Radio frequency shielding device and method for nuclear magnetic resonance logging
By setting an array shielding coil between the RF coil and the metal mud pipeline in the NMR log, and adjusting its parameters to resonate at the NMR frequency point, the problem of the signal-to-noise ratio reduction in the eddy current in the RF coil is solved, and more efficient eddy current suppression and signal measurement are achieved.
Patent Information
- Application Number
- CN202411840054.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2025-03-25
Smart Images
Figure CN119689585A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of nuclear magnetic resonance well logging, and in particular to a radio frequency shielding device and method for nuclear magnetic resonance well logging. Background Art
[0002] When a conductor is placed in a time-varying magnetic field, the magnetic field will induce eddy currents in the conductor. Therefore, when the radio frequency coil of nuclear magnetic resonance logging is working, eddy currents will be generated in the copper mesh shielding layer inside the radio frequency coil and the metal mud pipe inside the copper mesh shielding layer. Eddy currents have thermal and demagnetizing effects. The thermal effect will generate eddy current losses in the metal conductors inside the radio frequency coil (such as the copper mesh shielding layer and the metal mud channel), increase the equivalent AC resistance of the radio frequency coil, and thus reduce the signal-to-noise ratio of nuclear magnetic resonance measurement; at the same time, the demagnetization effect will weaken the radio frequency magnetic field generated by the radio frequency coil, so the presence of eddy currents will greatly reduce the signal-to-noise ratio of the radio frequency coil. Therefore, in order to improve the signal-to-noise ratio of the radio frequency coil of nuclear magnetic resonance logging, it is necessary to suppress the eddy currents generated by radio frequency as much as possible.
[0003] However, at present, there is no other RF suppression technology except sticking a copper mesh shielding layer, namely a mesh copper film, on the inner side of the RF coil. Moreover, the mesh copper film has limited eddy current suppression effect and cannot meet the requirements of measuring weak magnetic resonance signals in practice. Summary of the invention
[0004] In order to better reduce the eddy current generated by the radio frequency of the radio frequency coil of nuclear magnetic resonance logging, the present invention proposes a radio frequency shielding device and method for nuclear magnetic resonance logging.
[0005] The radio frequency shielding device for nuclear magnetic resonance logging according to the present invention comprises: an array shielding coil for being arranged between a radio frequency coil and a metal mud pipe, the array shielding coil comprising at least one array shielding coil layer, the array shielding coil layer comprising a flexible insulating substrate and a plurality of first metal coils distributed in an array on the front side of the flexible insulating substrate, and a plurality of second metal coils distributed in an array on the back side of the flexible insulating substrate and arranged opposite to each first metal coil, the first metal coil being electrically connected to the corresponding second metal coil.
[0006] Furthermore, the array shielding coil includes a plurality of array shielding coil layers, and each array shielding coil layer is bonded together.
[0007] Furthermore, the sizes and distribution patterns of the first metal coils and the second metal coils on the same array shielding coil layer are the same, and the sizes and distribution patterns of the first metal coils and the second metal coils on different array shielding coil layers are different.
[0008] Furthermore, the array shielding coil is pasted between the radio frequency coil and the metal slurry pipe.
[0009] Furthermore, the first metal coil and the second metal coil are both spiral-shaped, and the starting end and the ending end of the first metal coil are respectively connected to the starting end and the ending end of the corresponding second metal coil through vias.
[0010] Furthermore, the first metal coil and the second metal coil each include at least one inner coil and one outer coil located outside the inner coil.
[0011] Furthermore, the array shielding coil layer also includes an external inductor or capacitor connected between the starting end and the ending end of the first metal coil and / or connected between the starting end and the ending end of the second metal coil.
[0012] Furthermore, the material of the flexible insulating substrate is polyester amide.
[0013] According to the radio frequency shielding method for nuclear magnetic resonance logging of the present invention, the radio frequency shielding device for nuclear magnetic resonance logging is used, which includes: causing resonance to occur when the magnetic field emitted by the radio frequency coil propagates to the radio frequency shielding device.
[0014] Furthermore, the RF shielding method for nuclear magnetic resonance logging also includes: controlling the frequency of the array shielding coil by adjusting the number of turns, turn spacing, radius of the first metal coil and the second metal coil, and the thickness of the flexible insulating substrate, so that the frequency of the magnetic field emitted by the RF coil is the same as the frequency of the array shielding coil.
