A nuclear magnetic resonance-based coal reservoir structure testing while-drilling probe and testing method

Abstract

The present invention discloses a nuclear magnetic resonance-based coal reservoir structure testing while-drilling probe and testing method. During the drilling process, nuclear magnetic resonance detection is performed on the coal body around the borehole in real time through the nuclear magnetic resonance probe. After the drilling construction is completed, a nuclear magnetic resonance detection process is realized, and then the borehole can be used for subsequent gas extraction. This one-time drilling has multiple functions. On the one hand, it reduces the need to drill multiple boreholes additionally. On the other hand, nuclear magnetic resonance detection can be performed during the drilling and drilling withdrawal processes respectively through nuclear magnetic resonance testing means, so as to realize real-time in-situ non-destructive monitoring of coal seams and greatly improve the validity and credibility of data. Finally, a plurality of nuclear magnetic relaxation information obtained during drilling and a plurality of nuclear magnetic relaxation information obtained during drilling withdrawal are respectively formed into a set, and judged by set standards, so as to finally determine whether the pore structure of the coal seam around the borehole has changed due to the borehole pressure relief, and then corresponding measures are taken in time according to the changes to ensure the safety of subsequent coal seam mining.

Description

Technical Field

[0001] The invention relates to the technical field of coal seam detection, in particular to a nuclear magnetic resonance-based coal reservoir structure testing while-drilling probe and a testing method. Background Art

[0002] High-precision testing of coal seam structure is one of the important means to evaluate coal resources and coal seam gas distribution. Affected by the in-situ stress and mining stress, the multi-scale pore and fracture structure and distribution in the coal matrix are in a dynamic change process. After the pressure relief borehole is formed, from the perspective of stress release, it is easy to form three zones of "fracture zone-stress concentration zone-original rock stress zone" around the borehole; from the perspective of pore evolution, the complexity of fracture structure distribution radiates around the borehole distance. At present, the existing basic property detection methods of coal seams mainly include drilling method and geophysical method. Among them, the drilling method mainly drills a large number of boreholes into the coal seam to drill cores, and sends them to the laboratory for various basic parameter determinations. This method has a relatively direct and simple testing method, a large amount of core drilling, and relatively sufficient test data. The geophysical method mainly uses a large number of geological exploration instruments (such as electromagnetic radiation instruments, ultrasonic instruments, etc.) to measure a series of parameters of the target coal seam. It requires the deployment of a large number of sensors and the selection of multiple test locations. The data is calculated through the optimization algorithm, and then the basic parameter values ​​related to the coal seam structure are inverted.

[0003] However, the above-mentioned existing technologies still have some limitations in application. For example, the drilling method requires a large amount of core data, which makes it difficult to monitor the in-situ coal body structure. In addition, the results of laboratory testing of the cores obtained do not take into account the influence of the original coal body's geostress, resulting in data distortion. At the same time, the coal rock samples of various laboratory testing methods have strict size requirements and cannot fully reflect the structural distribution of regional coal seams. Geophysical testing instruments are easily affected by natural conditions such as stratum structure, geomagnetic distribution, water and gas storage, resulting in instrument failure, inability to calibrate, data distortion, etc., which can easily cause large errors between test data and real data.

