CN113216962A - Synergistic permeability-increasing desorption-promoting experimental system and method for ultrasonic-activated fracturing fluid - Google Patents
Synergistic permeability-increasing desorption-promoting experimental system and method for ultrasonic-activated fracturing fluid Download PDFInfo
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- 230000002195 synergetic effect Effects 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title abstract description 10
- 239000003245 coal Substances 0.000 claims abstract description 226
- 238000002347 injection Methods 0.000 claims abstract description 195
- 239000007924 injection Substances 0.000 claims abstract description 195
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 132
- VTIIJXUACCWYHX-UHFFFAOYSA-L disodium;carboxylatooxy carbonate Chemical compound [Na+].[Na+].[O-]C(=O)OOC([O-])=O VTIIJXUACCWYHX-UHFFFAOYSA-L 0.000 claims abstract description 96
- 229940045872 sodium percarbonate Drugs 0.000 claims abstract description 95
- 239000007788 liquid Substances 0.000 claims abstract description 85
- 238000000605 extraction Methods 0.000 claims abstract description 45
- 238000003795 desorption Methods 0.000 claims abstract description 31
- 238000002474 experimental method Methods 0.000 claims abstract description 22
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- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 45
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Abstract
The invention discloses a synergistic permeability-increasing desorption-promoting experimental system for an ultrasonic activated fracturing fluid, which comprises a plurality of coal seam drill holes arranged in a coal seam, wherein a water injection branch pipe and an ultrasonic transducer are arranged in each coal seam drill hole; a hole packer is arranged at the hole of each coal seam drill hole; a water injection branch pipe in the coal seam drill hole and a connecting circuit of the ultrasonic transducer extend out of the coal seam drill hole; the water injection branch pipe extends out of the coal seam drill hole and is connected with a main liquid injection pipe, the main liquid injection pipe is connected with a liquid injection box, and a sodium percarbonate aqueous solution for promoting coal seam gas desorption under the action of ultrasonic waves is contained in the liquid injection box; the liquid injection main pipe is provided with a liquid injection pump; the connecting line of the ultrasonic transducer is connected with an ultrasonic generator. The invention also discloses a corresponding experimental method. The method promotes the gas desorption of the coal bed while increasing the permeability of the coal bed, greatly improves the volume fraction of the gas to be drained and the daily extraction purity, shortens the fracturing time so as to improve the efficiency, reduces the fracture initiation pressure so as to reduce the energy consumption, and has good popularization and application values.
Description
Technical Field
The invention relates to a coal seam gas extraction technology, which is particularly suitable for low-permeability high-gas coal seams.
Background
Coal bed gas is also called coal bed gas, is a disaster-causing gas causing coal mine gas disasters, and is clean energy which exists in coal beds and is associated with coal. The pre-gas extraction can reduce the gas content and pressure of the coal bed, and reduce or eliminate the risk of coal and gas outburst. However, about 70% of high gas outburst coal seams in China have the characteristics of low porosity, poor permeability and high adsorbability, and meanwhile, as the mining depth of the coal seam increases, the ground stress gradually increases, the permeability of the coal seam continuously decreases, and gas is difficult to desorb in the extraction process, so that the outburst prevention effect of the area adopting the technical measure of gas pre-extraction is poor, and the normal production replacement of a mine is influenced.
In order to improve the gas extraction effect, the desorption and seepage of the gas in the coal bed are accelerated while the gas permeability of the coal bed is improved. The existing coal seam permeability-increasing technology widely applied mainly comprises hydraulic fracturing, high-pressure water jet, microwave excitation and deep-hole CO2Blast presplitting, etc., in practice of actual engineeringThe permeability of the coal seam can be improved to a certain extent by adopting a single coal seam permeability increasing technology, but all the technologies have the use conditions and limitations, the permeability of the coal seam and gas desorption are difficult to consider simultaneously, and the gas extraction and promotion effect is limited.
The ultrasonic wave is used as a novel technology for treating an oil layer, has the advantages of no pollution, low energy consumption, quick response and the like, can cause the fracturing fluid to generate cavitation phenomenon at high temperature and low pressure, and obtains better effect on the aspect of increasing the yield of petroleum by improving the permeability of oil rock mass, reducing viscosity, removing scale, removing blockage and the like.
In the field of permeability increase of low-permeability coal seams, because a single ultrasonic technology is difficult to generate cracks in a large range, the method is usually used in combination with hydraulic fracturing measures.
Because the coal bed hydraulic fracturing is usually carried out at low temperature (15-25 ℃) and high pressure (25-30 MPa) in the actual engineering, in order to fully exert the fracturing and permeability-increasing effect of the ultrasonic cavitation on coal bodies, the temperature of the fracturing liquid needs to be continuously increased, and the engineering energy consumption and difficulty are increased.
Therefore, in order to overcome the defects in the prior art, it is necessary to develop a synergistic permeability-increasing method for enhancing gas extraction by modifying coal in situ by using an ultrasonic-activated fracturing fluid.
Disclosure of Invention
The invention aims to provide a synergistic permeability-increasing desorption-promoting experimental system for ultrasonic-activated fracturing fluid, which promotes the gas desorption of a coal bed while increasing the permeability of the coal bed.
