Downhole borehole nuclear magnetic resonance detection device and working method

Abstract

The present invention belongs to the field of rock and soil detection, and provides a downhole borehole nuclear magnetic resonance detection device and working method. The device includes a transmitting system, a transmitting coil, a receiving system, a receiving probe, a control system and a processor; the control system is connected to the transmitting system and the receiving system respectively; the transmitting system is connected to the transmitting coil, which is arranged on the face of the tunnel and is used to transmit a pulse signal of set frequency and amplitude; the receiving system is connected to the receiving probe, which is arranged in the borehole of the face of the tunnel and is used to collect the echo signal of the pulse signal and transmit it to the processor through the receiving system; the processor is used to obtain the detection result data according to the echo signal and analyze the imaging to identify the groundwater source.

Description

Technical Field

[0001] The invention belongs to the field of rock and soil detection, and in particular relates to a downhole borehole nuclear magnetic resonance detection device and a working method. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid development of mine engineering construction, in underground mines, especially deep mines, groundwater is over-compressed, generating great hydraulic pressure, which is very likely to cause serious water inrush disasters. In coal mines, water disasters have become the second biggest problem threatening production safety after gas explosions. In non-coal mines, water disasters are the first biggest problem threatening mine production safety. Therefore, the mine advanced geological prediction method should not only be able to detect the spatial location of the disaster water source, but also put forward higher requirements on the prediction method in terms of water detection accuracy and water content within the detection range. The response signal detected by the nuclear magnetic resonance method is directly related to the size of the water body, and can directly detect the water content of the formation.

[0004] Nuclear magnetic resonance advance detection technology uses a transmitting coil to provide a high-power sinusoidal alternating current pulse with a Larmor frequency to generate an excitation magnetic field, which causes the hydrogen protons in the water to undergo nuclear magnetic resonance. After the excitation stops, the receiving system receives the induced electromagnetic signal, from which information such as the height of the groundwater level, the water content and porosity of the aquifer and other stratum structural information can be obtained, and the water body condition in front of the coil can be detected.

[0005] The inventors have found that traditional downhole nuclear magnetic resonance measurements are limited by extreme environmental conditions underground, and cannot fully play a guiding role in exploration and development in terms of measurement resolution, accuracy, and detection depth. Specifically, there are the following problems: (1) The space in the well is small, and the space for laying coils is also very limited. The side length of the coil laid in the tunnel cannot be greater than 6 meters, which is not conducive to transmission and reception. The distance of nuclear magnetic resonance advance detection is very limited. (2) Metal materials such as steel arches and steel mesh in the well will have a great impact on the magnetic field distribution of the excitation source, and at the same time make the detection coil resistance larger and the inductance smaller, which indirectly affects the transmission frequency. (3) The noise components in the well are chaotic. In the case of strong electromagnetic interference, weak signal detection is also a big problem. (4) Detection coil types include the same coil and separate coil. The transmitting coil and the receiving coil use the same coil in time-sharing mode, and the same coil mobile measurement mode is adopted. The resolution and work efficiency are very low, and the workload is large for covering a large area. The separate coil consists of a transmitting coil and one (or more) receiving coils of the same size. Multiple receiving coils can significantly increase the amount of data and the amount of information in the measurement results, but the transmitting coil needs to be transmitted in rotation, which cannot reduce the number of measurements, that is, the measurement efficiency is still very low. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned background technology, the first aspect of the present invention provides a downhole borehole nuclear magnetic resonance detection device, which adopts a detection method of transmitting at the face and receiving at the borehole, which can solve the problem of shallow axial detection depth of nuclear magnetic resonance wellbore to a certain extent and improve the longitudinal resolution.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A downhole borehole nuclear magnetic resonance detection device, comprising a transmitting system, a transmitting coil, a receiving system, a receiving probe, a control system and a processor;

[0009] The control system is connected to the transmitting system and the receiving system respectively;

[0010] The transmitting system is connected to a transmitting coil, which is arranged on the face of the tunnel and is used to transmit a pulse signal of a set frequency and amplitude;

[0011] The receiving system is connected to a receiving probe, which is arranged in a borehole of the tunnel face and is used to collect the echo signal of the pulse signal and transmit it to the processor via the receiving system;

[0012] The processor is used to obtain detection result data according to the echo signal and analyze the image to identify the underground water source.

