acquisition module in the signal processing, storage, and communication unit described below. The weak signal received by the receiving antenna is amplified by the low-noise amplifier through the front-end dual-frequency matching network to obtain a high-frequency signal that meets certain amplitude requirements. After frequency conversion by the mixer module, a mixed signal with rich frequencies is obtained. A low-pass filter with a cutoff frequency of 8KHz is designed to filter out high-frequency and other frequency signals, resulting in a pure intermediate frequency sine wave signal. The intermediate frequency signal frequency can be designed to be 1KHz to 6KHz, and then amplified to a certain amplitude.

[0040] The signal processing, storage, and communication unit includes a DSP module and a dual-channel high-speed AD acquisition module electrically connected to the DSP module, a large-capacity data storage module, and a communication module. The unit also includes a clock management module and a PIC microprocessor module. Two receiver units output two low-frequency sine wave signals. These signals are digitized by the dual-channel high-speed AD acquisition module (with a acquisition frequency of 8kHz to 32kHz). After processing using digital filtering and FFT algorithms, the phase difference and amplitude ratio of the two signals are obtained. The measurement data for each cycle is sent to the large-capacity data storage module for storage. Simultaneously, based on commands from the host computer, the current measurement data is transmitted in real-time to the host computer (ground software) via the communication module. After drilling is complete, the data stored in the instrument can be downloaded for more detailed analysis as needed.

[0041] Because there are many interference factors in the analog processing path of the received signal, in addition to the thermal noise generated by each device itself, high-frequency radiation and conducted interference of various frequencies are also introduced. However, due to the effect of filters and various EMI devices in the system, high-frequency interference is greatly suppressed. Therefore, the noise that finally enters the ADC system is mainly in-band thermal noise. The cumulative averaging method has a significant effect on the noise reduction of narrowband Gaussian white noise. By coherently accumulating the sampled original voltage signal V N times, the signal-to-noise ratio is improved by N times. Considering the real-time requirements of the system, N = 576 is taken in this algorithm, at which point the signal-to-noise ratio is improved by 27.6dB. Practice has proved that the cumulative averaging method is more effective and faster than the digital filtering method.

[0042] The ground software includes an instrument settings module, a testing module, a zero-lifting module, and a resistivity curve display module. The settings module handles functions such as instrument operating mode selection, sampling period setting, time synchronization, clock retrieval, and data download. The zero-lifting module displays and records aerial measurements during testing, which are needed for engineering value calculations during actual drilling. The testing module performs tests on the instrument during production and maintenance, displaying detailed measurement data, operating status, and error calculations, facilitating instrument production and troubleshooting. The resistivity curve display module uses an inversion algorithm to convert phase difference and amplitude ratio to resistivity, and displays resistivity curves at different hole depths, providing on-site personnel with intuitive data for adjusting drill bit direction. Figure 3 It is a graph showing the conversion between phase difference and resistivity; Figure 4 It is a graph showing the conversion between amplitude ratio and resistivity.

[0043] The resistivity curve display module of the ground software converts the phase difference and amplitude ratio data uploaded from the underground instruments to the borehole computer into phase difference and amplitude ratio resistivity data using a theoretical chart, enabling real-time monitoring of formation resistivity during drilling. The calculation method for the theoretical chart is described below:

[0044] In drilling electromagnetic wave propagation resistivity logging instruments, since the distance between the receiving antenna and the transmitting antenna is much larger than the radius of the transmitting antenna, the transmitting antenna can be approximated as a magnetic dipole. The following derives the formula for the electromagnetic field generated by the magnetic dipole and analyzes the relationship between the signal strength of the receiving antenna and the transmitting frequency, source distance, and formation electrical parameters.

[0045] Let the time-varying relationship of the emission source be exp(iωt), and define the direction of the magnetic moment as the z-axis. Then the Hertz potential F generated by a unit magnetic dipole in a homogeneous isotropic medium can be expressed as:

[0046]

[0047] Where F only has a component in the z direction, the electric field E can be calculated using the formula E=-iωμ▽×F:

[0048]

[0049] In the above formula, wavenumber Complex permittivity is defined as The unit imaginary component is given by ω, where ω is the angular frequency, μ is the permeability, σ is the conductivity, ε0 ​​is the permittivity in vacuum, and ε r The relative permittivity, (x′,y′,z′) are the coordinates of the transmitting source, and (x,y,z) are the coordinates of the receiving point.

[0050] After obtaining the expression for the electric field E at any point in space, the relationship between the magnetic field and the electric field... The H of the magnetic field can be easily obtained. x H y H z The expression for the component, if we also consider the receiving antenna as a magnetic dipole with its magnetic moment along the z-direction, is: V = -iωμH z For a single-transmitter, dual-receiver, three-coil system, let the amplitude and phase of the induced electromotive force of the near-receiving coil be |V1| and Φ1, respectively, and the amplitude and phase of the induced electromotive force of the far-receiving coil be |V2| and Φ2, respectively. Then we have:

[0051]

[0052] The amplitude ratio A and phase difference ΔΦ between the two receiving coils are defined as follows:

[0053]

[0054] Based on parameters such as the instrument's outer diameter, operating frequency, transmitter-receiver distance, and receiver-receiver distance, and following petroleum industry convention by setting the dielectric constant to a constant of 10 at two transmission frequencies, the phase difference and amplitude ratio values ​​for different formation conductivityes were calculated. Furthermore, since conductivity is inversely proportional to resistivity, the conversion relationship between formation resistivity and phase difference and amplitude ratio can be obtained, i.e., the theoretical chart, as shown below. Figure 3 , Figure 4 As shown in the diagram, interpolation calculations using this chart can yield the corresponding apparent resistivity value. Considering the limited underground storage space, the conversion from phase difference and amplitude ratio to resistivity is performed on the borehole computer. This apparent resistivity conversion saves underground storage space.

