Method for increasing penetration of sound waves in soft coal seams

Abstract

The application discloses a soft coal seam acoustic wave penetration method, comprising the following steps: sampling the rock of one side rock stratum of the soft coal seam to be penetrated, obtaining the tensile strength and shear strength of the rock, the one side rock stratum being the coal seam roof or the coal seam floor; drilling a working borehole in the one side rock stratum; implementing impact in the working borehole; the impact wave generated by the impact cracks the rock stratum around the working borehole, the impact wave cracks the rock stratum, and the acoustic wave is formed after the impact wave attenuates, the acoustic wave is used for penetrating the soft coal seam, wherein the stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock. The application solves the problems that it is difficult to develop an effective high-strength sound source capable of being loaded to the coal seam and it is difficult to implement drilling in the soft coal seam in the prior art. The application converts the strong impact into high-strength acoustic wave by using the coal seam roof or the coal seam floor rock stratum, the high-strength acoustic wave is used for penetrating and exciting the coal seam, and the required acoustic wave can be obtained, and the gas desorption is promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal seam permeability improvement, and particularly relates to a soft coal seam acoustic permeability improvement method. BACKGROUND

[0002] China's primary consumption energy mainly relies on coal supply, and the proportion has been more than 60% for a long time, which is the main pillar of China's industrial development. China's coal production has reached a high level of 4 billion tons per year, and about one-third of the national coal production, about 1 billion tons, is produced from high gas mines, high gas outburst mines and high gas emission mines. The gas safety problem in coal production is very serious, and the loss caused by gas control problem is also very serious.

[0003] In order to solve the gas problem in coal production, the most effective gas control measure at present is intensive drilling and long-term pre-drainage, including bedding drilling and through drilling. The new coal seam permeability improvement technology based on controllable shock wave technology has been applied in many coal mines, which has been proved to be very effective and has been widely used in the coal industry. However, various active disturbance type coal seam strengthening measures, while strengthening and permeability improving the coal seam, also harm the coal seam, which reduces the gas analysis capacity of the coal seam. From the perspective of coexistence of permeability improvement and harm, only high-strength acoustic waves have the smallest harm to the coal seam, the largest permeability improvement effect and range, and the effect of promoting gas desorption. However, the main reason why the high-strength acoustic wave strengthening coal seam measure cannot be widely applied is that it is difficult to develop an effective high-strength acoustic source that can be loaded into the coal seam. At the same time, it is difficult to implement drilling in soft coal seams, or the implemented drilling is extremely easy to collapse, so the existing measures cannot meet the demand of gas control. SUMMARY

[0004] The embodiment of the application provides a soft coal seam acoustic permeability improvement method, which solves the problem that an effective high-strength acoustic source that can be loaded into the coal seam is difficult to develop in the prior art. The embodiment of the application breaks through the limitation that the existing permeability improvement measures are only implemented in soft coal seams, and uses an impact source to impact the roof and floor rock strata in the drilling of the roof and floor rock strata of the coal seam. Firstly, the rock strata between the strong impact induced fracture drilling and the coal seam are used as transducers to convert the impact into strong acoustic waves, thereby obtaining an effective high-strength acoustic source.

[0005] In order to achieve the above purpose, the embodiment of the application provides a soft coal seam acoustic permeability improvement method, which comprises the following steps:

[0006] The rock of the rock strata on one side of the soft coal seam to be permeability improved is sampled to obtain the tensile strength and shear strength of the rock, and the rock strata on one side are the roof or floor of the coal seam;

[0007] A working drill hole is drilled in the one side rock stratum; impact is implemented in the working drill hole with a set working intensity, and the rock stratum around the working drill hole is cracked by the shock wave generated by the impact, and the sound wave is formed after the shock wave cracking the rock stratum attenuates, and the sound wave transmits the soft coal seam, wherein the stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock.

[0008] In a possible implementation, the following steps are performed before the working drill hole is drilled in the one side rock stratum:

[0009] A test drill hole is drilled in the one side rock stratum, and impact is implemented in the test drill hole to generate a shock wave, so that the stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock;

[0010] The rock stratum around the test drill hole is cracked by the shock wave, the sound wave is formed after the shock wave cracking the rock stratum attenuates, the maximum sound pressure of the sound wave is measured, the intensity of the shock wave generated by the impact is regulated according to the maximum sound pressure, so that the maximum sound pressure is less than the tensile strength and shear strength of the soft coal seam, and the intensity of the shock wave at this time is the working intensity.

