Nuclear magnetic resonance double-saddle-shaped radio frequency coil for logging while drilling

Abstract

The invention belongs to the technical field of nuclear magnetic resonance logging, and discloses a nuclear magnetic resonance double-saddle-shaped radio frequency coil for logging while drilling. The nuclear magnetic resonance double-saddle-shaped radio frequency coil for well logging while drilling comprises two symmetrical saddle-shaped coils, each saddle-shaped coil is in a saddle shape, and the two saddle-shaped coils are arranged in a space perpendicular to each other or arranged in parallel at an interval. According to the nuclear magnetic resonance double-saddle-shaped radio frequency coil for well logging while drilling, the signal-to-noise ratio of the nuclear magnetic resonance well logging radio frequency coil can be effectively improved, and therefore stratum measurement can be more effectively carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear magnetic resonance logging, and particularly relates to a nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling. Background Art

[0002] In nuclear magnetic resonance logging, the radio frequency coil is a key component for realizing formation measurement. As Figure 4 shown, most of the existing nuclear magnetic logging radio frequency coils adopt a solenoid coil structure. However, after being energized with an excitation current, the radio frequency magnetic field strength in the target area is relatively low, resulting in insufficient detection sensitivity, which in turn affects the signal-to-noise ratio of nuclear magnetic resonance logging. Specifically, as Figure 5 and Figure 6 shown, the maximum radio frequency magnetic field value of the existing solenoid coil in the target area is only 0.00116T, which is difficult to meet the requirements of high-precision formation measurement. Summary of the Invention

[0003] The present invention aims to propose a double-saddle radio frequency coil structure to improve the signal-to-noise ratio of the radio frequency coil for nuclear magnetic resonance logging, so as to be able to perform formation measurement more effectively.

[0004] The nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling according to the present invention includes: two symmetric saddle-shaped coils, each saddle-shaped coil has a saddle shape, and the two saddle-shaped coils are arranged perpendicular to each other or parallel and spaced apart in space.

[0005] Further, the wire of the saddle-shaped coil adopts a stranded wire.

[0006] Further, the number of turns of the saddle-shaped coil is 5 - 20 turns.

[0007] Further, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling further includes a support structure for fixing the saddle-shaped coil, and the support structure is made of a high-strength insulating material.

[0008] Further, the excitation current frequency range of the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling is 1 MHz - 20 MHz.

[0009] Further, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling further includes a signal processing module for amplifying, filtering, and digitizing the collected nuclear magnetic resonance signals, and an interface module for connecting to the logging while drilling system. The interface module is used to transmit the signals processed by the signal processing module to the ground control unit.

[0010] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling further includes a magnetic field intensity monitoring unit, which is used to monitor the radio frequency magnetic field intensity in the target area in real time and feed the monitoring data back to the ground control unit. The ground control unit dynamically adjusts the parameters of the excitation current according to the feedback data.

[0011] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling further includes a temperature compensation module, which is used to monitor the temperature change of the working environment of the saddle-shaped coil in real time and feed the monitoring data back to the ground control unit. The ground control unit automatically adjusts the parameters of the excitation current according to the temperature change.

[0012] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling further includes a self-calibration module, which is used to automatically detect the magnetic field intensity and uniformity of the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling before each logging operation, and automatically adjust the parameters of the saddle-shaped coil according to the detection results.

[0013] Furthermore, an electromagnetic shielding layer is arranged between the two saddle-shaped coils. The electromagnetic shielding layer is made of a highly conductive material and is used to reduce the electromagnetic coupling between the two saddle-shaped coils.

[0014] Compared with the prior art, the nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling of the present invention has the following advantages:

[0015] 1) Under the same excitation current, the maximum radio frequency magnetic field value in the target area of the double-saddle coil of the present application can reach 0.0028T, which is more than twice that of the traditional coil. At the same time, through the optimized geometric structure, the double-saddle coil can form a more uniform magnetic field distribution in the target area, reduce magnetic field distortion, and the stronger and more uniform magnetic field can significantly improve the intensity and quality of the nuclear magnetic resonance signal, thus greatly improving the signal-to-noise ratio (SNR) and measurement accuracy;