In order to achieve the purpose, the synergistic permeability-increasing desorption-promoting experimental system for the ultrasonic activated fracturing fluid comprises a plurality of coal seam drill holes arranged in a coal seam, wherein a water injection branch pipe and an ultrasonic transducer are arranged in each coal seam drill hole; a hole packer is arranged at the hole of each coal seam drill hole; the water injection branch pipes in the coal seam drill holes and the connecting lines of the ultrasonic transducers penetrate through the corresponding hole packers and extend out of the coal seam drill holes;
the water injection branch pipe extends out of the coal seam drill hole and is connected with a liquid injection main pipe, the liquid injection main pipe is connected with a liquid injection box, sodium percarbonate water solution used for promoting coal seam gas desorption under the action of ultrasonic waves is contained in the liquid injection box, and the mass concentration of the sodium percarbonate is 0.1-10 per mill; the liquid injection main pipe is provided with a liquid injection pump; the connecting circuit of the ultrasonic transducer is connected with an ultrasonic generator positioned outside the coal layer.
And the parts outside the coal seam drill holes of the water injection branch pipes are respectively provided with a stop valve.
A plurality of non-ultrasonic reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the non-ultrasonic reference drill holes, and hole openings of the non-ultrasonic reference drill holes are provided with hole packers; the water injection branch pipes in the non-ultrasonic reference drill holes respectively penetrate through the corresponding hole packers to extend out of the non-ultrasonic reference drill holes and are connected with the liquid injection main pipe; and the drill hole outer parts of the water injection branch pipes of the non-ultrasonic reference drill holes are respectively provided with a stop valve.
A plurality of sodium percarbonate-free reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the sodium percarbonate-free reference drill holes, and hole sealers are arranged at the orifices of the sodium percarbonate-free reference drill holes; the water injection branch pipes in the sodium percarbonate-free reference drill holes respectively penetrate through the corresponding hole packers and extend out of the sodium percarbonate-free reference drill holes; the outer part of each drilling hole of the water injection branch pipe without the sodium percarbonate reference drilling hole is provided with a stop valve, the water injection branch pipe without the sodium percarbonate reference drilling hole is connected with a water injection main pipe, the water injection main pipe is connected with a clean water tank, and a water injection pump is arranged on the water injection main pipe.
The invention also discloses an anti-reflection desorption-promoting experimental method carried out by using the synergistic anti-reflection desorption-promoting experimental system of the ultrasonic activated fracturing fluid, which is carried out according to the following steps in sequence:
step 1 is drilling:
specifically, drilling holes in a coal seam 1 in a roadway, wherein the coal seam drilling holes are used as hydraulic fracturing drilling holes and gas extraction drilling holes, and the distance between every two adjacent coal seam drilling holes is 5-60 meters;
particularly, water injection branch pipes are arranged in drilled holes of each coal seam, and each water injection branch pipe is connected with a liquid injection box through a liquid injection main pipe;
arranging ultrasonic transducers in the drill holes of the coal seams, wherein the ultrasonic transducers are connected to an ultrasonic generator through connecting lines; sealing the coal seam drilled hole by using a hole packer;
completing installation of a synergistic permeability-increasing desorption-promoting experimental system of the ultrasonic activated fracturing fluid at a coal seam;
step 3 is feeding:
adding industrial sodium percarbonate into a liquid injection box, and dissolving the industrial sodium percarbonate in water to obtain hydraulic fracturing fluid with the mass concentration of the sodium percarbonate of 0.1-10 per mill;
and step 4, low-pressure liquid injection:
opening a stop valve corresponding to each coal seam drilled hole, starting a liquid injection pump, setting the liquid injection pressure to be 4-10 MPa, injecting hydraulic fracturing liquid into each coal seam drilled hole, and infiltrating the hydraulic fracturing liquid into coal bodies through the original fractures of the coal seams under the pressure;
step 5, ultrasonic and sodium percarbonate synergistic permeability increasing and desorption promoting:
after the liquid injection pump displays that the liquid injection pressure reaches the preset liquid injection pressure, starting an ultrasonic generator in each coal seam drill hole, transmitting 35-40 kHz ultrasonic waves into the coal seam drill holes through an ultrasonic transducer, activating sodium percarbonate in hydraulic fracturing liquid, and enabling high-activity free radicals generated by activation to have an in-situ modification chemical effect with the surface of a coal body, so that the gas desorption rate of the coal body is increased and the mechanical strength of the coal body is reduced;
turning off the ultrasonic generator after each ultrasonic transducer works for 30-60 minutes;
step 6, hydraulic fracturing;
setting the injection pressure of an injection pump to be 35 MPa, performing hydraulic fracturing, and further percolating the activated hydraulic fracturing fluid to the deep part of the coal seam at the drilling hole of the coal seam under high pressure to modify more coal bodies in situ; recording the coal seam initiation pressure and the time for fracturing;
and step 7, finishing the anti-reflection desorption promotion operation:
when the pressure of the liquid injection pump is lower than 18MPa for 3 minutes continuously, the fracturing is finished, the synergistic permeability-increasing desorption-promoting experiment system for ultrasonically activating the fracturing liquid is removed, the hydraulic fracturing liquid is drained back, each fracturing extraction hole is connected to a gas extraction system to extract gas, and the gas extraction system monitors and records the extracted gas concentration and the extraction purity information of each drill hole.