[0055] The power management unit supplies power to all components within the measuring instrument. It includes a high-efficiency DC-DC power module, an EMI filter module, a switching circuit, and a microcontroller. The high-voltage DC power input from the downhole battery is converted into the voltage required by the various circuit units of the instrument via the DC-DC power module. The EMI filter module removes switching noise to provide low-ripple DC power for the receiver unit and the signal processing, storage, and communication units. Simultaneously, the power output is controlled according to the instrument's operating mode to achieve power saving and low power consumption, extending battery life.

[0056] The measuring instrument has an outer diameter of 89mm, which meets the requirements for instrument outer diameter in most underground drilling measurements. The source distance is 30”≤L≤46”, the operating frequency is two specific frequencies between 0.4MHz and 5MHz, the total length is no more than 2m, and the distance between the two receiving antennas is 8”≤d≤14”. The short instrument length facilitates underground construction operations and reduces material and machining costs. The antennas employ magnetic loading technology, enhancing the received signal amplitude, reducing transmission power, extending underground battery life, and meeting the low-power transmission requirements of coal mines.

[0057] The instrument transmits two specific frequency electromagnetic wave signals through a transmitting antenna in a time-division manner. The signals propagate through the strata to two receiving antennas. By comparing the phase and amplitude of the two receiving antennas, the phase difference and amplitude ratio between the two receiving antennas at each frequency are obtained. These four sets of phase difference and amplitude ratios are transmitted to the host computer (wellhead receiver box) via mud pulse or wired connection, and then transmitted to the ground computer via USB cable. Through inversion, the resistivity data corresponding to the four sets of phase difference and amplitude ratios can be calculated. This resistivity data can reflect the changes in stratum lithology in real time.

Claims

1. A small diameter electromagnetic wave resistivity measurement tool for use in mining, characterized by: The non-magnetic drill collar is provided with a transmitter unit, a transmitting antenna, two receiver units, two receiving antennas, a signal processing, storage and communication unit and a power management unit; The transmitter unit comprises a microprocessor, a DDS circuit module, an elliptical filter module, a programmable gain amplification module, a radio frequency power amplification module and a dual-frequency matching network module which are electrically connected in sequence, and the dual-frequency matching network module is electrically connected with the transmitting antenna; The two receiver units are of the same structure and each comprises a front-end dual-frequency matching network, a low-noise amplifier, a mixing module and an intermediate frequency amplification filter module which are electrically connected in sequence, the front-end dual-frequency matching network is electrically connected with one receiving antenna, and the intermediate frequency amplification filter module is electrically connected with a double-channel high-speed AD acquisition module in the signal processing, storage and communication unit; The signal processing, storage and communication unit comprises a DSP module, a double-channel high-speed AD acquisition module, a large-capacity data storage module and a communication module which are electrically connected with the DSP module; The power management unit supplies power to each component in the measuring instrument.

2. The small diameter electromagnetic wave resistivity measurement instrument while drilling for mining according to claim 1, characterized in that: An annular antenna warehouse for placing an antenna coil and a square circuit board warehouse for placing a circuit board are formed on the outer wall of the non-magnetic drill collar, n wire holes are formed in the framework of the non-magnetic drill collar, and the middle of the non-magnetic drill collar is a mud flow channel.

3. The small diameter LWD EM wave resistivity tool of claim 2, wherein: A non-metallic framework with a certain thickness is installed in the antenna warehouse, a certain number of rectangular grooves are formed along the circumferential direction of the non-metallic framework, magnetic strips are inlaid into the rectangular grooves, a certain number of coils are wound on the non-metallic framework, and finally an antenna cover is covered and sealed with epoxy glue.

4. The small diameter electromagnetic wave resistivity measurement instrument while drilling for mining as claimed in claim 2, wherein: The antenna warehouse and the circuit board warehouse are electrically connected through a sealing plug warehouse; a read-write inspection port is further arranged on the outer wall of the non-magnetic drill collar.

5. The small diameter LWD EM wave resistivity tool of claim 1, wherein: The signal processing, storage and communication unit further comprises a clock management module and a PIC microprocessor module.

6. The small diameter electromagnetic wave resistivity measurement tool for use in a mine of claim 1, wherein: The power management unit comprises a DC-DC power module, an EMI filter module, a switching circuit and a microcontroller.

7. The small diameter electromagnetic wave resistivity measurement tool for use in a mine of claim 1, wherein: The measuring instrument has an outer diameter of 89 mm, a source distance of 30''≤L≤46'', a working frequency of two specific frequencies between 0.4 MHz and 5 MHz, a total length of not more than 2 m, and a distance between the two receiving antennas of 8''≤d≤14''.

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