[0013] As an implementation manner, the borehole is spaced apart from the outer edge of the transmitting coil by a first set distance, and adjacent boreholes are spaced apart by a second set distance.

[0014] As an implementation manner, the processor includes a data input module, a preprocessing module, an inversion processing module and an image output module which are connected in sequence.

[0015] As an implementation mode, the transmitting system includes a tank circuit, a power amplifier circuit and a transmitting circuit connected in sequence, and the moiré frequency when the transmitting circuit transmits a maximum transmitting current matches the capacitance value of the tuning capacitor.

[0016] As an implementation mode, the receiving system includes an isolation circuit, a preamplifier circuit, a filter amplifier circuit and an acquisition circuit which are connected in sequence, and an input end of the isolation circuit is connected to a receiving probe.

[0017] As an implementation manner, the transmitting coil is in a square shape.

[0018] As an implementation manner, the transmitting coil is laid on a coil support, and the coil support is fixed on the tunnel face.

[0019] As an implementation manner, the receiving probe is a permanent magnetic probe.

[0020] As an embodiment, the receiving probe includes a wall-attached probe and a centered probe, both of which include a magnet, an antenna, a shell and a frame, and the magnet, antenna and frame are all arranged inside the shell; the frame in the centered probe is in the center of the probe, and the magnet and antenna are arranged outside the frame; the magnet and antenna of the wall-attached probe are respectively located on the left and right sides of the probe.

[0021] As an implementation mode, the receiving probe is also connected to a probe transmission system, and the probe transmission system is used to carry the receiving probe and receive and transmit the receiving probe in the borehole.

[0022] As an embodiment, the probe transmission system includes a protective sleeve, a receiving and sending rod barrel, a cable and a probe fixing device. The receiving probe is connected to the receiving system via a cable, and the cable is arranged inside the receiving and sending rod barrel. Protrusions are provided on both sides of the outer wall of the receiving and sending rod barrel. The protective sleeve is sleeved on the outside of the receiving and sending rod barrel, and the inner wall of the protective sleeve is provided with grooves corresponding to the protrusions. The probe fixing device is arranged on the upper part of the protective sleeve.

[0023] A second aspect of the present invention provides a working method of a downhole borehole nuclear magnetic resonance detection device, comprising:

[0024] According to the size and shape of the tunnel face, advance drilling and deployment of transmitting coils are carried out on the tunnel face;

[0025] Connecting to the downhole borehole nuclear magnetic resonance detection device as described above;

[0026] Adjust the moiré frequency so that the moiré frequency at the maximum transmitting current matches the capacitance value of the tuning capacitor;

[0027] The control system sends a signal to the transmitting system, and the transmitting system starts to transmit pulses through the transmitting coil. After the transmission stops and the energy discharge is completed, the control system sends a collection signal to the receiving system. The receiving system transmits the collected echo signal to the processor to obtain the detection result data and analyze and image it, finally completing the identification of the groundwater source.

[0028] The beneficial effects of the present invention are:

[0029] (1) The present invention adopts a detection method of transmitting at the face and receiving at the borehole, which solves the problem of shallow axial detection depth of nuclear magnetic resonance wellbore to a certain extent, increases the detection depth, improves the longitudinal resolution, reduces the interference of construction machinery in the well on the detection, and improves the accuracy and reliability of the detection. The space in the well is small, and the observation device for receiving at the borehole is used to improve the space utilization rate of well detection.