Simultaneously, carrying out a non-ultrasonic contrast experiment and a non-sodium percarbonate contrast experiment, specifically:
a plurality of non-ultrasonic reference drill holes and a plurality of non-sodium percarbonate reference drill holes are also arranged in the coal seam, a water injection branch pipe is arranged in each non-ultrasonic reference drill hole, and a hole packer is arranged at the hole opening of each non-ultrasonic reference drill hole; the water injection branch pipes in the non-ultrasonic reference drill holes respectively penetrate through the corresponding hole packers and extend out of the non-ultrasonic reference drill holes; the outer part of each drill hole of the water injection branch pipe without the ultrasonic reference drill hole is respectively provided with a stop valve;
a plurality of sodium percarbonate-free reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the sodium percarbonate-free reference drill holes, and hole sealers are arranged at the orifices of the sodium percarbonate-free reference drill holes; the water injection branch pipes in the sodium percarbonate-free reference drill holes respectively penetrate through the corresponding hole packers and extend out of the sodium percarbonate-free reference drill holes; the outer part of each drilling hole of the water injection branch pipe of each sodium percarbonate-free reference drilling hole is provided with a stop valve, the water injection branch pipe of each sodium percarbonate-free reference drilling hole is connected with a water injection main pipe, the water injection main pipe is connected with a clear water tank, and a water injection pump is arranged on the water injection main pipe;
in the step 1, when a coal seam is drilled in a roadway, constructing a non-ultrasonic reference drilled hole and a non-sodium percarbonate reference drilled hole at the same time, wherein the non-ultrasonic reference drilled hole and the non-sodium percarbonate reference drilled hole are used as a hydraulic fracturing drilled hole and a gas extraction drilled hole;
collectively referring coal seam drilling holes, non-ultrasonic reference drilling holes and non-sodium percarbonate reference drilling holes as fracturing extraction holes, wherein the distance between every two adjacent fracturing extraction holes is 5-60 meters;
in the step 2, arranging water injection branch pipes in each non-ultrasonic reference drill hole and each non-sodium percarbonate reference drill hole, wherein the water injection branch pipes of the non-ultrasonic reference drill holes are connected with a liquid injection tank through a liquid injection main pipe, and the water injection branch pipes of the non-sodium percarbonate reference drill holes are connected with the water injection tank through a water injection main pipe;
arranging an ultrasonic transducer in the sodium percarbonate free reference drill hole, wherein the ultrasonic transducer is connected to an ultrasonic generator through a connecting line;
sealing the non-ultrasonic reference drill hole and the non-sodium percarbonate reference drill hole by using a hole packer;
in the step 3, adding water in a water injection tank to serve as the hydraulic fracturing fluid without sodium percarbonate;
hydraulic fracturing fluid seeps into coal body through the primary fractures of the coal bed under the pressure of 4-10 MPa;
in the step 5, starting an ultrasonic generator at each sodium percarbonate-free reference drill hole, enabling an ultrasonic transducer in each sodium percarbonate-free reference drill hole to emit 35-40 kHz ultrasonic waves, and enabling the ultrasonic waves and the hydraulic fracturing fluid without sodium percarbonate to act on the coal body simultaneously;
in step 6, for each non-ultrasonic reference borehole: the injection pressure of the injection pump is 35 MPa, hydraulic fracturing is carried out, hydraulic fracturing fluid further seeps to the deep part of the coal bed without the ultrasonic reference drilling hole under high pressure, and the coal body where the seepage passes is modified in situ;
for each sodium percarbonate free reference borehole: setting the water injection pressure of a water injection pump to be 35 MPa, performing hydraulic fracturing, and further percolating hydraulic fracturing fluid under high pressure to the deep part of the coal bed at the sodium percarbonate-free reference drilling hole;
in step 7, for each non-ultrasonic reference drilled hole, the parameter characteristic showing the end of fracturing is that the pressure of the liquid injection pump is lower than 18MPa for 3 minutes continuously;
for each sodium percarbonate free reference borehole, the parameter indicating the end of fracturing is characterized by a water injection pump pressure lower than 18MPa for 3 minutes.
Recording the fracture initiation pressure and the fracturing time of the coal bed at each non-ultrasonic reference drilling hole; the fracture initiation pressure and time taken to fracture were recorded for each reference drill hole without sodium percarbonate.
The invention has the following advantages:
the sodium percarbonate is an efficient and environment-friendly medicament, can be used for in-situ remediation of polluted sites after being activated, and has the advantages of high use safety, wide action range and no secondary pollution. The method utilizes the sodium percarbonate solution activated by ultrasonic to regulate and control the surface polarity of the coal body and reduce the mechanical strength of the coal body; the sodium percarbonate is introduced into the hydraulic fracturing fluid and is activated by adopting an ultrasonic technology, so that the surface polarity of the coal body can be regulated and controlled, the gas desorption of the coal bed is accelerated, the mechanical strength of the coal body is reduced, and the cracking and the crack expansion and extension of the coal body are promoted.
The essential difference from the conventional permeability-increasing technology is that the permeability-increasing technology not only increases the permeability of the coal bed, but also accelerates the gas desorption of the coal bed, is a technology for promoting the desorption and permeability-increasing to be integrated, can extract more gas from the coal bed, further reduces the risk of coal and gas outburst accidents, and improves the recovery and utilization rate of the gas. In the prior technical scheme for increasing the permeability of the coal bed, the desorption rate of coal bed gas is not improved, only the coal bed cracks are simply expanded or extended, the gas can conveniently flow out along the cracks, and the desorption promoting effect is not provided.
The synergistic permeability-increasing desorption-promoting experimental system for the ultrasonic activated fracturing fluid is simple in structure and convenient for permeability-increasing desorption-promoting operation. The setting of each stop valve is convenient for carry out the anti-reflection to partial coal seam drilling according to actual conditions. Especially when a plurality of coal seam drill holes are simultaneously subjected to anti-reflection desorption promotion operation, the completion time of each coal seam drill hole is asynchronous, and the stop valve can be arranged to complete the closing of one corresponding stop valve in one coal seam drill hole.