[0004] At present, the use of non-destructive monitoring methods (such as nuclear magnetic resonance) to test coal structure has certain advancement and feasibility. Nuclear magnetic resonance technology is mainly based on 1H protons are used as probes, and the CPMG sequence is used to integrate and invert the attenuation signal of the hydrogen proton spin echo train to obtain the transverse relaxation distribution curve of the sample. However, the current nuclear magnetic resonance method is limited to the test of a single coal rock sample in the saturated and centrifugal state inside the laboratory. The spatial volume proportion of the free pores of the coal rock sample is determined by examining the amplitude difference between the two states, and the real-time impact of the on-site ground stress on the coal body structure is not taken into account. Therefore, how to realize the real-time detection of the reservoir structure inside the coal seam by the nuclear magnetic resonance monitoring technology, and then effectively improve the utilization efficiency of nuclear magnetic resonance and the detection accuracy of the coal seam structure, is one of the research directions of this industry. Summary of the invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides a coal reservoir structure testing downhole probe and testing method based on nuclear magnetic resonance, which can perform real-time nuclear magnetic resonance monitoring of the pore structure of the coal body around the borehole during the borehole pressure relief process, thereby effectively improving the nuclear magnetic utilization efficiency and the detection accuracy of the coal seam structure, and ultimately determining the pore structure of the coal seam around the borehole and its changes.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a nuclear magnetic resonance-based coal reservoir structure testing drilling probe, including a drill bit, a drill rod, a nuclear magnetic resonance probe, an electromagnetic converter, a radio frequency generator and a signal processor, the nuclear magnetic resonance probe including a probe housing, an antenna, an annular main magnet and an annular secondary magnet, there are two annular main magnets, the two annular main magnets are coaxially arranged in the probe housing, and the magnetic conductivity directions of the two annular main magnets are along the directions of their respective axes, there are multiple annular secondary magnets, the multiple annular secondary magnets are equidistantly arranged between the two annular main magnets, and the multiple annular secondary magnets are on the same axis as the two annular main magnets; the magnetic conductivity directions of the multiple annular secondary magnets are all along their respective radial directions; a three-dimensional magnetic line distribution with a spherical structure can be formed between the annular main magnet and the annular secondary magnet; the antenna is integrally wound on the outer circumference of the multiple annular secondary magnets, and the two lead wires of the antenna pass through the probe housing respectively, the inner core of the antenna is a conductive material, and the outer surface is an insulating material; the probe housing is filled with magnetic conductive material, so that the magnetic conductive material is in tight contact with the antenna, the annular main magnet and the annular secondary magnet;

[0007] The probe housing is cylindrical, and bearings are provided at both ends of the probe housing. One end of the drill rod passes through the probe housing and is fixedly connected to the bearing through a support rod, so that the drill rod can rotate relative to the nuclear magnetic resonance probe. The drill bit is fixed at one end of the drill rod, and the electromagnetic converter is connected to two lead wires. The radio frequency generator and the signal processor are respectively connected to the electromagnetic converter through a signal transmission line.

[0008] Furthermore, the S poles of the two annular main magnets are arranged opposite to each other; the inner circumferential surface of the annular secondary magnet is the S pole, and the outer circumferential surface is the N pole.

[0009] Furthermore, it also includes a circular wire fixer, which includes an annular disc and a plurality of telescopic springs. The annular disc is sleeved on the drill rod, and one end of the plurality of telescopic springs is respectively connected to the inner circumferential surface of the annular disc, and the other ends are connected to each other; the annular disc has two threading holes, so that the two lead wires of the antenna pass through the annular disc from the two threading holes respectively, and the side of the lead wire is fixedly connected to the threading holes; the annular disc is made of elastic material. Setting this structure can play a guiding and limiting role for the two lead wires, preventing the lead wires from contacting and rubbing with the borehole wall during drilling, causing damage; in addition, since the telescopic spring and the annular disc are made of elastic material and have telescopic function, they can be adjusted accordingly with the change of the borehole diameter during drilling.

[0010] A method for testing a drilling probe for coal reservoir structure testing based on nuclear magnetic resonance, the specific steps are:

[0011] A. First determine the drilling location in the air intake or return air channel, then install a water drill rig at that location, install the drilling probe on the water drill rig, and arrange the electromagnetic converter, radio frequency generator and signal processor in the air intake or return air channel, and connect them to each other at the same time;