[0011] In a possible implementation, when the maximum sound pressure is measured, the sound intensity and sound pressure of the sound wave at each place in the soft coal seam are calculated, and the effective action distance of the sound wave is determined according to the tensile strength and shear strength of the soft coal seam.

[0012] The position of the working drill hole and the distance between the working drill hole and the soft coal seam are set according to the effective action distance.

[0013] In a possible implementation, the effect of the sound wave transmitting the soft coal seam is observed, and if the effect does not meet the expected setting, the working drill hole is impacted again with the same shock wave intensity for multiple times.

[0014] In a possible implementation, the sound wave entering the soft coal seam propagates in the soft coal seam under the constraint of the coal seam roof and the coal seam floor, and forms a channel wave, and the channel wave converges in the area of the soft coal seam where the channel wave is strengthened, so that the soft coal seam in the area is further transmitted.

[0015] In a possible implementation, the shock wave attenuates to form a low-frequency sound wave.

[0016] The one or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0017] This invention provides a method for enhancing the acoustic permeability of soft coal seams. The method first involves applying a strong impact to the rock strata in the roof or floor of the coal seam. This strong impact first fractures the roof or floor, forming an impact fracture zone that connects the borehole and the coal seam. Simultaneously, the roof or floor attenuates and slows down the impact from the borehole into a high-intensity acoustic wave, which is then loaded onto the coal seam to form an impact desorption zone, further enhancing the permeability and excitation of the coal seam. This invention addresses the difficulty of drilling in soft coal seams by setting the borehole in the roof or floor where drilling is easily possible. The impact wave directly fractures the rock strata between the borehole and the coal seam, connecting them and overcoming the limitation of existing permeability enhancement measures in soft coal seams, which are confined to drilling within the coal seam itself. This invention utilizes the roof or floor rock strata to convert the strong impact into a high-intensity acoustic wave, solving the practical problem of not being able to create an effective strong acoustic wave source. The method of this invention can obtain high-intensity acoustic waves that are directly loaded onto the coal seam. This method does not damage the coal seam, while obtaining the required sound waves to achieve the expected permeability enhancement effect and range, promote gas desorption, and meet the needs of gas control. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the shock wave disturbance zone provided in an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of the crushing zone in a soft coal seam, provided in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of the structure of a coal seam subjected to controllable impact fracturing, as provided in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of a channel wave propagating in a coal seam, provided as an embodiment of the present invention.

[0023] Figure 5 A flowchart of a method for enhancing acoustic permeability in soft coal seams provided in an embodiment of the present invention.

[0024] Figure labels: 1-Shock wave; 2-Compressive stress wave; 3-Elastic acoustic wave; 4-Fracturing zone; 5-Drill hole; 6-Coal seam roof; 7-Coal seam floor. Detailed Implementation

[0025] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0026] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like is the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance. In addition, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0027] As shown in Figures 1 to 5 The soft coal seam acoustic wave penetration method provided by the embodiments of the present application comprises the following steps:

[0028] The rock of one side rock stratum of the soft coal seam to be penetrated is sampled to obtain the tensile strength and shear strength of the rock. The one side rock stratum is the coal seam roof or the coal seam floor.

[0029] A working drill hole is drilled in the one side rock stratum. Impact is carried out in the working drill hole at a set working intensity. The impact wave generated by the impact cracks the rock stratum around the working drill hole. The impact wave that cracks the rock stratum forms an acoustic wave after attenuation. The acoustic wave penetrates the soft coal seam. The stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock. In actual application, the stress wave pressure entering the soft coal seam is slightly lower than the tensile strength and shear strength of the rock, so that a larger intensity acoustic wave can be formed.

[0030] It should be noted that, as shown in Figure 2 The impact wave generated by the impact can form a crushing zone 4, a fracture zone, a radial crack and a hoop crack. The fracture zone, the radial crack and the hoop crack communicate the drill hole with more coal seams. However, the crushing zone 4 consumes a large amount of energy and causes damage to the drill hole 5 and the coal seam, so the impact intensity needs to be controlled to avoid the formation of the crushing zone 4, such asFigure 3 The impact strength is selected to only crack the rock layer between the borehole and the coal seam.