And an ultrasonic transducer is not arranged in the non-ultrasonic reference drill hole, so that the anti-reflection and desorption promotion effects in the absence of ultrasonic synergistic action can be conveniently compared. In the invention, the ultrasonic wave can activate the sodium percarbonate, and the high-activity free radicals generated by the activation have chemical action with the surface of the coal body, change the polarity of the surface of the coal body and reduce the mechanical strength of the coal body, so the anti-reflection and desorption-promotion effects under the synergistic action of the ultrasonic wave and the sodium percarbonate aqueous solution are far stronger than the effects under the non-synergistic action.
The sodium percarbonate solution, not the sodium percarbonate aqueous solution, but water is introduced into the sodium percarbonate-free reference drill hole, so that the anti-reflection and desorption-promoting effects in the absence of the synergistic effect of sodium percarbonate can be compared conveniently.
The method for the permeability-increasing desorption-promoting experiment is convenient to implement, can be directly applied to coal seam mining practice after the ultrasonic-free contrast experiment and the sodium percarbonate-free contrast experiment in claim 6 are omitted (the technical scheme in claim 5), can be directly used as a method for permeability-increasing desorption-promoting of an actual coal seam, promotes coal seam gas desorption while increasing the permeability of the coal seam, greatly improves the volume fraction of gas to be pumped and discharged, greatly improves the daily extraction purity, shortens the fracturing time so as to improve the time efficiency of gas extraction, reduces the fracture initiation pressure so as to reduce the electric energy consumed by a pump in hydraulic fracturing operation, has the remarkable technical effects of saving energy, reducing consumption, improving the time efficiency of gas extraction, improving the gas extraction quantity and the like on the whole, and has good popularization and application values.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Detailed Description
As shown in fig. 1, the synergistic permeability-increasing desorption-promoting experimental system for the ultrasonic activated fracturing fluid comprises a plurality of coal seam drill holes 1 arranged in a coal seam 3, wherein a water injection branch pipe 2 and an ultrasonic transducer 4 are arranged in each coal seam drill hole 1; a hole packer 5 is arranged at the hole opening of each coal seam drilled hole 1; connecting lines of the water injection branch pipes 2 and the ultrasonic transducers 4 in the coal seam drill holes 1 penetrate through corresponding hole packers 5 and extend out of the coal seam drill holes 1;
the water injection branch pipe 2 extends out of the coal seam drilling hole 1 and is connected with a liquid injection main pipe 6, the liquid injection main pipe 6 is connected with a liquid injection box 7, a sodium percarbonate aqueous solution for promoting the gas desorption of the coal seam 3 under the action of ultrasonic waves is contained in the liquid injection box 7, and the mass concentration of the sodium percarbonate is 0.1-10 permillage (including two end values); the liquid injection main pipe 6 is provided with a liquid injection pump 8; the connecting line of the ultrasonic transducer 4 is connected with an ultrasonic generator 9 positioned outside the coal seam 3. The connection line of the ultrasonic transducer 4 is preferably a pressure-resistant waterproof cable. The synergistic permeability-increasing desorption-promoting experimental system for the ultrasonic activated fracturing fluid is simple in structure and convenient for permeability-increasing desorption-promoting operation.
And stop valves 11 are respectively arranged at the parts of the water injection branch pipes 2 outside the coal seam drill holes 1. The arrangement of each stop valve 11 is convenient for carry out the anti-reflection to partial coal seam drilling 1 according to actual conditions. Especially, when a plurality of coal seam drill holes 1 are subjected to anti-reflection desorption promotion operation at the same time, the completion time of each coal seam drill hole 1 is asynchronous, and one stop valve 11 can be closed by one coal seam drill hole 1 due to the arrangement of the stop valves 11.
A plurality of non-ultrasonic reference drill holes 10 are further formed in the coal seam 3, water injection branch pipes 2 are arranged in the non-ultrasonic reference drill holes 10, and hole packers 5 are arranged at orifices of the non-ultrasonic reference drill holes 10; the water injection branch pipes 2 in the non-ultrasonic reference drill holes 10 respectively penetrate through the corresponding hole packers 5 to extend out of the non-ultrasonic reference drill holes 10 and are connected with the liquid injection main pipe 6; the drill hole outer parts of the water injection branch pipes 2 of the non-ultrasonic reference drill holes 10 are respectively provided with a stop valve 11.
The ultrasonic transducer 4 is not arranged in the ultrasonic-free reference drill hole 10, so that the anti-reflection and desorption promotion effects in the absence of ultrasonic synergistic effect can be compared conveniently. In the invention, the ultrasonic wave can activate the sodium percarbonate, and the high-activity free radicals generated by the activation have chemical action with the surface of the coal body, change the polarity of the surface of the coal body and reduce the mechanical strength of the coal body, so the anti-reflection and desorption-promotion effects under the synergistic action of the ultrasonic wave and the sodium percarbonate aqueous solution are far stronger than the effects under the non-synergistic action.
A plurality of sodium percarbonate-free reference drill holes 12 are also formed in the coal seam 3, water injection branch pipes 2 are arranged in the sodium percarbonate-free reference drill holes 12, and hole openings of the sodium percarbonate-free reference drill holes 12 are provided with hole packers 5; the water injection branch pipes 2 in each sodium percarbonate-free reference drilling hole 12 respectively penetrate through the corresponding hole packers 5 and extend out of the sodium percarbonate-free reference drilling holes 12; the outer part of the water injection branch pipe 2 of each sodium percarbonate-free reference drill hole 12 is provided with a stop valve 11, the water injection branch pipe 2 of each sodium percarbonate-free reference drill hole 12 is connected with a water injection main pipe 13, the water injection main pipe 13 is connected with a clean water tank 14, and the water injection main pipe 13 is provided with a water injection pump 15.