[0012] B. Before starting the drilling construction, the drilling probe is first demagnetized. After completion, the drilling rig is used to drive the drilling probe to advance the coal seam. During the rotation of the drill bit and the drill rod, the nuclear magnetic probe does not rotate with the drilling due to the bearing, thereby ensuring the stability of the subsequent work of the nuclear magnetic probe. During the drilling process, multiple drilling measurement depths are set. Whenever the drilling probe drills to a set drilling measurement depth, the drilling is stopped and the radio frequency generator is turned on. At this time, the radio frequency generator transmits the signal to the antenna after passing through the electromagnetic converter, and transmits the signal from the drilling position to the surrounding through the antenna. The coal seam emits radio frequency pulses. After the medium within the three-dimensional magnetic line distribution range receives the radio frequency pulses, the frequency of the radio frequency pulses is the same as the proton precession frequency of the medium. Therefore, the energy of the radio frequency pulses will be transferred to the protons at a low energy level. After obtaining energy, the protons at a low energy level will transition to a high energy level. Then the radio frequency pulse generator is turned off, and the spin echo train attenuation signal is received in real time through the antenna. The signal is fed back to the signal processor through the electromagnetic converter to obtain the nuclear magnetic relaxation information of the current position. This is repeated to obtain the nuclear magnetic relaxation information of each set drilling measurement depth position during the drilling process.

[0013] C. After the coal seam drilling is completed, the drill is withdrawn. Whenever the drilling probe reaches a set drilling measurement depth, the drill withdrawal work is stopped and the above-mentioned detection process during drilling is repeated, so that the nuclear magnetic relaxation information of each set drilling measurement depth position can be obtained during the drill withdrawal process;

[0014] D. Statistically summarize the nuclear magnetic relaxation information of the same borehole during drilling and drilling back. Set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling to M, and set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling back to N. By comparing the affiliation of these two sets, the pore structure evolution characteristics of the borehole are determined, specifically:

[0015] If M∩N≠M∪N, it is determined that the pore structure of the coal seam around the borehole has changed due to pressure relief; if M∩N=M∪N, it is determined that the pore structure of the coal seam around the borehole has not changed.

[0016] Furthermore, the diameter of the drill hole is 200-250 mm.

[0017] Compared with the prior art, the present invention uses a nuclear magnetic field probe to conduct nuclear magnetic field detection of the coal body around the borehole in real time during the drilling process. After the drilling construction is completed, a nuclear magnetic detection process is realized, and then the borehole can be used for subsequent gas extraction. This one-time drilling has multiple functions. On the one hand, it reduces the need to drill multiple boreholes to obtain a large number of cores, saving a lot of initial cost investment, and realizing multiple uses of one hole; on the other hand, nuclear magnetic detection can be performed during the drilling and drilling withdrawal process by nuclear magnetic testing means, so as to obtain the pore structure evolution and fluid distribution during the entire drilling construction process, realize real-time in-situ non-destructive monitoring of coal seams, and greatly improve the data validity and credibility. Finally, the multiple nuclear magnetic relaxation information obtained during drilling and the multiple nuclear magnetic relaxation information obtained during drilling withdrawal are formed into a set, and the judgment is made by the set standard, and finally it can be determined whether the pore structure of the coal seam around the borehole has changed due to the unloading of the borehole, and then corresponding measures are taken in time according to the changes to ensure the safety of subsequent coal seam mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a location layout diagram of the drilling test of the present invention;

[0019] Figure 2 It is a schematic diagram of the structure of the drilling probe in the present invention;

[0020] Figure 3 It is a cross-sectional schematic diagram of the probe housing, bearing and drill rod in the present invention;

[0021] Figure 4 It is a structural schematic diagram of the annular main magnet in the present invention;

[0022] Figure 5 It is a schematic structural diagram of the annular secondary magnet in the present invention;

[0023] Figure 6 It is a schematic diagram of the magnetic field distribution of the annular main magnet and the annular secondary magnet in the present invention;

[0024] Figure 7 It is a schematic structural diagram of the circular wire fixer in the present invention;

[0025] Figure 8 It is a structural schematic diagram of the antenna in the present invention.