[0031] As shown in the figure, the shock wave 1 can form a shock wave disturbance zone to the coal seam, and when the strength of the shock wave 1 is greater than the strength of the rock layer, the rock layer is cracked in a direct rupture mode. In the region where the strength decays below the compressive strength but is still higher than the tensile strength and shear strength, the rock layer is torn by the compressive stress wave 2, and finally decays into a high-strength elastic sound wave 3 with the rock layer and coal seam material parameters. The cracked rock layer forms a shock fracture zone, and the elastic sound wave 3 forms a shock desorption zone. Figure 1 The present application first applies a strong impact to the rock layer of the coal seam roof or coal seam floor. The strong impact first cracks the coal seam roof or coal seam floor to form a shock fracture zone, which communicates the borehole and the coal seam, and at the same time, the shock in the borehole is attenuated and moderated by the coal seam roof or coal seam floor to form a shock desorption zone by reloading the high-strength sound wave to the coal seam, and the coal seam is further permeabilized and excited. The present application does not first generate a sound field and then load it to the coal seam, but applies an impact to the coal seam roof or coal seam floor region, and converts the impact to a sound wave sound field and then loads it to the coal seam, which can obtain a high-strength sound wave directly loaded to the coal seam.

[0032] The present application aims at the problem of difficult drilling in soft coal seams, and sets the borehole in the rock layer of the coal seam roof or coal seam floor, and the shock wave directly cracks the rock layer between the borehole and the coal seam to communicate the borehole and the coal seam. The borehole drilled in the roof can be drilled from the underground roadway or from the ground. The borehole drilled in the rock layer of the coal seam roof or coal seam floor has the same operation mode as the coal seam drilling, and for several impact sources that can only be used once, the strength must be reduced and used in sections to avoid damaging the coal seam roof or coal seam floor.

[0033] The present application converts a strong impact to a high-strength sound wave by using the rock layer of the coal seam roof or coal seam floor, and by controlling the impact strength, the coal seam damage can be reduced. The present application solves the practical problem that a strong sound wave can effectively tear and permeabilize and excite the coal seam desorption, but cannot manufacture an effective strong sound wave source. Through various impact wave sources, the impact wave strength and the distance between the rock layer borehole and the coal seam are controlled to control the impact wave energy and the degree of cracking the rock layer to protect the coal seam roof. By arranging the boreholes and segmented operation in the boreholes, the overall balanced reinforcement of the working face and the heading roadway can be realized.

[0034]

[0035] ​Because the mechanical strength of rock and coal seam is quite different, even if the stress wave intensity of rock stratum cannot be cracked into coal seam, it can also tear the coal seam. According to the design of the shock wave intensity and the distance between the borehole and the coal seam in the previous section, the stress wave pressure entering the coal seam is just lower than the tensile and shear strength of the rock stratum. Further, the intensity of the shock wave in the rock stratum after doing work and attenuating is just lower than the tensile and shear strength of the rock stratum, which reduces the damage of the shock wave to the roof and floor.

[0036] When the rock stratum is strongly impacted, the shock wave in the rock stratum attenuates and evolves into high-strength acoustic wave, and the vibration of the rock stratum radiates high-strength acoustic wave to the coal seam.

[0037] The main reason for the poor effect of the current various active disturbance type measures is that the damage effect is large and the permeability improvement effect is small. The main reasons are as follows: 1. The permeability improvement measures are implemented in the coal seam, which is not conducive to implementation and increases the damage effect to the coal seam. 2. When the high-strength acoustic wave with the best permeability improvement effect to the coal seam is used, it is always tried to generate high-strength acoustic wave first and then load it to the coal seam. However, according to the principle of acoustic wave generation, it is impossible to generate high-strength acoustic wave first.

[0038] In this embodiment, the following steps are performed before a working borehole is drilled in one side of the rock stratum:

[0039] A test borehole is drilled in one side of the rock stratum, and the impact is implemented in the test borehole to generate a shock wave, so that the stress wave pressure entering the soft coal seam is lower than the tensile and shear strength of the rock.