The sodium percarbonate-free reference borehole 12 is filled with water instead of a sodium percarbonate aqueous solution, so that the anti-reflection and desorption promotion effects in the absence of sodium percarbonate can be compared conveniently.
The invention also discloses an anti-reflection desorption-promoting experimental method carried out by using the synergistic anti-reflection desorption-promoting experimental system of the ultrasonic activated fracturing fluid, which is carried out according to the following steps in sequence:
step 1 is drilling:
specifically, coal seam drill holes 1 are constructed in a roadway towards a coal seam 3, the coal seam drill holes 1 are used as hydraulic fracturing drill holes and gas extraction drill holes, and the distance between every two adjacent coal seam drill holes 1 is 5-60 meters (including two end values);
specifically, water injection branch pipes 2 are arranged in drilled holes 1 of each coal seam, and each water injection branch pipe 2 is connected with a liquid injection box 7 through a liquid injection main pipe 6;
arranging an ultrasonic transducer 4 in each coal seam drilling hole 1, wherein the ultrasonic transducer 4 is connected to an ultrasonic generator 9 through a connecting line; sealing the coal seam drilled hole 1 by using a hole packer 5; completing installation of a synergistic permeability-increasing desorption-promoting experimental system of the ultrasonic activated fracturing fluid at the coal seam 3;
step 3 is feeding:
adding industrial sodium percarbonate into a liquid injection box 7, and dissolving the industrial sodium percarbonate in water to obtain hydraulic fracturing fluid with the mass concentration of the sodium percarbonate of 0.1-10 per mill;
and step 4, low-pressure liquid injection:
opening a stop valve 11 corresponding to each coal seam drilled hole 1, starting a liquid injection pump 8, setting liquid injection pressure to be 4-10 MPa (including two end values), injecting hydraulic fracturing liquid into each coal seam drilled hole 1, and infiltrating the hydraulic fracturing liquid into coal bodies through primary fractures of the coal seam 3 under the pressure;
step 5, ultrasonic and sodium percarbonate synergistic permeability increasing and desorption promoting:
after the liquid injection pump 8 displays that the liquid injection pressure reaches the preset liquid injection pressure, starting the ultrasonic transducers 4 in the coal seam drill holes 1, transmitting 35-40 kHz ultrasonic waves into the coal seam drill holes 1 through the ultrasonic transducers 4, activating sodium percarbonate in hydraulic fracturing liquid, and enabling high-activity free radicals generated by activation to have in-situ modification chemical action with the surfaces of coal bodies, so that the gas desorption rate of the coal bodies is increased and the mechanical strength of the coal bodies is reduced;
after each ultrasonic transducer 4 works for 30-60 minutes (including both values), the ultrasonic generator 9 is turned off so as to turn off each ultrasonic transducer 4;
step 6, hydraulic fracturing;
the fracture initiation pressure of the common coal seam 3 hydraulic fracturing is 25-30 MPa, for the sake of stability, the injection pressure of the injection pump 8 is set to be 35 MPa, hydraulic fracturing is carried out, the activated hydraulic fracturing fluid further seeps to the deep part of the coal seam 3 at the coal seam drilling hole 1 under high pressure, and more coal bodies are modified in situ on the basis of the step 5; recording the coal seam initiation pressure and the time for fracturing;
and step 7, finishing the anti-reflection desorption promotion operation:
when the pressure of the liquid injection pump 8 is lower than 18MPa for 3 minutes continuously, the fracturing is finished, the synergistic permeability-increasing desorption-promoting experiment system of the ultrasonic activated fracturing liquid is removed, the hydraulic fracturing liquid is drained back, each fracturing extraction hole is connected to a gas extraction system to conduct gas extraction, and the gas extraction concentration and extraction purity information of each drilled hole are monitored and recorded through the gas extraction system.
The gas extraction system is provided with a gas detector and other devices, and is preferably provided with a CGWZ-100 (A) -Z type pipeline gas comprehensive parameter measuring instrument produced by optotechnology limited. The monitoring and recording of the gas extraction concentration and the extraction purity information of each borehole by the gas extraction system is a conventional technology, and the gas extraction system is not described in detail.