[0015] Compared with the prior art, although the mesh copper film arranged between the RF coil and the metal slurry pipe in the prior art can suppress eddy currents to a certain extent, the array shielding coil structure adopted by the RF shielding device of the present invention can theoretically realize an isolation shielding layer with infinite impedance, and the eddy current suppression effect is several times that of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 It is a planar development schematic diagram of the structure of a radio frequency shielding device for nuclear magnetic resonance logging according to an embodiment of the present invention;
[0017] Figure 2 A schematic diagram of a bent structure of a radio frequency shielding device for nuclear magnetic resonance logging according to an embodiment of the present invention;
[0018] Figure 3 The figure is a schematic diagram of the installation of a radio frequency shielding device for nuclear magnetic resonance logging according to an embodiment of the present invention. DETAILED DESCRIPTION
[0019] In order to better understand the purpose, structure and function of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.
[0020] Figure 1 and Figure 2 The structure of a radio frequency shielding device 2 for nuclear magnetic resonance logging according to an embodiment of the present invention is shown. Figure 3 The schematic diagram of the installation of the radio frequency shielding device 2 for nuclear magnetic resonance logging is shown. Figures 1 to 3 As shown, the radio frequency shielding device 2 for nuclear magnetic resonance logging may include: an array shielding coil for being arranged between the radio frequency coil 1 and the metal mud pipe 3, the array shielding coil may include at least one array shielding coil layer 20, the array shielding coil layer 20 may include a flexible insulating substrate 22 and a plurality of first metal coils 21 distributed in an array on the front side of the flexible insulating substrate 22, and a plurality of second metal coils distributed in an array on the back side of the flexible insulating substrate 22 and arranged opposite to the first metal coils (not shown in the figure), the first metal coil 21 is electrically connected to the corresponding second metal coil.
[0021] In the radio frequency shielding device 2 for nuclear magnetic resonance logging in the embodiment of the present invention, the first metal coil 21 and the second metal coil are conductors themselves, and therefore have a certain resistance. At the same time, the first metal coil 21 and the second metal coil themselves form an inductance of a certain size. The first metal coil 21 and the second metal coil are made of metal conductor materials, and the flexible insulating substrate 22 located between the two is an insulating material. In this way, the metal conductor-insulating medium-metal conductor forms a capacitor. The first metal coil 21 and the corresponding second metal coil are arranged one by one and electrically connected. Therefore, for any pair of the first metal coil 21 and the second metal coil, the resistance and inductance of the first metal coil 21 are connected in series to form a first circuit, the resistance and inductance of the second metal coil are connected in series to form a second circuit, and the capacitor is connected in parallel between the first circuit and the second circuit, so that a complete resonant circuit is formed. The resistance and inductance values can be precisely controlled by controlling the number of turns, turn spacing and radius of the first metal coil 21 and the second metal coil, and the capacitance can be precisely controlled by controlling the thickness of the flexible insulating substrate 22, so that the array shielding coil can resonate at the nuclear magnetic resonance frequency point (i.e., the RF frequency of the RF coil 1). When resonating, the array shielding coil will exhibit an infinite impedance characteristic, which is equivalent to inserting an infinite impedance isolation layer between the RF coil 1 and the metal slurry pipe 3. Due to the large impedance, the amplitude of the eddy current is greatly reduced, thereby playing a better role in suppressing the eddy current.
[0022] In a preferred embodiment, the array shielding coil may include a plurality of array shielding coil layers 20, and each array shielding coil layer 20 is bonded together. One array shielding coil layer 20 corresponds to one nuclear magnetic resonance frequency point, and by providing a plurality of array shielding coil layers 20, the array shielding coil can correspond to a plurality of nuclear magnetic resonance frequency points, so that the array shielding coil has a multi-frequency resonance point.
[0023] Preferably, the first metal coil 21 and the second metal coil on the same array shielding coil layer 20 have the same size and distribution pattern to facilitate the manufacture of the same array shielding coil layer 20, and the first metal coil 21 and the second metal coil on different array shielding coil layers 20 have different sizes and distribution patterns to make the frequency adjustable ranges corresponding to different frequency resonance points different.
[0024] In such Figure 3 In the preferred embodiment shown, the array shielding coil can be fixed between the radio frequency coil 1 and the metal slurry pipe 3 by gluing.
[0025] In such Figure 1 and Figure 2 In the preferred embodiment shown, both the first metal coil 21 and the second metal coil can be spiral-shaped, and the starting end and the end of the first metal coil 21 are respectively connected to the starting end and the end of the corresponding second metal coil through vias (not shown in the figure). This setting is used to achieve electrical connection between the first metal coil 21 and the corresponding second metal coil.
[0026] Furthermore, in Figure 1 In the preferred embodiment shown, both the first metal coil 21 and the second metal coil may include at least one inner ring 211 and one outer ring 212 outside the inner ring 211. In this embodiment, a flexible insulating substrate is provided between the inner ring 211 and the outer ring 212, so the inner ring 211, the outer ring 212 and the flexible insulating substrate can still form a capacitor, thus forming a plurality of resonant circuits distributed in a plane on both the front and back sides of the flexible insulating substrate 22. In other words, the first metal coil 21 and the second metal coil themselves and between the first metal coil 21 and the corresponding second metal coil can form a distribution of resonant circuits, and such a setting is conducive to more accurately controlling the size of resistance, inductance and capacitance, so that the array shielding coil resonates at the nuclear magnetic resonance frequency point.