[0016] 2) The structural design of the double-saddle coil doubles its detection sensitivity compared with the traditional solenoid coil. The stronger magnetic field and more uniform distribution enable the coil to more effectively excite the hydrogen nuclei in the formation, thus generating a stronger nuclear magnetic resonance signal;

[0017] 3) The double-saddle coil optimizes the three-dimensional coverage of the magnetic field through vertical or parallel arrangements. This design can more effectively excite and detect the nuclear magnetic resonance signal in the formation. Especially in complex formations, the optimized magnetic field coverage and measurement accuracy enable the present application to provide more comprehensive and accurate formation information, providing a more reliable basis for oil and gas exploration and development;

[0018] 4) The double-saddle coil can generate a stronger magnetic field under the same excitation current, reducing the measurement time and energy consumption. At the same time, its high signal-to-noise ratio and high sensitivity reduce the need for repeated measurements, thus significantly improving the measurement efficiency and reducing the operation cost. It is especially suitable for time-sensitive application scenarios such as logging while drilling.

[0019] 5) By optimizing the geometric structure and electromagnetic shielding design of the double-saddle coil, external electromagnetic interference can be effectively reduced. At the same time, its signal processing module can amplify, filter, and digitize the collected signals, further improving the signal quality. The enhanced anti-interference ability and high signal quality enable this application to work stably in complex downhole environments and provide reliable measurement data.

[0020] 6) The size, shape, and number of turns of the double-saddle coil can be customized according to the outer diameter and measurement depth of the logging tool. In addition, its excitation current frequency range is 1 MHz - 20 MHz, which can be adjusted according to different formation characteristics.

[0021] 7) The double-saddle coil uses multi-strand stranded wire, which has higher flexibility and fracture resistance. At the same time, its support structure is made of high-strength insulating materials, which can effectively reduce the influence of mechanical vibration and chemical corrosion, reduce the maintenance cost and replacement frequency of the coil, and improve the continuity and economic benefits of logging operations.

[0022] 8) The double-saddle coil is equipped with a magnetic field strength monitoring unit, a temperature compensation module, and a self-calibration module, which can monitor the working state of the coil in real time and automatically adjust the excitation current parameters to ensure the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a schematic structural diagram of a nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling according to an embodiment of the present invention;

[0024] Figure 2 FIG. is a radio frequency magnetic field vector diagram of a nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling according to an embodiment of the present invention;

[0025] Figure 3 FIG. is a radio frequency magnetic field contour diagram of a nuclear magnetic resonance double-saddle radio frequency coil for logging while drilling according to an embodiment of the present invention;

[0026] Figure 4 FIG. is a schematic structural diagram of a solenoid coil of the prior art;

[0027] Figure 5 FIG. is a radio frequency magnetic field vector diagram of a solenoid coil of the prior art;

[0028] Figure 6 FIG. is a radio frequency magnetic field contour diagram of a solenoid coil of the prior art. Detailed implementation manners

[0029] To better understand the purpose, structure and function of the present invention, the following further describes the present invention in detail with reference to the accompanying drawings.

[0030] Figure 1 Shows the structure of the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling according to an embodiment of the present invention. As Figure 1 shown, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling includes two symmetric saddle-shaped coils 1. The shape of each saddle-shaped coil 1 is saddle-shaped, and the two saddle-shaped coils 1 are arranged perpendicular to each other or parallel and spaced apart in space.

[0031] In the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling according to an embodiment of the present invention, by using the saddle-shaped coil 1, its wire is curved and is usually symmetrically distributed around a central axis. This shape enables the coil to generate a stronger and more uniform radio frequency magnetic field in the target area. The geometric structure of the saddle-shaped coil can convert current into magnetic field more effectively, reduce energy loss, and make the magnetic field strength in the target area significantly higher than that of the traditional solenoid coil. The stronger magnetic field can more effectively excite hydrogen nuclei (protons) in the formation, thereby generating a stronger nuclear magnetic resonance signal. At the same time, the curved shape of the saddle-shaped coil 1 can better control the distribution of the magnetic field and reduce the edge effect. This design makes the magnetic field more concentrated in the target area, reduces the diffusion and distortion of the magnetic field, improves the uniformity of the magnetic field and the purity of the signal, thereby improving the signal-to-noise ratio. According to the reciprocity theorem of the antenna, the transmitting and receiving characteristics of the coil are interrelated. The saddle-shaped coil can generate a stronger magnetic field when transmitting the radio frequency magnetic field and can also more sensitively detect weak nuclear magnetic resonance signals when receiving signals, enabling it to more effectively capture the nuclear magnetic resonance signals in the formation when receiving signals, reduce signal attenuation and loss, and thereby improve the signal-to-noise ratio. In addition, the geometric shape of the saddle-shaped coil can better shield external electromagnetic interference. Due to its curved shape, the magnetic field inside the coil is relatively enclosed, reducing the interference of the external electromagnetic field on the measurement signal, thereby reducing electromagnetic interference, significantly reducing the background noise level, making the nuclear magnetic resonance signal clearer, and helping to further improve the signal-to-noise ratio.