In the process of the anti-reflection desorption-promoting experimental method, a non-ultrasonic contrast experiment and a non-sodium percarbonate contrast experiment are carried out at the same time, and the method specifically comprises the following steps:
in the step 1, when a coal seam drill hole 1 is constructed in a roadway to a coal seam 3, an ultrasonic-free reference drill hole 10 and a sodium percarbonate-free reference drill hole 12 are constructed at the same time, and the ultrasonic-free reference drill hole 10 and the sodium percarbonate-free reference drill hole 12 are used as a hydraulic fracturing drill hole and a gas extraction drill hole;
the coal seam drilled hole 1, the non-ultrasonic reference drilled hole 10 and the non-sodium percarbonate reference drilled hole 12 are collectively called as fracturing extraction holes, and the distance between adjacent fracturing extraction holes is 5-60 meters (including both end values);
in the step 2, water injection branch pipes 2 are arranged in each non-ultrasonic reference drill hole 10 and each non-sodium percarbonate reference drill hole 12, the water injection branch pipes 2 of the non-ultrasonic reference drill holes 10 are connected with a water injection tank 7 through a water injection main pipe 6, and the water injection branch pipes 2 of the non-sodium percarbonate reference drill holes 12 are connected with a water injection tank 14 through a water injection main pipe 13;
arranging an ultrasonic transducer 4 in the sodium percarbonate free reference borehole 12, where the ultrasonic transducer 4 is connected to an ultrasonic generator 9 by a connection line;
sealing the non-ultrasonic reference borehole 10 and the non-sodium percarbonate reference borehole 12 by means of a hole packer 5;
in step 3, water is added into the water injection tank 14 to be used as the hydraulic fracturing fluid without sodium percarbonate;
in the step 4, opening the stop valves 11 corresponding to the non-ultrasonic reference drill holes 10 and the non-sodium percarbonate reference drill holes 12, starting the water injection pump 15, setting the water injection pressure to be 4-10 MPa (including two end values), injecting the hydraulic fracturing fluid containing sodium percarbonate into the non-ultrasonic reference drill holes 10 by the liquid injection pump 8, and injecting the hydraulic fracturing fluid containing no sodium percarbonate into the non-sodium percarbonate reference drill holes 12 by the water injection pump 15;
the hydraulic fracturing fluid seeps into the coal body through the primary fracture of the coal bed 3 under the pressure of 4-10 MPa;
in the step 5, the ultrasonic generators 9 at the positions of the sodium percarbonate-free reference drill holes 12 are started, the ultrasonic transducers 4 in the sodium percarbonate-free reference drill holes 12 also emit 35-40 kHz ultrasonic waves, and the ultrasonic waves and the hydraulic fracturing fluid without sodium percarbonate simultaneously act on the coal body; providing conditions for obtaining comparison data;
in step 6, for each non-ultrasonic reference borehole 10: the injection pressure of the injection pump is 35 MPa, hydraulic fracturing is carried out, hydraulic fracturing fluid further seeps to the 3 deep part of the coal bed at the 10-position of the non-ultrasonic reference drill hole under high pressure, and the coal body where seepage passes is modified in situ;
for each sodium percarbonate free reference borehole 12: setting the water injection pressure of a water injection pump 15 to be 35 MPa, performing hydraulic fracturing, and further percolating the hydraulic fracturing fluid under high pressure to the deep part of the coal seam 3 at the sodium percarbonate-free reference drill hole 12;
in step 7, for each non-ultrasonic reference borehole 10, the parameter characteristic showing the end of fracturing is that the pressure of the liquid injection pump 8 is lower than 18MPa for 3 minutes continuously;
for each sodium percarbonate free reference borehole, the parameter indicating the end of fracturing is characterized by a pressure of the water injection pump 15 lower than 18MPa for 3 minutes.
Recording the fracture initiation pressure and the time for fracturing of the coal seam at each non-ultrasonic reference drill hole 10; the coal seam initiation pressure and time taken to fracture at each sodium percarbonate free reference borehole 12 were recorded.
Table 1, borehole fracturing parameters and gas drainage records:
as can be seen from the data in the table 1, by adopting the ultrasonic activation fracturing fluid in-situ modification coal body strengthening gas extraction method, the fracture initiation pressure of a coal bed can be reduced by about 5MPa compared with that of a coal bed which only adopts a sodium percarbonate solution without adopting ultrasonic waves, the fracturing time is reduced by about 20 minutes, the volume fraction increase of the extracted gas is more than 21% (more than doubling), and the daily extracted gas purity is improved to about 3 times.
As can be seen from the data in the table 1, by adopting the ultrasonic activation fracturing fluid in-situ modification coal body strengthening gas extraction method, compared with the coal bed adopting ultrasonic wave and hydraulic fracturing but not adopting a sodium percarbonate solution, the fracture initiation pressure of the coal bed can be reduced by about 4MPa, the fracturing time is reduced by about 20 minutes, the volume fraction increase of the extracted gas reaches more than 18 percent (at least doubled), and the daily extracted gas purity is increased to 2-4 times.
The invention can obviously reduce the outburst danger of coal and gas, improve the gas drainage efficiency, save the production cost, has great progress compared with the existing hydraulic fracturing reinforced coal seam gas drainage technology, and has wide practicability in the technical field.
The analysis considers that: the technology generates high-activity free radicals by activating sodium percarbonate in hydraulic fracturing fluid through ultrasonic waves, carries out in-situ modification on the surface of a coal bed, and accelerates the desorption of coal bed gas by regulating and controlling the polarity of the surface of coal; the coal bed surface is modified to facilitate the coal body to absorb the activated fracturing fluid, the ultrasonic wave activates sodium percarbonate to make the fracturing fluid alkaline (pH = 10-11), and the mechanical strength of the coal body is obviously reduced after the sodium percarbonate acts on the coal bed, the coal bed fracture initiation pressure is reduced, and the fracture coal penetration length is increased; the ultrasonic wave generates a local heat effect at a coal-water interface, the thermal stress of a coal body promotes the crack to expand and extend, the further seepage of the fracturing fluid to the deep part of the coal bed is promoted, and the fracturing fluid and hydraulic fracturing are cooperated to form a net-shaped crack, so that the seepage and the migration of coal bed gas are facilitated.
The applicant also performs comparison experiments on the contact angle of the coal surface and the mechanical properties of the coal body after being wetted by different fracturing fluids aiming at the same coal sample, and the results are shown in table 2:
table 2, coal surface contact angles and coal mechanical properties after the coal samples were wetted with different fracturing fluids:
as can be seen from table 2, the use of ultrasonic wave (+ clean water) alone or industrial sodium percarbonate alone only slightly affects the surface polarity of coal and the mechanical strength of coal, while the use of ultrasonic activated sodium percarbonate fracturing fluid can significantly increase the surface polarity of coal (the contact angle is reduced by more than 27% compared with no treatment) and significantly reduce the mechanical strength of coal (the uniaxial compressive strength is reduced by more than 39.8% compared with no treatment).
