ENHANCED EXTRACTION SYSTEM AND METHOD BASED ON ULTRASONIC EXCITATION AND ACID FRACTURING INTEGRATED PERMEABILITY ENHANCEMENT FOR COAL SEAM

Abstract

The invention discloses an enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam, including an ultrasonic excitation and acid fracturing integrated drilling device, an ultrasonic control box and a mixing tank. The invention further discloses an enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam. The invention has the advantages of realizing intercoupling of ultrasonic excitation and acid fracturing, improving the pore structure of coal, enhancing the connectivity between pores and fractures, promoting gas desorption and improving gas extraction efficiency of coal seams.

Claims

1. An enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam, comprising an ultrasonic excitation and acid fracturing integrated drilling device (a) located in an extraction borehole (2) and an ultrasonic control box (6) and a mixing tank (8) which are located outside the extraction borehole (2), wherein a liquid inlet end of the ultrasonic excitation and acid fracturing integrated drilling device (a) is connected to the mixing tank (8) by means of a fracturing pump (7); the ultrasonic excitation and acid fracturing integrated drilling device (a) comprises a liquid feed rod (a5), an ultrasonic transducer (a1), a fracturing cavity (a2) and a conical drill bit (a4) which are sequentially arranged from left to right and a plurality of openable tool assemblies (a3) located on left and right sides of the fracturing cavity (a2) in mirror symmetry; each said openable tool assembly (a3) comprises a slot (a31), a spool vertical moving rack (231) arranged beside the slot (a31) and capable of moving upwards and downwards, a tool gear (a33) fixed to a lower left corner of the slot (a31) and a tool (a34) fixed to a rotating shaft of the tool gear (a33), the tool gear (a33) is meshed with the spool vertical moving rack (a32), a side, away from the rotating shaft of the tool gear (a33), of the tool (a34) is provided with an arc-shaped edge, a spine of the tool (a34) is matched with an opening of the slot (a31) when the tool (a34) is retracted into the slot (a31), and a reset spring (a35) connected to the edge of the tool (a34) is arranged in a middle of a horizontal surface of an inner side of the slot (a31); when the fracturing cavity (a2) reaches a set pressure, the spool vertical moving rack (a32) moves upwards, and the tool gear (a33) rotates clockwise to drive the tool (a34) to be opened; and when the fracturing cavity (a2) does not reach the set pressure, the tool (a34) is retracted into the slot (a31) under the action of a resilience of the reset spring (a35).

2. The enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 1, wherein the number of the openable tool assemblies (a3) is six, and the number and position of the openable tool assemblies (a3) that are opened are selected according to a hardness coefficient of coal or an area of a target permeability-enhancement region.

3. The enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 1, wherein a high-pressure and corrosion-resistant hose (9) led into the fracturing cavity (a2) is arranged in the liquid feed rod (a5), a liquid inlet of the liquid feed rod (a5), the fracturing pump (7) and the mixing tank (8) are connected by means of the high-pressure and corrosion-resistant hose (9), a control valve (4) is mounted between the fracturing pump (7) and the mixing tank (8), and the ultrasonic control box (6) and the ultrasonic transducer (a1) are connected by means of a cable.

4. An enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam, comprising the following steps: S1, acquiring a sample in a coal seam (1), carrying the sample back into a laboratory, and performing a gas desorption test on the sample with ultrasonic waves at different frequencies to determine an optimal frequency f.sub.1; then, performing proximate analysis, elemental analysis and mineral content analysis on the acquired sample, and obtaining an optimal acid fracturing fluid proportion by theoretical analysis and experimental study; S2, constructing four extraction boreholes (2) in the coal seam (1) at different intervals, disposing the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 1 in one of the extraction boreholes (2), mounting extraction sieve tubes (3) in the other extraction boreholes (2), and connecting the extraction sieve tubes (3) to negative-pressure branches (11) by means of hoses (10); S3, performing gas concentration detection on the extraction boreholes (2) where the extraction sieve tubes (3) are mounted; S4, turning on the ultrasonic control box (6) to adjust an ultrasonic frequency of the ultrasonic transducer (a1) to f.sub.1, turning off the ultrasonic control box (6) 20-30 min later, and then turning on the fracturing pump (7) to inject fracturing liquid in the mixing tank (8) into the extraction borehole (2) to perform fracturing; when a pressure of the fracturing liquid in the extraction borehole (2) is close to a maximum horizontal stress, turning on again the ultrasonic control box (6) to adjust the ultrasonic frequency of the ultrasonic transducer (a1) to f.sub.1, and turning off again the ultrasonic control box (6) 20-30 min later; S5, turning off the fracturing pump (7) after S4 is repeated for five times; then, turning on the ultrasonic control box (6) to adjust the ultrasonic frequency of the ultrasonic transducer (a1) to f.sub.1, and turning off the ultrasonic control box (6) 20-30 min later; and S6, after the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is drawn out, connecting the extraction boreholes (2) to the negative-pressure branches (11) by means of the hoses (10), and performing gas concentration detection on all the extraction boreholes (2).