[0027] In a preferred embodiment, when the inductance and capacitance of the first metal coil 21 and / or the second metal coil on the array shielding coil layer 20 do not meet the resonance condition, the array shielding coil layer 20 may further include an external inductor or capacitor connected between the starting end and the end of the first metal coil 21, and / or connected between the starting end and the end of the second metal coil, so that the array shielding coil meets the required resonance condition.
[0028] In a preferred embodiment, the material of the flexible insulating substrate 22 may be polyester amide.
[0029] According to the radio frequency shielding method for nuclear magnetic resonance logging according to the embodiment of the present invention, the radio frequency shielding device 2 for nuclear magnetic resonance logging described above may include: causing resonance to occur when the magnetic field emitted by the radio frequency coil 1 propagates to the radio frequency shielding device 2. In this way, the radio frequency shielding device 2 will present an infinite impedance feature during resonance, which is equivalent to inserting an infinite impedance isolation layer between the radio frequency coil 1 and the metal slurry pipe 3. Due to the large impedance, the amplitude of the eddy current is greatly reduced, thereby playing a role in better suppressing the eddy current.
[0030] In a preferred embodiment, the RF shielding method for nuclear magnetic resonance logging may also include: controlling the frequency of the array shielding coil by adjusting the number of turns, turn spacing, radius of the first metal coil 21 and the second metal coil, and the thickness of the flexible insulating substrate 22, so that the frequency of the magnetic field emitted by the RF coil 1 is the same as the frequency of the array shielding coil, thereby achieving the purpose of resonance on the RF shielding device 2.
[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various 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 that fall within the scope of the claims.
Claims
1. A radio frequency shielding device for nuclear magnetic resonance logging, characterized in that: include: An array shielding coil for being arranged between a radio frequency coil and a metal slurry pipeline, the array shielding coil comprising at least one array shielding coil layer, the array shielding coil layer comprising a flexible insulating substrate and a plurality of first metal coils distributed in an array on the front side of the flexible insulating substrate, and a plurality of second metal coils distributed in an array on the back side of the flexible insulating substrate and arranged opposite to each of the first metal coils, the first metal coils being electrically connected to the corresponding second metal coils.
2. The radio frequency shielding device for nuclear magnetic resonance logging according to claim 1, characterized in that: The array shielding coil comprises a plurality of array shielding coil layers, and each of the array shielding coil layers is bonded together.
3. The radio frequency shielding device for nuclear magnetic resonance logging according to claim 2, characterized in that: The sizes and distribution patterns of the first metal coil and the second metal coil on the same array shielding coil layer are the same, and the sizes and distribution patterns of the first metal coil and the second metal coil on different array shielding coil layers are different.
4. The radio frequency shielding device for nuclear magnetic resonance logging according to any one of claims 1 to 3, characterized in that: The array shielding coil is pasted between the radio frequency coil and the metal slurry pipe.
5. The radio frequency shielding device for nuclear magnetic resonance logging according to any one of claims 1 to 3, characterized in that: The first metal coil and the second metal coil are both spiral-shaped, and a starting end and an ending end of the first metal coil are respectively connected to a corresponding starting end and an ending end of the second metal coil through vias.
6. The radio frequency shielding device for nuclear magnetic resonance logging according to claim 5, characterized in that: The first metal coil and the second metal coil each include at least one inner coil and one outer coil located outside the inner coil.
7. The radio frequency shielding device for nuclear magnetic resonance logging according to claim 5, characterized in that: The array shielding coil layer further includes an external inductor or capacitor connected between a starting end and an end of the first metal coil and / or connected between a starting end and an end of the second metal coil.
8. The radio frequency shielding device for nuclear magnetic resonance logging according to any one of claims 1 to 3, characterized in that: The material of the flexible insulating substrate is polyester amide.
9. A radio frequency shielding method for nuclear magnetic resonance logging, using the radio frequency shielding device for nuclear magnetic resonance logging according to any one of claims 1 to 8, characterized in that: include: The magnetic field emitted by the radio frequency coil is made to resonate when it propagates to the radio frequency shielding device.
10. The radio frequency shielding method for nuclear magnetic resonance logging according to claim 9, characterized in that: Also includes: The frequency of the array shielding coil is controlled by adjusting the number of turns, the turn spacing, the radius of the first metal coil and the second metal coil, and the thickness of the flexible insulating substrate, so that the frequency of the magnetic field emitted by the radio frequency coil is the same as the frequency of the array shielding coil.