[0030] (2) The array receiving method of the present invention, which uses a combination of a centered receiving probe and a wall-mounted magnetic probe, can expand the receiving area, significantly enhance the ability to resolve weak signals, greatly improve the signal-to-noise ratio, and easily perform backward shielding, thus achieving one-transmit-multiple-receive. Only one transmission is required to obtain signals at multiple locations, which can reduce the number of measurements and improve detection efficiency.

[0031] (3) The present invention adopts a positioning and directional positioning device of the receiving and sending rod barrel protrusion and the protective sleeve groove to effectively avoid collision loss of the receiving probe and provide a certain safety distance for the receiving probe.

[0032] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 is a block diagram of a downhole borehole nuclear magnetic resonance detection device according to an embodiment of the present invention;

[0035] FIG. 2( a ) is a schematic diagram of the structure of a central receiving probe arranged underground in an embodiment of the present invention;

[0036] FIG2( b ) is a schematic diagram of the structure of a wall-attached probe arranged underground according to an embodiment of the present invention;

[0037] Figure 3 is a schematic diagram of the arrangement of the drilling and internal receiving probes of an embodiment of the present invention;

[0038] Figure 4 This is a diagram of the internal structure of a magnetic receiving probe according to an embodiment of the present invention;

[0039] FIG5( a ) is a schematic diagram of the structure of the receiving and sending rod barrel according to an embodiment of the present invention;

[0040] FIG5( b ) is a schematic diagram of the protective sleeve structure of an embodiment of the present invention.

[0041] In the figure: 1 processor, 2 control system, 3 transmitting system, 4 energy storage circuit, 5 power amplifier circuit, 6 transmitting circuit, 7 matching capacitor, 8 transmitting coil, 9 receiving probe, 10 first wall-attached probe, 11 first centered probe, 12 second wall-attached probe, 13 third wall-attached probe, 14 second centered probe, 15 fourth wall-attached probe, 16 receiving system, 17 isolation circuit, 18 preamplifier circuit, 19 filter amplifier circuit, 20 acquisition circuit, 21 power supply, 22 face, 23 shell, 24 skeleton, 25 magnet, 26 antenna, 27 protective sleeve, 28 receiving and sending rod barrel, 29 groundwater source, 30 cable, 31 convex body, 32 groove, 33 probe fixing device, 34 coil bracket, 35 data input module, 36 preprocessing module, 37 inversion processing module, 38 image output module. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0043] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0045] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

[0046] In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meanings of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0047] like Figure 1As shown, a downhole borehole nuclear magnetic resonance detection device of this embodiment includes a transmitting system 3, a transmitting coil 8, a receiving system 16, a receiving probe 9, a control system 2 and a processor 1;

[0048] The control system 2 is connected to the transmitting system 3 and the receiving system 16 respectively;

[0049] The transmitting system 3 is connected to a transmitting coil 8, which is arranged on the tunnel face 22 and is used to transmit a pulse signal of a set frequency and amplitude;

[0050] The receiving system 16 is connected to a receiving probe 9, and the receiving probe 9 is arranged in a borehole of the tunnel face 22, and is used to collect the echo signal of the pulse signal and transmit it to the processor through the receiving system;

[0051] The processor 1 is connected to the control system 2 and is used to obtain detection result data according to the echo signal and analyze the image to identify the groundwater source 29.

[0052] In a specific implementation, the processor 1 includes a data input module 35, a preprocessing module 36, an inversion processing module 37 and an image output module 38 which are connected in sequence. The processor 1 can convert data into a two-dimensional or three-dimensional image.

[0053] It should be noted that the process of obtaining detection result data according to the echo signal and analyzing the imaging can be implemented by using existing algorithms, which will not be described again here.