5. The enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 4, wherein in S1, a theoretical analysis and experimental study process for obtaining the optimal acid fracturing fluid proportion comprises: testing an original permeability of the sample as reference, then selecting an acid solution according to mineral species in coal, then determining mass fractions of acids required according to mineral contents in a test result and a chemical reaction ratio of minerals, and finally, designing a pulverized coal corrosion experiment and a permeability testing experiment according to the mineral contents of the coal and proportions of relative contents of minerals under the precondition that an actual pre-extraction and permeability enhancement time is taken into account, to obtain the optimal acid fracturing fluid proportion.

6. The enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 4, wherein openings of all the extraction boreholes (2), where the extraction sieve tubes (3) are mounted, are sealed with capsules (5).

7. The enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 4, further comprising a step S7: replacing the fracturing liquid in the mixing tank (8) with clear water, turning on the fracturing pump (7), and then cleaning a pump body and the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam.

8. The enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 4, wherein in S2, the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is mounted in the second extraction borehole (2) from left to right, and a distance from the first extraction borehole (2) to the second extraction borehole (2), a distance from the third extraction borehole (2) to the second extraction borehole (2) and a distance from the fourth extraction borehole (2) to the second extraction borehole (2) are respectively 10 m, 20 m and 40 m.

9. The enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam according to claim 4, wherein in S4, in a case where the hardness coefficient of coal is less than 1.5, only two said openable tool assemblies (a3) work; and in a case where targeted permeability enhancement is performed on a specific region, the openable tool assemblies (a3) close to the region work.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0026] FIG. 1 is a schematic installation and use diagram according to the invention.

[0027] FIG. 2 is a schematic structural diagram of an ultrasonic excitation and acid fracturing integrated drilling device.

[0028] FIG. 3 is a schematic structural diagram of an openable tool assembly.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The invention is further described below in conjunction with embodiments and accompanying drawings.

[0030] As shown in FIGS. 1-3, an enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is formed by an ultrasonic excitation and acid fracturing integrated drilling device a located in an extraction borehole 2 and an ultrasonic control box 6 and a mixing tank 8 which are located outside the extraction borehole 2.

[0031] A liquid inlet end of the ultrasonic excitation and acid fracturing integrated drilling device a is connected to the mixing tank 8 by means of a fracturing pump 7.

[0032] The ultrasonic excitation and acid fracturing integrated drilling device a is formed by a liquid feed rod a5, an ultrasonic transducer a1, a fracturing cavity a2 and a conical drill bit a4 which are sequentially arranged from left to right and a plurality of openable tool assemblies a3 which are located on left and right sides of the fracturing cavity a2 in mirror symmetry.

[0033] A high-pressure and corrosion-resistant hose 9 led into the fracturing cavity a2 is arranged in the liquid feed rod a5.

[0034] A liquid inlet of the liquid feed rod a5, the fracturing pump 7 and the mixing tank 8 are connected by means of the high-pressure and corrosion-resistant hose 9.

[0035] A control valve 4 is mounted between the fracturing pump 7 and the mixing tank 8.

[0036] The ultrasonic control box 6 and the ultrasonic transducer a1 are connected by means of a cable.

[0037] Each openable tool assembly a3 is formed by a slot a31, a spool vertical moving rack a32 arranged beside the slot a31 and capable of moving upwards and downwards, a tool gear a33 fixed to a lower left corner of the slot a31 and a tool a34 fixed to a rotating shaft of the tool gear a33.

[0038] The tool gear a33 is meshed with the spool vertical moving rack a32.

[0039] A side, away from the tool gear a33, of the tool a34 is provided with an arc-shaped edge, and when the tool a34 is retracted into the slot a31, a spine of the tool a34 is matched with an opening of the slot a31.