[0026] In the figure: 1-coal seam; 2-air inlet tunnel; 3-drill hole; 4-drill bit; 5-drill rod; 6-probe housing; 7-annular main magnet; 8-annular secondary magnet; 9-antenna; 10-lead wire; 11-circular wire holder; 11-1-annular disk; 11-2-threading hole; 11-3-telescopic spring; 12-electromagnetic converter; 13-signal processor; 14-bearing; 15-support rod; 16-RF generator. DETAILED DESCRIPTION

[0027] The present invention will be further described below.

[0028] like Figure 2 and 3 As shown, a nuclear magnetic resonance-based coal reservoir structure testing downhole probe comprises a drill bit 4, a drill rod 5, a nuclear magnetic resonance probe, an electromagnetic converter 12, a radio frequency generator and a signal processor 13. The nuclear magnetic resonance probe comprises a probe housing 6, an antenna 9, an annular main magnet 7 and an annular secondary magnet 8. There are two annular main magnets 7, which are coaxially arranged in the probe housing 6, and the magnetic conduction directions of the two annular main magnets 7 are along the directions of their respective axes. There are multiple annular secondary magnets 8, which are equidistantly arranged between the two annular main magnets 7, and the multiple annular secondary magnets 8 are on the same axis as the two annular main magnets 7; the magnetic conduction directions of the multiple annular secondary magnets 8 are all along their respective radial directions; as shown in FIG. Figure 4 As shown, the S poles of the two annular main magnets 7 are arranged opposite to each other; Figure 5 As shown, the inner circumference of the annular secondary magnet 8 is an S pole and the outer circumference is an N pole. Figure 6 As shown, a three-dimensional magnetic line distribution in a spherical structure can be formed between the annular main magnet 7 and the annular secondary magnet 8; the antenna 9 is integrally wound on the outer circumference of the plurality of annular secondary magnets 8, and two lead wires 10 of the antenna 9 respectively pass through the probe housing 6, the inner core of the antenna 9 is a conductive material, and the outer surface is an insulating material; the probe housing 6 is filled with a magnetic conductive material, so that the magnetic conductive material is in tight contact with the antenna 9, the annular main magnet 7 and the annular secondary magnet 8; as shown Figure 8 As shown, the antenna 9 is a spiral structure as a whole;

[0029] The probe housing 6 is cylindrical, and bearings 14 are provided at both ends of the probe housing 6. One end of the drill rod 5 passes through the probe housing 6 and is fixedly connected to the bearing 14 through a support rod 15, so that the drill rod 5 can rotate relative to the nuclear magnetic probe. The drill bit 4 is fixed to one end of the drill rod 5. The electromagnetic converter 12 is connected to the two lead wires 10, and the radio frequency generator 16 and the signal processor 13 are respectively connected to the electromagnetic converter 12 through a signal transmission line; Figure 7 As shown, it also includes a circular wire fixer 11, which includes an annular disk 11-1 and a plurality of telescopic springs 11-3. The annular disk 11-1 is sleeved on the drill rod 5, and one end of the plurality of telescopic springs 11-3 is respectively connected to the inner circumference of the annular disk 11-1, and the other ends are connected to each other; the annular disk 11-1 is provided with two threading holes 11-2, so that the two lead wires 10 of the antenna 9 pass through the annular disk 11-1 from the two threading holes 11-2 respectively, and the side of the lead wire 10 is fixedly connected to the threading holes 11-2; the annular disk 11-1 is made of elastic material. Setting this structure can play a guiding and limiting role for the two lead wires 10, preventing the lead wires 10 from contacting and rubbing with the borehole wall during drilling, causing damage; in addition, since the telescopic springs 11-3 and the annular disk 11-1 are made of elastic material and have telescopic function, they can be adjusted accordingly with the change of the borehole diameter during drilling.

[0030] The drill bit 4, drill rod 5, annular main magnet 7, annular secondary magnet 8, electromagnetic converter 12, radio frequency generator 16 and signal processor 13 are all existing components or devices.