[0054] The control system 2 is connected to the transmitting system 3, the receiving system 16 and the processor 1 respectively through the cable 30, and can directly send instructions to the transmitting system 3 and the receiving system 16 and control the start or pause of work. After the detection is completed, the acquisition system 16 sends the collected and processed signal data to the processor 1 through the control system 2. In a specific implementation, the borehole is separated from the outer edge of the transmitting coil by a first set distance, and adjacent boreholes are separated by a second set distance. For example: the adjacent boreholes are separated by 3.5 meters, and the borehole is separated from the outer edge of the transmitting coil by 4 meters.

[0055] It should be noted that those skilled in the art may also specifically set the interval between the borehole and the outer edge of the transmitting coil, as well as the interval between adjacent boreholes according to actual conditions.

[0056] The transmitting system 3 is connected to the transmitting coil 8 and can transmit pulses to the transmitting coil 8. The transmitting system 3 comprises a tank circuit 3, a power amplifier circuit 5 and a transmitting circuit 6 which are connected in sequence. The moiré frequency of the transmitting circuit 6 when transmitting the maximum transmitting current matches the capacitance value of the tuning capacitor 7.

[0057] Specifically, the transmitting coil 8 is in a square shape and is placed on a coil support 34 , which is fixed on the tunnel face 22 .

[0058] In a specific implementation, the receiving system 16 is connected to the receiving probe 9 and can receive and amplify the echo signal collected by the receiving probe. The receiving system 16 includes an isolation circuit 17, a preamplifier circuit 18, a filter amplifier circuit 19 and an acquisition circuit 20 connected in sequence, and the input end of the isolation circuit 17 is connected to the receiving probe 9.

[0059] Among them, the isolation circuit 17 can control the contact and isolation between the receiving probe 9 and the receiving system 13, and has the function of protecting the circuit. The preamplifier 18 and the filter amplifier 19 are used. The two amplifiers have the function of amplifying the original echo signal collected by the probe, and the filter amplifier 19 can filter out the noise interference of the echo signal. The acquisition circuit 20 can collect and process the echo signal after amplification and noise filtering.

[0060] As a preferred embodiment, the receiving probe is a permanent magnetic probe. As shown in Figure 2(a) and Figure 2(b), two types of probes are included: wall-attached type and center-centered type. Both probes include a receiving probe housing 23, a receiving probe skeleton 24, a receiving probe magnet 25, and a receiving probe antenna. Figure 2 (a) is a schematic diagram of the structure of a center-centered receiving probe, in which the skeleton is in the center of the probe, and the magnet and antenna are arranged outside the skeleton. Its detection area is the area where the probe is symmetrical with respect to the central axis of the probe. Figure 2(b) is a wall-attached probe, in which the magnet and antenna are respectively located on the left and right sides of the probe, and its detection area is mainly the tile-shaped shell area on the side of the magnet against the wall. The outer shell and skeleton parts are made of high temperature and high pressure resistant materials.

[0061] Specifically, the receiving probe includes a wall-attached probe and a centered probe, both of which include a magnet 25, an antenna 26, a shell 23 and a skeleton 24, wherein the magnet 25, the antenna 26 and the skeleton 24 are all arranged inside the shell 23; the skeleton in the centered probe is in the center of the probe, and the magnet and the antenna are arranged outside the skeleton; the magnet and the antenna of the wall-attached probe are respectively located on the left and right sides of the probe.

[0062] In a specific implementation, the receiving probe is also connected to a probe transmission system, and the probe transmission system is used to carry the receiving probe and receive and transmit the receiving probe in the borehole.