[0040] A reset spring a35 connected to the edge of the tool a34 is arranged in the middle of a horizontal surface of an inner side of the slot a31.

[0041] When the fracturing cavity a2 reaches a set pressure, the spool vertical moving rack a32 moves upwards, and the tool gear a33 rotates clockwise to drive the tool a34 to be opened.

[0042] When the fracturing cavity a2 does not reach the set pressure, the tool a34 is retracted into the slot a31 under the action of a resilience of the reset spring a35.

[0043] The number of the openable tool assemblies a3 is preferably six, and the number and position of the openable tool assemblies a3 that are opened are selected according to a hardness coefficient of coal or an area of a target permeability-enhancement region.

[0044] The conical drill bit a4 is mounted at a right end of the fracturing cavity a2.

[0045] An enhanced extraction method based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam includes the following specific steps:

[0046] S1, a sample in a coal seam 1 is acquired and carried back into a laboratory, and a gas desorption test is performed on the sample with ultrasonic waves at different ultrasonic frequencies to determine an optimal frequency f.sub.1; then, proximate analysis, ultimate analysis and mineral content analysis are performed on the acquired sample, and an optimal acid fracturing liquid proportion is obtained by theoretical analysis and experimental study.

[0047] In S1, a theoretical analysis and experimental study process for obtaining the optimal acid fracturing liquid proportion is as follows: first, the original permeability of the sample is tested as reference, then an acid solution is selected according to mineral species in coal, then mass fractions of acids required are determined according to mineral contents in a test result and a chemical reaction ratio of minerals, and finally, a pulverized coal corrosion experiment and a permeability testing experiment are designed according to the mineral contents of the coal and proportions of relative contents of minerals under the precondition that an actual pre-extraction and permeability enhancement time is taken into account, to obtain the optimal acid fracturing fluid proportion.

[0048] S2, four extraction boreholes 2 are constructed in the coal seam 1, the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is disposed in one of the extraction boreholes 2, the ultrasonic transducer a1 is connected to the ultrasonic control box 6 located outside the extraction boreholes 2 by means of a cable, the fracturing cavity a2 is connected to the mixing tank 8 located outside the extraction boreholes 2 by means of the fracturing pump 7, and extraction sieve tubes 3 are mounted in the other extraction boreholes 2 and connected to negative-pressure branches 11 by means of hoses 10.

[0049] In S2, the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is mounted in the second extraction borehole 2 from left to right, and a distance from the first extraction borehole 2 to the second extraction borehole 2, a distance from the third extraction borehole 2 to the second extraction borehole 2 and a distance from the fourth extraction borehole 2 to the second extraction borehole 2 are respectively 10 m, 20 m and 40 m.

[0050] S3, gas concentration detection is performed on the extraction boreholes 2, where the extraction sieve tubes 3 are mounted, are detected.

[0051] S4, the ultrasonic control box 6 is turned on to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f.sub.1, the ultrasonic control box 6 is turned off 20-30 min later, and then the fracturing pump 7 is turned on to inject fracturing liquid in the mixing tank 8 into the extraction borehole 2 to perform fracturing; when the pressure of the fracturing liquid in the extraction borehole 2 is close to a maximum horizontal stress, the ultrasonic control box 6 is turned on again to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f.sub.1, and the ultrasonic control box 6 is turned off again 20-30 min later.

[0052] In S4, in a case where the hardness coefficient of coal is less than 1.5, only two openable tool assemblies a3 work; and in a case where targeted permeability enhancement is performed on a specific region, the openable tool assemblies a3 close to the region work.

[0053] S5, the fracturing pump 7 is turned off after S4 is repeated for five times; then, the ultrasonic control box 6 is turned on to adjust the ultrasonic frequency of the ultrasonic transducer a1 to f.sub.1, and the ultrasonic control box 6 is turned off 20-30 min later.

[0054] S6, after the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam is drawn out, the extraction boreholes 2 are connected to the negative-pressure branches 11 by means of the hoses 10, and gas concentration detection is performed on all the extraction boreholes 2.

[0055] Openings of all the extraction boreholes 2, where the extraction sieve tubes 3, are mounted are sealed with capsules 5.

[0056] S7, the fracturing liquid in the mixing tank 8 is replaced with clear water, the fracturing pump 7 is turned on, and then a pump body and the enhanced extraction system based on ultrasonic excitation and acid fracturing integrated permeability enhancement for a coal seam are cleaned.