[0040] The rock stratum around the test borehole is cracked by the shock wave, and the shock wave after cracking the rock stratum forms an acoustic wave. The maximum sound pressure of the acoustic wave is measured, and the intensity of the shock wave generated by the impact is adjusted according to the maximum sound pressure, so that the maximum sound pressure is less than the tensile and shear strength of the soft coal seam. At this time, the intensity of the shock wave is the working intensity.

[0041] It should be noted that setting the maximum sound pressure of the generated acoustic wave to be less than the tensile and shear strength of the soft coal seam can ensure that the strongest acoustic wave is obtained. The intensity of the shock wave can also be controlled to control the intensity of the acoustic wave, and further ensure that the acoustic wave will not damage the coal seam, while achieving the best permeability improvement effect.

[0042] When the maximum sound pressure of the acoustic wave is measured, the intensity and pressure of the acoustic wave at each place in the soft coal seam are calculated, and the effective action distance of the acoustic wave is determined according to the tensile and shear strength of the soft coal seam, so as to ensure the maximum permeability improvement effect without damaging the coal seam.

[0043] In this embodiment, when the maximum sound pressure is measured, the sound intensity and sound pressure of the acoustic wave at each place in the soft coal seam are calculated, and the effective action distance of the acoustic wave is determined according to the tensile and shear strength of the soft coal seam.

[0044] According to the effective action distance, the position of the working drill hole and the distance between the working drill hole and the soft coal seam are set.

[0045] It should be noted that the sound intensity and sound pressure of the high-intensity sound wave in the coal seam are calculated, and according to the anti-expansion and anti-shear strength of the coal seam, the effective distance of the high-intensity sound wave tearing the coal seam can be judged, so as to assist the staff to arrange the position of the working drill hole and the position and spacing of the impact, and then realize the best permeability improvement effect and improve the operation efficiency.

[0046] In this embodiment, the effect of the sound wave in improving the soft coal seam is observed, and if the effect does not meet the expected setting, the working drill hole is impacted again with the same impact wave intensity and multiple times.

[0047] It should be noted that the sound wave action time is positively correlated with the coal seam permeability improvement and the gas desorption capacity, and is negatively correlated with the adsorption capacity. Multiple impacts in the drill hole can increase the sound wave operation time. When the multiple loading mode is adopted, the expansion effect of multiple impacts should also be considered, and specific test research should be conducted on various rock layers and coal seams. According to a large number of test results, the sound wave operation time is positively correlated with the permeability, so increasing the impact times can increase the sound wave action time, and this way can generate more and richer cracks in the coal seam to communicate the drill hole with more coal seams.

[0048] If the sound wave effect under this intensity does not meet the expected setting, that is, the purpose of exciting the coal seam cannot be achieved, the impact times can be increased to increase the sound wave action time, so as to use the fatigue effect to improve the permeability of the coal seam. If the effect still does not meet the expected setting, the impact wave intensity can be appropriately increased for multiple times of impact.

[0049] The present application expands the cracks in the rock layer by means of the fatigue effect of multiple actions, and the distance between the drill hole and the coal seam is designed by controlling the impact times, and about 1 meter is the best. Both the impact wave intensity is saved, and the deep part of the roof and floor is not damaged.

[0050] In this embodiment, the sound wave entering the soft coal seam propagates in the soft coal seam under the constraint of the coal seam roof and the coal seam floor, the propagating sound wave forms a channel wave, and the channel wave realizes further permeability improvement of the soft coal seam in the area where the channel wave is gathered and strengthened in the soft coal seam.

[0051] It should be noted that, as Figure 4As shown, the sound waves generated in the rock stratum, most of the sound wave energy cannot be transmitted to the coal seam roof 6 and the coal seam floor 7, but can only propagate in the coal seam under the constraint of the coal seam roof 6 and the coal seam floor 7, which forms a channel wave, even if the intensity of the channel wave is not enough to excite the coal seam, through the reflection of the coal seam roof 6 and the coal seam floor 7, it can still be strengthened in a certain area of the coal seam due to convergence, and further realize the further penetration of the coal seam in that place, and the propagation mode of the channel wave in the coal seam is shown in Figure 4 .

[0052] Any structure has a natural frequency, and the coal seam roof 6 and the coal seam floor 7 and the faults and pore cracks in the coal seam are large and micro structures, when these structures resonate with external sound waves or self-excited sound waves, better tearing and excitation can be generated, further promoting the effect of gas desorption.