[0063] like Figure 3It is a schematic side view of the overall structure of a downhole nuclear magnetic resonance detection device. Advance drilling is performed on the face 22, and a receiving probe 9 is sent into the borehole through a probe carrying system. The probe transmission system includes a protective sleeve 27, a receiving and sending rod barrel 28, a cable 30, and a probe fixing device 33. The receiving probe is connected to the receiving system 16 through a cable 30. The cable 30 is arranged inside the receiving and sending rod barrel 28. The receiving and sending rod barrel 28 is an insulating sleeve, which can reduce the friction between the cable 30 and the external structure and reduce the cable loss. The protective sleeve 27 is a high-temperature resistant and strong insulating sleeve, which protects the receiving and sending rod barrel 28 and the receiving probe 9. The width of the receiving and sending rod barrel 28 is slightly smaller than the safety sleeve 27, and there is a certain gap between it and the safety sleeve 27. The probe fixing device 33 fixes the receiving probe 9 on the protective rod barrel 28. The processor 1, the control system 2, the transmitting system 3, the transmitting coil 8 and the receiving system 16 are arranged according to Figure 1 The connection method of the device working system block diagram is connected in sequence.

[0064] like Figure 4 Schematic diagram of the arrangement of the transmitting coil, borehole and internal receiving probe. The device adopts a detection method of a transmitting coil and an array receiving probe to achieve one-shot multi-receive. The transmitting coil 8 is arranged on a coil bracket 34 fixed to the face 22. The array receiving probe includes a first intermediate probe 11, a second intermediate probe 14, a first wall-attached probe 10, a second wall-attached probe 12, a third wall-attached probe 13, and a fourth wall-attached probe 15. The first intermediate probe 11, the first wall-attached probe 10, and the second wall-attached probe 12 are arranged in a row, and the second intermediate probe 14, the third wall-attached probe 13, and the fourth wall-attached probe 15 are arranged in a row. The intermediate probe is arranged in the middle of the two wall-attached probes. Two rows of probes are fixed in the corresponding boreholes, and the three probes in each row are connected respectively by cables 30. In this way, signals at multiple locations can be obtained with only one transmission.

[0065] As shown in Fig. 5(a) and Fig. 5(b), convex bodies 31 are provided on both sides of the outer wall of the receiving and sending rod barrel 28. The left and right inner walls of the protective sleeve 27 are designed with grooves 32 corresponding to the receiving and sending rod barrel. The length of the convex body 31 and the groove 32 is two-thirds of the length of the protective sleeve. The two constitute a fixed depth and directional positioning device, which not only specifies the position of the probe in the borehole, but also specifies the direction for the receiving and sending of the protective sleeve in the borehole, avoiding the possibility of collision of the receiving and sending sleeve in the borehole, and at the same time reserving a certain safety distance for the receiving probe. The probe fixing device 33 fixes the receiving probe 9 on the protective rod barrel 28.

[0066] The working method of the downhole borehole nuclear magnetic resonance detection device of this embodiment includes:

[0067] Step 1: According to the size and shape of the tunnel face, advance drilling is performed on the tunnel face and transmitting coils are arranged.

[0068] For example, according to the principle that the interval between adjacent boreholes is 3.5 meters, and the interval between the borehole and the outer edge of the transmitting coil is 4 meters, the installation position of the transmitting coil and the advance drilling position are roughly determined, the advance drilling is carried out on the face, and the protective sleeve is installed in the borehole.

[0069] Step 2: Connect the downhole borehole NMR detection device as described above.

[0070] Specifically, the transmitting coil is laid on the coil bracket and connected to the transmitting system through a cable. The receiving probe is fixed on the top of the receiving and transmitting rod barrel, and the cable connected to the receiving probe is passed through the receiving and transmitting rod barrel and connected to the receiving system. The convex body of the transmission sleeve is aligned with the groove of the protective sleeve, and the receiving probe is sent into the borehole. The center-type receiving probe is placed in the middle borehole, and the boreholes where the two wall-type receiving probes are located are on both sides of the middle borehole. The control system is connected to the processor, the transmitting system, and the receiving system respectively. The power supply is connected to the transmitting system.

[0071] Step 3: Adjust the moiré frequency so that the moiré frequency at the maximum transmitting current matches the capacitance value of the tuning capacitor.