Claims (6)
1. Ultrasonic activation fracturing fluid's short desorption experimental system of synergistic anti-reflection, including setting up a plurality of coal seam drilling in the coal seam, its characterized in that: a water injection branch pipe and an ultrasonic transducer are arranged in each coal seam drill hole; a hole packer is arranged at the hole of each coal seam drill hole; the water injection branch pipes in the coal seam drill holes and the connecting lines of the ultrasonic transducers penetrate through the corresponding hole packers and extend out of the coal seam drill holes;
the water injection branch pipe extends out of the coal seam drill hole and is connected with a liquid injection main pipe, the liquid injection main pipe is connected with a liquid injection box, sodium percarbonate water solution used for promoting coal seam gas desorption under the action of ultrasonic waves is contained in the liquid injection box, and the mass concentration of the sodium percarbonate is 0.1-10 per mill; the liquid injection main pipe is provided with a liquid injection pump; the connecting circuit of the ultrasonic transducer is connected with an ultrasonic generator positioned outside the coal layer.
2. The system for the synergistic permeability-increasing desorption-promoting experiment of the ultrasonic-activated fracturing fluid, according to claim 1, is characterized in that: and the parts outside the coal seam drill holes of the water injection branch pipes are respectively provided with a stop valve.
3. The system for the experiment on the synergistic permeability-increasing and desorption-promoting of the ultrasonic-activated fracturing fluid, according to claim 1 or 2, is characterized in that: a plurality of non-ultrasonic reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the non-ultrasonic reference drill holes, and hole openings of the non-ultrasonic reference drill holes are provided with hole packers; the water injection branch pipes in the non-ultrasonic reference drill holes respectively penetrate through the corresponding hole packers to extend out of the non-ultrasonic reference drill holes and are connected with the liquid injection main pipe; and the drill hole outer parts of the water injection branch pipes of the non-ultrasonic reference drill holes are respectively provided with a stop valve.
4. The system for the synergistic permeability-increasing desorption-promoting experiment of the ultrasonic-activated fracturing fluid, according to claim 3, is characterized in that: a plurality of sodium percarbonate-free reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the sodium percarbonate-free reference drill holes, and hole sealers are arranged at the orifices of the sodium percarbonate-free reference drill holes; the water injection branch pipes in the sodium percarbonate-free reference drill holes respectively penetrate through the corresponding hole packers and extend out of the sodium percarbonate-free reference drill holes; the outer part of each drilling hole of the water injection branch pipe without the sodium percarbonate reference drilling hole is provided with a stop valve, the water injection branch pipe without the sodium percarbonate reference drilling hole is connected with a water injection main pipe, the water injection main pipe is connected with a clean water tank, and a water injection pump is arranged on the water injection main pipe.
5. An anti-reflection desorption-promoting experimental method carried out by using the synergistic anti-reflection desorption-promoting experimental system of the ultrasonic activated fracturing fluid in the claim 2 is characterized by sequentially carrying out the following steps:
step 1 is drilling:
specifically, drilling holes in a coal seam 1 in a roadway, wherein the coal seam drilling holes are used as hydraulic fracturing drilling holes and gas extraction drilling holes, and the distance between every two adjacent coal seam drilling holes is 5-60 meters;
step 2, installing a synergistic permeability-increasing desorption-promoting experimental system of the ultrasonic activated fracturing fluid:
particularly, water injection branch pipes are arranged in drilled holes of each coal seam, and each water injection branch pipe is connected with a liquid injection box through a liquid injection main pipe;
arranging ultrasonic transducers in the drill holes of the coal seams, wherein the ultrasonic transducers are connected to an ultrasonic generator through connecting lines; sealing the coal seam drilled hole by using a hole packer;
completing installation of a synergistic permeability-increasing desorption-promoting experimental system of the ultrasonic activated fracturing fluid at a coal seam;
step 3 is feeding:
adding industrial sodium percarbonate into a liquid injection box, and dissolving the industrial sodium percarbonate in water to obtain hydraulic fracturing fluid with the mass concentration of the sodium percarbonate of 0.1-10 per mill;
and step 4, low-pressure liquid injection:
opening a stop valve corresponding to each coal seam drilled hole, starting a liquid injection pump, setting the liquid injection pressure to be 4-10 MPa, injecting hydraulic fracturing liquid into each coal seam drilled hole, and infiltrating the hydraulic fracturing liquid into coal bodies through the original fractures of the coal seams under the pressure;
step 5, ultrasonic and sodium percarbonate synergistic permeability increasing and desorption promoting:
after the liquid injection pump displays that the liquid injection pressure reaches the preset liquid injection pressure, starting an ultrasonic generator in each coal seam drill hole, transmitting 35-40 kHz ultrasonic waves into the coal seam drill holes through an ultrasonic transducer, activating sodium percarbonate in hydraulic fracturing liquid, and enabling high-activity free radicals generated by activation to have an in-situ modification chemical effect with the surface of a coal body, so that the gas desorption rate of the coal body is increased and the mechanical strength of the coal body is reduced;
turning off the ultrasonic generator after each ultrasonic transducer works for 30-60 minutes;
step 6, hydraulic fracturing;
setting the injection pressure of an injection pump to be 35 MPa, performing hydraulic fracturing, and further percolating the activated hydraulic fracturing fluid to the deep part of the coal seam at the drilling hole of the coal seam under high pressure to modify more coal bodies in situ; recording the coal seam initiation pressure and the time for fracturing;
and step 7, finishing the anti-reflection desorption promotion operation:
when the pressure of the liquid injection pump is lower than 18MPa for 3 minutes continuously, the fracturing is finished, the synergistic permeability-increasing desorption-promoting experiment system for ultrasonically activating the fracturing liquid is removed, the hydraulic fracturing liquid is drained back, each fracturing extraction hole is connected to a gas extraction system to extract gas, and the gas extraction system monitors and records the extracted gas concentration and the extraction purity information of each drill hole.