[0031] like Figure 1 As shown, the above-mentioned testing method of the drilling probe comprises the following specific steps:

[0032] A. First, determine the construction position of the borehole 3 in the air inlet tunnel 2 or the return air tunnel, then install a water drill rig at the position, install the drilling probe on the water drill rig, and arrange the electromagnetic converter 12, the radio frequency generator 16 and the signal processor 13 in the air inlet tunnel 2 or the return air tunnel, and connect them to each other at the same time;

[0033] B. Before starting the drilling construction, the drilling probe is first demagnetized to eliminate the error affecting the uniformity of the magnetic field. After completion, the drilling rig is used to drive the drilling probe to advance the coal seam. The diameter of the borehole is 200-250 mm. During the rotation of the drill bit 4 and the drill rod 5, the nuclear magnetic probe does not rotate with the drilling due to the action of the bearing 14, thereby ensuring the stability of the subsequent work of the nuclear magnetic probe. During the drilling process 3, multiple drilling measurement depths are set. Whenever the drilling probe drills to a set drilling measurement depth, the drilling is stopped and the radio frequency generator 16 is turned on. At this time, the radio frequency generator 16 transmits the signal to the antenna 9 after passing through the electromagnetic converter 12, and transmits radio frequency pulses from the drilling position to the surrounding coal seams through the antenna 9. The medium within the three-dimensional magnetic line distribution range is After receiving the radio frequency pulse, since the frequency of the radio frequency pulse is the same as the proton precession frequency of the medium, the energy of the radio frequency pulse will be transferred to the protons at the low energy level. After the protons at the low energy level obtain energy, they will transition to the high energy level. Then the radio frequency generating device 16 is turned off. At this time, under the action of the magnetic field, the transverse magnetization vector of the coal medium within the three-dimensional magnetic line distribution range gradually decreases to zero until it disappears, and the longitudinal magnetization vector gradually increases from zero until it recovers to the maximum value (i.e., the equilibrium state). This process is called nuclear magnetic relaxation. During this period, the spin echo train attenuation signal is received in real time by the antenna, and fed back to the signal processor 13 through the electromagnetic converter 12 to obtain the nuclear magnetic relaxation information of the current position; this is repeated, and the nuclear magnetic relaxation information of each set drilling measurement depth position can be obtained during the drilling process;

[0034] C. After the coal seam drilling is completed, the drill is withdrawn. Whenever the drilling probe reaches a set drilling measurement depth, the drill withdrawal work is stopped and the above-mentioned detection process during drilling is repeated, so that the nuclear magnetic relaxation information of each set drilling measurement depth position can be obtained during the drill withdrawal process;

[0035] D. Statistically summarize the nuclear magnetic relaxation information of the same borehole during drilling and drilling back. Set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling to M, and set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling back to N. By comparing the affiliation of these two sets, the pore structure evolution characteristics of the borehole are determined, specifically:

[0036] If M∩N≠M∪N, it is determined that the pore structure of the coal seam around the borehole has changed due to pressure relief; if M∩N=M∪N, it is determined that the pore structure of the coal seam around the borehole has not changed.