[0053] In this embodiment, the part from the hole opening of the working borehole to 30 meters in the hole is a non-working area.

[0054] It should be noted that at the borehole opening, generally more than 30 meters of non-impact area is reserved to avoid the cracks produced by the strengthening effect connecting the borehole and the roadway.

[0055] In this embodiment, when the impact is implemented in the working borehole, the rock stratum is first fractured by high-energy gas fracturing, deep-hole pre-splitting blasting, carbon dioxide fracturing, or nitrogen foam fracturing, and then the working borehole is impacted multiple times by the controllable shock wave device.

[0056] It should be noted that in order to ensure the effect, the rock stratum between the borehole and the coal seam can be fractured by high-energy gas fracturing, deep-hole pre-splitting blasting, carbon dioxide fracturing, or nitrogen foam fracturing, etc., but the impact is required to be implemented in sections, and the rock stratum in the whole well section is fractured uniformly, and then the working borehole is impacted multiple times by the controllable shock wave device. The process of using the controllable shock wave device to implement the impact is prior art, and the specific steps can refer to the steps of the patent of the method for increasing the permeability of the coal seam in the coal seam roof and floor borehole, CN111456801B, which can meet the purpose of implementing the impact and generating a shock wave of a set intensity in the hard coal seam sound wave permeability increasing method.

[0057] In this embodiment, the shock wave attenuates to form a low-frequency sound wave.

[0058] It should be noted that the attenuation coefficient of sound wave propagation in medium is closely related to the frequency of sound wave, and the absorption attenuation reflects the ability of sound wave in medium, and the scattering attenuation reflects the diffraction trend of sound wave in medium. Therefore, the effect of loading low-frequency sound wave to the coal seam is better, and the effective range is larger.

[0059] In this embodiment, the working drill hole is drilled in the area of the coal seam roof or coal seam floor where the brittle rock is stronger.

[0060] It should be noted that the brittle rock is easy to drill, and it is also easy to be cracked by impact, thereby generating strong sound waves.

[0061] It is apparent for those skilled in the art that the present application is not limited to the details of the above-described exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the above description, and all changes coming within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

1. A method for increasing the penetration of sound waves in soft coal seams, characterized in that, The method comprises the following steps: sampling the rock of one side stratum of the soft coal seam to be increased in permeability, obtaining the tensile strength and shear strength of the rock, the one side stratum being the coal seam roof or coal seam floor; drilling a test borehole in the one side stratum, and implementing impact in the test borehole to generate an impact wave, so that the stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock; the impact wave cracks the rock around the test borehole, and the impact wave after cracking the rock forms an acoustic wave, the maximum sound pressure of the acoustic wave is measured, the strength of the impact wave generated by the impact is regulated according to the maximum sound pressure, so that the maximum sound pressure is lower than the tensile strength and shear strength of the soft coal seam, and the strength of the impact wave at this time is the working strength; when the maximum sound pressure is measured, the sound intensity and sound pressure of the acoustic wave at each place of the soft coal seam are calculated, and the effective action distance of the acoustic wave is determined according to the tensile strength and shear strength of the soft coal seam; the position of a working borehole and the distance between the working borehole and the soft coal seam are set according to the effective action distance; drilling a working borehole in the one side stratum, and implementing impact in the working borehole at the set working strength, the impact wave generated by the impact cracks the rock around the working borehole, the impact wave after cracking the rock forms an acoustic wave, and the acoustic wave increases the permeability of the soft coal seam, wherein the stress wave pressure entering the soft coal seam is lower than the tensile strength and shear strength of the rock.

2. The method of claim 1, wherein: The effect of the acoustic wave increasing the permeability of the soft coal seam is observed, and if the effect does not meet the expected setting, the working borehole is impacted again with the same impact wave strength for multiple times.

3. The method of claim 1, wherein: The acoustic wave entering the soft coal seam propagates in the soft coal seam under the constraint of the coal seam roof and the coal seam floor, the propagating acoustic wave forms a channel wave, and the channel wave realizes further increase in the permeability of the soft coal seam in the area where the channel wave converges and strengthens.

4. The soft seam acoustic wave penetration method of claim 1, wherein: The impact wave after attenuation forms a low-frequency acoustic wave.

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