6. The experimental method for permeability increase and desorption promotion according to claim 5, wherein:
simultaneously, carrying out a non-ultrasonic contrast experiment and a non-sodium percarbonate contrast experiment, specifically:
a plurality of non-ultrasonic reference drill holes and a plurality of non-sodium percarbonate reference drill holes are also arranged in the coal seam, a water injection branch pipe is arranged in each non-ultrasonic reference drill hole, and a hole packer is arranged at the hole opening of each non-ultrasonic reference drill hole; the water injection branch pipes in the non-ultrasonic reference drill holes respectively penetrate through the corresponding hole packers and extend out of the non-ultrasonic reference drill holes; the outer part of each drill hole of the water injection branch pipe without the ultrasonic reference drill hole is respectively provided with a stop valve;
a plurality of sodium percarbonate-free reference drill holes are also formed in the coal seam, water injection branch pipes are arranged in the sodium percarbonate-free reference drill holes, and hole sealers are arranged at the orifices of the sodium percarbonate-free reference drill holes; the water injection branch pipes in the sodium percarbonate-free reference drill holes respectively penetrate through the corresponding hole packers and extend out of the sodium percarbonate-free reference drill holes; the outer part of each drilling hole of the water injection branch pipe of each sodium percarbonate-free reference drilling hole is provided with a stop valve, the water injection branch pipe of each sodium percarbonate-free reference drilling hole is connected with a water injection main pipe, the water injection main pipe is connected with a clear water tank, and a water injection pump is arranged on the water injection main pipe;
in the step 1, when a coal seam is drilled in a roadway, constructing a non-ultrasonic reference drilled hole and a non-sodium percarbonate reference drilled hole at the same time, wherein the non-ultrasonic reference drilled hole and the non-sodium percarbonate reference drilled hole are used as a hydraulic fracturing drilled hole and a gas extraction drilled hole;
collectively referring coal seam drilling holes, non-ultrasonic reference drilling holes and non-sodium percarbonate reference drilling holes as fracturing extraction holes, wherein the distance between every two adjacent fracturing extraction holes is 5-60 meters;
in the step 2, arranging water injection branch pipes in each non-ultrasonic reference drill hole and each non-sodium percarbonate reference drill hole, wherein the water injection branch pipes of the non-ultrasonic reference drill holes are connected with a liquid injection tank through a liquid injection main pipe, and the water injection branch pipes of the non-sodium percarbonate reference drill holes are connected with the water injection tank through a water injection main pipe;
arranging an ultrasonic transducer in the sodium percarbonate free reference drill hole, wherein the ultrasonic transducer is connected to an ultrasonic generator through a connecting line;
sealing the non-ultrasonic reference drill hole and the non-sodium percarbonate reference drill hole by using a hole packer;
in the step 3, adding water in a water injection tank to serve as the hydraulic fracturing fluid without sodium percarbonate;
step 4, opening stop valves corresponding to the non-ultrasonic reference drill holes and the non-sodium percarbonate reference drill holes, starting a water injection pump while starting a liquid injection pump, setting water injection pressure to be 4-10 MPa, injecting a hydraulic fracturing fluid containing sodium percarbonate into the non-ultrasonic reference drill holes by the liquid injection pump, and injecting a hydraulic fracturing fluid containing no sodium percarbonate into the non-sodium percarbonate reference drill holes by the water injection pump;
hydraulic fracturing fluid seeps into coal body through the primary fractures of the coal bed under the pressure of 4-10 MPa;
in the step 5, starting an ultrasonic generator at each sodium percarbonate-free reference drill hole, enabling an ultrasonic transducer in each sodium percarbonate-free reference drill hole to emit 35-40 kHz ultrasonic waves, and enabling the ultrasonic waves and the hydraulic fracturing fluid without sodium percarbonate to act on the coal body simultaneously;
in step 6, for each non-ultrasonic reference borehole: the injection pressure of the injection pump is 35 MPa, hydraulic fracturing is carried out, hydraulic fracturing fluid further seeps to the deep part of the coal bed without the ultrasonic reference drilling hole under high pressure, and the coal body where the seepage passes is modified in situ;
for each sodium percarbonate free reference borehole: setting the water injection pressure of a water injection pump to be 35 MPa, performing hydraulic fracturing, and further percolating hydraulic fracturing fluid under high pressure to the deep part of the coal bed at the sodium percarbonate-free reference drilling hole;
in step 7, for each non-ultrasonic reference drilled hole, the parameter characteristic showing the end of fracturing is that the pressure of the liquid injection pump is lower than 18MPa for 3 minutes continuously;
for each sodium percarbonate free reference borehole, the parameter characteristic indicating the end of fracturing is that the pressure of the water injection pump is lower than 18MPa for 3 minutes continuously;
recording the fracture initiation pressure and the fracturing time of the coal bed at each non-ultrasonic reference drilling hole; the fracture initiation pressure and time taken to fracture were recorded for each reference drill hole without sodium percarbonate.
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