[0032] When two saddle-shaped coils 1 are arranged perpendicular to each other, their magnetic field directions are also perpendicular to each other, thus forming a more uniform three-dimensional magnetic field distribution in the target area. This uniform magnetic field distribution can not only more effectively excite hydrogen nuclei (protons) in the formation, improve the quality and consistency of nuclear magnetic resonance signals, and reduce signal distortion caused by magnetic field inhomogeneity, but also effectively detect minute changes in the formation, thus better adapting to the heterogeneity of complex formations. At the same time, the vertically arranged double saddle-shaped coils 1 can generate a stronger synthetic magnetic field in the target area. Since the magnetic fields of the two coils are superimposed on each other, the magnetic field strength in the target area is significantly enhanced. A stronger magnetic field can increase the intensity of nuclear magnetic resonance signals, thereby enhancing the detection sensitivity. At the same excitation current, the double saddle-shaped coils can generate a higher magnetic field strength than traditional solenoid coils, significantly improving the signal-to-noise ratio (SNR). In addition, the saddle-shaped coils 1 arranged perpendicular to each other can detect nuclear magnetic resonance signals in multiple directions and excite and detect nuclear magnetic resonance signals in multiple directions, thus providing more comprehensive formation information and signal anisotropy. This design can not only more accurately measure parameters such as porosity, permeability, and fluid content of the formation, especially in complex formations (such as fractured formations, low-porosity formations), it can more effectively detect fluid signals in minute pores and fractures, improve the measurement accuracy, but also improve the quality and consistency of signals, reduce errors caused by signal directionality, and thus improve the usability and reliability of logging data. Moreover, the vertically arranged saddle-shaped coils 1 can reduce the edge effect and distortion of the magnetic field. Since the magnetic fields of the two coils compensate each other, the magnetic field distribution in the target area is more uniform, so the magnetic field distortion common in traditional solenoid coils is reduced. Reducing magnetic field distortion can improve the quality and stability of signals, reduce measurement errors caused by magnetic field inhomogeneity, and thus improve the reliability of logging data.

[0033] When two saddle-shaped coils 1 are arranged in parallel at intervals in the same plane, their magnetic field directions are the same, and the magnetic field intensities will be superimposed on each other within the target area. This design can generate a stronger synthetic magnetic field in a specific direction, thereby increasing the intensity of the nuclear magnetic resonance signal and enhancing the detection sensitivity. Compared with a single coil, the magnetic field intensity of the dual-coil is significantly increased, which can more effectively excite the hydrogen nuclei in the formation and improve the signal-to-noise ratio (SNR). At the same time, the two saddle-shaped coils 1 arranged at intervals in the same plane can measure the target area simultaneously, reducing the measurement time and the need for repeated operations. Especially in the logging-while-drilling scenario where rapid data acquisition is required, it can effectively shorten the operation time and reduce the logging cost. In addition, the two saddle-shaped coils 1 arranged at intervals in the same plane can not only detect nuclear magnetic resonance signals from different positions, thereby providing more signal samples, and through the superposition and comparison of signals, the noise interference can be reduced, the purity and consistency of the signals can be improved, and thus the reliability of the logging data can be enhanced. It can also excite and detect nuclear magnetic resonance signals from different directions, thereby better adapting to the anisotropy of the formation. This design can more accurately reflect the physical properties of the formation. Especially in fractured formations or formations with strong anisotropy, it can provide more comprehensive formation information to help more accurately evaluate the reservoir capacity and fluid properties of the formation. Moreover, the coils arranged at intervals in the same plane not only have a relatively simple structure and lower manufacturing process requirements. This design reduces the manufacturing cost and complexity, and at the same time is convenient for installation and maintenance. For some cost-sensitive application scenarios, this design has significant advantages. It also enables the other coil to continue to work even if one coil fails, improving the reliability and fault tolerance of the system and reducing the risk of logging interruption caused by a single coil failure.