[0072] Specifically, the average value of the geomagnetic field measured multiple times by the geomagnetic field measuring instrument is used as the static magnetic field, and the static magnetic field is multiplied by the magnetic gyrometry ratio of the hydrogen nuclear magnetism to calculate the moiré frequency f. The coil inductance L is measured with an ammeter, and according to the formula (2fπ) 2 L / 1 calculates the tuning capacitance. Adjust the moiré frequency so that the moiré frequency at the maximum transmitting current matches the set capacitance.

[0073] Step 4: The control system sends a signal to the transmitting system, and the transmitting system starts to transmit pulses through the transmitting coil. After the transmission stops and the energy is discharged, the control system sends a collection signal to the receiving system. The receiving system transmits the collected echo signal to the processor to obtain the detection result data and analyze and image it, finally completing the identification of the groundwater source.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A downhole borehole nuclear magnetic resonance detection device, characterized in that: It includes a transmitting system, a transmitting coil, a receiving system, a receiving probe, a control system and a processor; The control system is connected to the transmitting system and the receiving system respectively; The transmitting system is connected to a transmitting coil, which is arranged on the face of the tunnel and is used to transmit a pulse signal of a set frequency and amplitude; The receiving system is connected to a receiving probe, which is arranged in a borehole of the tunnel face and is used to collect the echo signal of the pulse signal and transmit it to the processor via the receiving system; The processor is used to obtain detection result data according to the echo signal and analyze the image to identify the underground water source; The borehole is spaced apart from the outer edge of the transmitting coil by a first set distance, and adjacent boreholes are spaced apart by a second set distance; The transmitting system comprises a tank circuit, a power amplifier circuit and a transmitting circuit which are connected in sequence, and the moiré frequency when the transmitting circuit transmits the maximum transmitting current matches the capacitance value of the tuning capacitor; or / and The receiving system comprises an isolation circuit, a preamplifier circuit, a filter amplifier circuit and an acquisition circuit which are connected in sequence, and the input end of the isolation circuit is connected to the receiving probe; The shape of the transmitting coil is square; The transmitting coil is laid on a coil support, and the coil support is fixed on the tunnel face; The receiving probe is a permanent magnetic probe; The receiving probe includes a wall-attached probe and a center-centered probe, both of which include a magnet, an antenna, a shell and a frame, wherein the magnet, the antenna and the frame are arranged inside the shell; the frame of the center-centered probe is in the center of the probe, and the magnet and the antenna are arranged outside the frame; the magnet and the antenna of the wall-attached probe are respectively located on the left and right sides of the probe; The receiving probe is also connected to a probe transmission system, and the probe transmission system is used to carry the receiving probe and receive and transmit the receiving probe in the borehole; The probe transmission system includes a protective sleeve, a receiving and sending rod barrel, a cable and a probe fixing device. The receiving probe is connected to the receiving system through a cable, and the cable is arranged inside the receiving and sending rod barrel. Protrusions are arranged on both sides of the outer wall of the receiving and sending rod barrel. The protective sleeve is sleeved on the outside of the receiving and sending rod barrel, and the inner wall of the protective sleeve is provided with grooves corresponding to the protrusions. The probe fixing device is arranged on the upper part of the protective sleeve.

2. A method for operating the downhole borehole nuclear magnetic resonance detection device according to claim 1, characterized in that: include: According to the size and shape of the tunnel face, advance drilling and deployment of transmitting coils are carried out on the tunnel face; Connected to the downhole borehole nuclear magnetic resonance detection device as claimed in claim 1; Adjust the moiré frequency so that the moiré frequency at the maximum transmitting current matches the capacitance value of the tuning capacitor; The control system sends a signal to the transmitting system, and the transmitting system starts to transmit pulses through the transmitting coil. After the transmission stops and the energy discharge is completed, the control system sends a collection signal to the receiving system. The receiving system transmits the collected echo signal to the processor to obtain the detection result data and analyze and image it, finally completing the identification of the groundwater source.

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