[0037] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A nuclear magnetic resonance-based coal reservoir structure testing while drilling probe, characterized in that: The invention comprises a drill bit, a drill rod, a nuclear magnetic probe, an electromagnetic converter, a circular wire fixer, a radio frequency generating device and a signal processor. The nuclear magnetic probe comprises a probe housing, an antenna, an annular main magnet and an annular secondary magnet. There are two annular main magnets, which are coaxially arranged in the probe housing, and the magnetic conduction directions of the two annular main magnets are along the directions of their respective axes. There are multiple annular secondary magnets, which are equidistantly arranged between the two annular main magnets, and the multiple annular secondary magnets are on the same axis as the two annular main magnets. The magnetic conduction directions of the multiple annular secondary magnets are all along their respective radial directions; A three-dimensional magnetic line distribution with a spherical structure can be formed between the annular main magnet and the annular secondary magnet; the antenna is wound around the outer circumference of the multiple annular secondary magnets, and the two lead wires of the antenna pass through the probe housing respectively, the inner core of the antenna is a conductive material, and the outer surface is an insulating material; the probe housing is filled with magnetic conductive material, so that the magnetic conductive material is in tight contact with the antenna, the annular main magnet and the annular secondary magnet; the S magnetic poles of the two annular main magnets are arranged oppositely; the inner circumference of the annular secondary magnet is an S magnetic pole, and the outer circumference is an N magnetic pole; The circular wire fixer comprises an annular disc body and a plurality of telescopic springs, the annular disc body is sleeved on the drill rod, one end of the plurality of telescopic springs is respectively connected to the inner circumferential surface of the annular disc body, and the other ends are connected to each other; the annular disc body is provided with two threading holes, so that the two lead wires of the antenna pass through the annular disc body from the two threading holes respectively, and the side of the lead wire is fixedly connected to the threading holes; the annular disc body is made of elastic material; The probe housing is cylindrical, and bearings are provided at both ends of the probe housing. One end of the drill rod passes through the probe housing and is fixedly connected to the bearing through a support rod, so that the drill rod can rotate relative to the nuclear magnetic resonance probe. The drill bit is fixed at one end of the drill rod, and the electromagnetic converter is connected to two lead wires. The radio frequency generator and the signal processor are respectively connected to the electromagnetic converter through a signal transmission line.

2. A method for testing a nuclear magnetic resonance-based while-drilling probe for testing coal reservoir structure according to claim 1, characterized in that: The specific steps are: A. First determine the drilling location in the air intake or return air channel, then install a water drill rig at that location, install the drilling probe on the water drill rig, and arrange the electromagnetic converter, radio frequency generator and signal processor in the air intake or return air channel, and connect them to each other at the same time; B. Before starting the drilling construction, the drilling probe is first demagnetized. After completion, the drilling rig is used to drive the drilling probe to advance the coal seam. During the rotation of the drill bit and the drill rod, the nuclear magnetic probe does not rotate with the drilling due to the bearing, thereby ensuring the stability of the subsequent work of the nuclear magnetic probe. During the drilling process, multiple drilling measurement depths are set. Whenever the drilling probe drills to a set drilling measurement depth, the drilling is stopped and the radio frequency generator is turned on. At this time, the radio frequency generator transmits the signal to the antenna after passing through the electromagnetic converter, and transmits the signal from the drilling position to the surrounding through the antenna. The coal seam emits radio frequency pulses. After the medium within the three-dimensional magnetic line distribution range receives the radio frequency pulses, the frequency of the radio frequency pulses is the same as the proton precession frequency of the medium. Therefore, the energy of the radio frequency pulses will be transferred to the protons at a low energy level. After obtaining energy, the protons at a low energy level will transition to a high energy level. Then the radio frequency pulse generator is turned off, and the spin echo train attenuation signal is received in real time through the antenna. The signal is fed back to the signal processor through the electromagnetic converter to obtain the nuclear magnetic relaxation information of the current position. This is repeated to obtain the nuclear magnetic relaxation information of each set drilling measurement depth position during the drilling process. C. After the coal seam drilling is completed, the drill is withdrawn. Whenever the drilling probe reaches a set drilling measurement depth, the drill withdrawal work is stopped and the above-mentioned detection process during drilling is repeated, so that the nuclear magnetic relaxation information of each set drilling measurement depth position can be obtained during the drill withdrawal process; D. Statistically summarize the nuclear magnetic relaxation information of the same borehole during drilling and drilling back. Set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling to M, and set the set of nuclear magnetic relaxation information of each set drilling measurement depth position obtained during drilling back to N. By comparing the affiliation of these two sets, the pore structure evolution characteristics of the borehole are determined, specifically: like , it is determined that the pore structure of the coal seam around the borehole has changed due to pressure relief; if , it is determined that the pore structure of the coal seam around the borehole has not changed.

3. The method for testing a coal reservoir structure while drilling probe based on nuclear magnetic resonance according to claim 2, characterized in that: The diameter of the drill hole is 200-250 mm.

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