[0034] Preferably, when two saddle-shaped coils 1 are arranged at intervals in the same plane, the distance and relative position between the coils can be adjusted to optimize the magnetic field uniformity to reduce magnetic field distortion and edge effects, thereby improving the measurement accuracy and signal quality. The signals detected by the two coils can also be compared and corrected through signal processing algorithms, which can effectively reduce the influence of external electromagnetic interference and improve the stability and reliability of the signals. Especially in a complex downhole environment, it can ensure the accuracy of the logging data.

[0035] Combined Figure 2 、 Figure 3 、 Figure 5 and Figure 6 As shown, when the dual saddle-shaped coil 1 is applied with the same excitation current, the maximum radio frequency magnetic field value within the target area is 0.0028T, which is twice that of the existing solenoid coil (the maximum radio frequency magnetic field value is 0.00116T); the structural design of the dual saddle-shaped coil 1 makes its detection sensitivity twice that of the existing solenoid coil.

[0036] In a preferred embodiment, the wire of the saddle-shaped coil 1 can be a stranded wire. Compared with a single-strand wire, the stranded wire has a lower resistance, reduces energy loss, and improves the efficiency of the coil. Moreover, the stranded wire has better flexibility, can adapt to complex downhole environments and the shape changes of logging tools, and reduces damage caused by mechanical stress. In addition, the structure of the stranded wire makes the coil less likely to break when subjected to mechanical stress, improving the durability and reliability of the coil.

[0037] Furthermore, the number of turns of the saddle-shaped coil 1 is 5 - 20 turns. By optimizing the number of turns, the double-saddle-shaped coil 1 can generate a stronger magnetic field in the target area, thereby improving the detection sensitivity. The specific number of turns can be adjusted according to the logging depth and formation characteristics, enabling the coil to achieve optimal performance in different application scenarios. Reasonable design of the number of turns can reduce energy consumption while ensuring performance, and improve the energy efficiency ratio of the coil.

[0038] In a preferred embodiment, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling further includes a support structure (not shown in the figure) for fixing the saddle-shaped coil 1. The support structure 1 can be made of a high-strength insulating material to ensure the stability and reliability of the coil during logging while drilling. Preferably, the support structure can be made of a composite material. The composite material has high strength, low density, and good electromagnetic shielding performance, can effectively reduce the influence of mechanical vibration on the coil performance, and at the same time reduce the weight of the coil. Further preferably, a wear-resistant coating can be provided on the surface of the support structure of the double-saddle-shaped coil 1. The wear-resistant coating can be made of a nanocomposite material, has high hardness and low friction coefficient, and can effectively reduce the wear of the coil during logging while drilling, extending the service life of the coil.

[0039] In a preferred embodiment, the excitation current frequency range of the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling can be 1 MHz - 20 MHz. By selecting an appropriate excitation frequency, it is possible to more accurately excite the hydrogen nuclei in the formation and improve the quality of the measurement data. The adjustable frequency design enables the coil to adapt to a variety of logging tasks, improving the versatility of the equipment.

[0040] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling may further include a signal processing module (not shown in the figure), which is used to amplify, filter, and digitize the acquired nuclear magnetic resonance signals to improve the signal quality and usability, and an interface module (not shown in the figure) for connecting to the logging while drilling system. The interface module is used to transmit the signals processed by the signal processing module to the ground control unit. The signals processed by the signal processing module are clearer, easier to analyze and interpret, reduce the complexity of data processing, and improve the reliability of logging results. The interface module can efficiently transmit the processed signals to the ground control unit without large-scale modification of existing equipment, reducing the cost of technology update.

[0041] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling may further include a magnetic field intensity monitoring unit (not shown in the figure), which is used to monitor the radio frequency magnetic field intensity in the target area in real time and feedback the monitoring data to the ground control unit. The ground control unit dynamically adjusts the parameters of the excitation current according to the feedback data to optimize the magnetic field intensity and uniformity. Through real-time monitoring and adjustment, magnetic field anomalies can be detected in a timely manner, reducing measurement errors caused by insufficient or non-uniform magnetic field intensity, so as to ensure that the magnetic field intensity is always in the best state and improve the accuracy of measurement data.

[0042] Preferably, the parameters of the excitation current may include the amplitude, frequency, phase, pulse width, repetition frequency, etc. of the excitation current.

[0043] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling may further include a temperature compensation module (not shown in the figure), which is used to monitor the temperature change of the working environment of the saddle coil 1 in real time and feedback the monitoring data to the ground control unit. The ground control unit automatically adjusts the parameters of the excitation current according to the temperature change to ensure the magnetic field intensity and signal stability of the coil under different temperature conditions. Through temperature compensation, measurement errors caused by temperature changes can be reduced, and the accuracy of logging data can be improved.

[0044] Furthermore, the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling may further include a self-calibration module (not shown in the figure), which is used to automatically detect the magnetic field intensity and uniformity of the nuclear magnetic resonance double-saddle radio frequency coil 100 for logging while drilling before each logging operation starts, and automatically adjust the parameters of the saddle coil according to the detection results to ensure the accuracy of the measurement results. Automated calibration reduces human operation errors and improves the reliability, consistency, and operation efficiency of logging operations.

[0045] Preferably, the parameters of the coil may include the number of turns, wire material, size, inductance, and capacitance, etc.

[0046] In a preferred embodiment, an electromagnetic shielding layer may be provided between two saddle coils 1. The electromagnetic shielding layer may be made of a highly conductive material and is used to reduce the electromagnetic coupling between the two saddle coils 1. The shielding layer made of the highly conductive material can effectively reduce external electromagnetic interference and improve the stability and reliability of the signal. By reducing electromagnetic coupling and interference, the nuclear magnetic resonance signal in the formation can be detected more accurately, improving the measurement accuracy.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the specification of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A nuclear magnetic resonance double saddle radio frequency coil for logging while drilling, characterized in that: The invention comprises two symmetrical saddle-shaped coils, each of which is in the shape of a saddle, and the two saddle-shaped coils are arranged vertically or parallelly with each other in space.

2. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1, characterized in that: The conductor of the saddle coil is a multi-strand twisted wire.

3. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: The number of turns of the saddle coil is 5-20 turns.

4. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: The nuclear magnetic resonance double saddle-shaped radio frequency coil for logging while drilling also includes a support structure for fixing the saddle-shaped coil, and the support structure is made of high-strength insulating material.

5. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: The excitation current frequency range of the nuclear magnetic resonance double saddle radio frequency coil used for logging while drilling is 1 MHz-20 MHz.

6. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling also includes a signal processing module for amplifying, filtering and digitally processing the collected nuclear magnetic resonance signals, and an interface module for connecting to the logging while drilling system, wherein the interface module is used to transmit the signal processed by the signal processing module to a ground control unit.

7. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 6, characterized in that: The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling also includes a magnetic field strength monitoring unit, which is used to monitor the radio frequency magnetic field strength in the target area in real time and feed back the monitoring data to the ground control unit, and the ground control unit dynamically adjusts the parameters of the excitation current according to the feedback data.

8. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 7, characterized in that: The nuclear magnetic resonance double saddle RF coil for logging while drilling also includes a temperature compensation module for real-time monitoring of temperature changes in the working environment of the saddle coil and feeding back the monitoring data to the ground control unit, which automatically adjusts the parameters of the excitation current according to the temperature changes.

9. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: The nuclear magnetic resonance dual saddle RF coil for logging while drilling also includes a self-calibration module, which is used to automatically detect the magnetic field strength and uniformity of the nuclear magnetic resonance dual saddle RF coil for logging while drilling before each logging operation begins, and automatically adjust the parameters of the saddle coil according to the detection results.

10. The nuclear magnetic resonance double saddle radio frequency coil for logging while drilling according to claim 1 or 2, characterized in that: An electromagnetic shielding layer is arranged between the two saddle coils. The electromagnetic shielding layer is made of a highly conductive material and is used to reduce the electromagnetic coupling between the two saddle coils.

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