• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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  • 优先权
    • 专利摘要:
    The invention provides a hydraulic fracturing fluid for fracturing and enhancing permeability for coal seams, including a first component and a second component. The first component is an aqueous solution of persulfate. The second component is a mixture of water and porous carbon containing transition metal ions. The invention further discloses a gas extraction system and a gas extraction method. During hydraulic fracturing, the hydraulic fracturing fluid and the organic matters with different molecular weights in coal seams continuously perform oxidation and in-situ modification reactions in a wide temperature range, thereby partially dissolving organic matters with low molecular weight, dredging the fractures and pores in coal seams, and reducing methane adsorbability of the coal seams. Therefore, the gas absorbed in coal seams is converted to free gas, greatly improving the permeability enhancement effect of coal seams compared with the simple hydraulic fracturing in the prior art.
    公开号:NL2025333A
    申请号:NL2025333
    申请日:2020-04-10
    公开日:2021-02-01
    发明作者:Yang Juan；Wei Jianping；Dai Jun
    申请人:Univ Henan Polytechnic；
    IPC主号:
    专利说明:

    HYDRAULIC FRACTURING FLUID, GAS EXTRACTION SYSTEM AND GAS
    EXTRACTION METHOD CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority from Chinese Patent Application No. 201910621623.3, filed on July 10, 2019. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.
    TECHNICAL FIELD This application relates to coal mining technique, and more particularly to the permeability enhancement and gas extraction in coal reservoirs.
    BACKGROUND OF THE INVENTION Coal mine gas is the main factor that causes coal mine disasters, but it is a non- renewable clean energy. The simultaneous extraction of coal and gas is the basic technique to prevent gas outbursts and achieve resource utilization.
    In China, coal seams generally have large gas contents, strong adsorption and low permeability. Most coal seam gas is stored in an adsorbed state on the inner surface of pores in coal matrices, and only a small amount of the coal seam gas dissociates in cleats and fractures. The coal mine gas is mainly extracted by means of borehole extraction, and the extraction efficiency thereof mainly depends on the permeability of the coal. Therefore, it is effective to increase the permeability of coal reservoirs to realize the simultaneous extraction of coal and gas.
    As the mine depth continues to increase, the permeability of the coal increasingly limits the gas extraction. Efficient techniques for enhancing the permeability of coal reservoirs are essential for the safe production of coal mine and gas extraction in coal seams. In order to enhance the permeability of coal reservoirs, many studies have been carried out, such as hydraulic fracturing, high-pressure gas fracturing, microwave fracturing and chemical permeability enhancement. However,
    existing physical permeability enhancements such as hydraulic fracturing, high- pressure gas fracturing and microwave fracturing are mainly applied to coal seams which are harder and have better air permeability; and existing chemical permeability enhancements have problems such as low efficiency, serious environmental pollution, poor stability of permeability enhancement agents and strong toxicity.
    Therefore, it is necessary to develop a high-efficient, safe and stable chemical permeability enhancement method to improve the permeability of coal seams to promote gas extraction.
    SUMMARY OF THE INVENTION An object of the invention is to provide a hydraulic fracturing fluid for improving gas extraction efficiency.
    To achieve the above-mentioned object, the invention provides a hydraulic fracturing fluid for fracturing and enhancing permeability of a coal seam, which comprises a first component and a second component, wherein the first component is an aqueous solution of persulfate; the second component is a mixture of water and porous carbon containing transition metal ions; and based on the hydraulic fracturing fluid, the first component is 0.9-1.1 parts by volume, and the second component is
    0.9-1.1 parts by volume.
    In some embodiments, based on the hydraulic fracturing fluid, the first component is 1 part by volume, and the second component is 1 part by volume.
    In some embodiments, the persulfate in the first component is ammonium persulfate and/or sodium persulfate and/or calcium persulfate and/or potassium persulfate; and the first component comprises 1-25 parts by weight of persulfate and 100 parts by weight of water.
    In some embodiments, the porous carbon containing transition metal ions in the second component is prepared by a method comprising steps of: mixing transition metal salt with aromatic carboxylic acid in a ball mill to obtain a mixture, and calcining the mixture in an inert atmosphere at high temperature to obtain the porous carbon containing transition metal ions;
    wherein the transition metal salt is nickel nitrate and/or manganese chloride and/or cobalt nitrate and/or copper sulfate and/or zinc nitrate; the aromatic carboxylic acid is benzenetricarboxylic acid and/or terephthalic acid and derivatives thereof and/or p-hydroxybenzoic acid and/or p-aminobenzoic acid; the inert atmosphere is nitrogen or argon, and a calcining temperature is 500-1000 °C; the transition metal salt is 0.8-1.2 parts by weight, and the aromatic carboxylic acid is 0.8-1.2 parts by weight; and the second component comprises not more than 25 parts by weight of the porous carbon containing transition metal ions and 100 parts by weight of water.
    The invention further discloses a gas extraction system using the hydraulic fracturing fluid, which comprises a fracturing borehole and a plurality of extraction boreholes provided between a roof and a floor of the coal seam; wherein the fracturing borehole has a fractured area in the coal seam, and the extraction boreholes are provided in the fractured area at left and right sides of the fracturing borehole, respectively; a fracturing pipe is inserted in the fracturing borehole, and an extraction pipe is inserted in each of the extraction boreholes; a fluid inlet is provided on the fracturing pipe, and a gas outlet is provided on the extraction pipe; the fracturing pipe reaches downward out of the floor of the coal seam and is connected to a mixer; the mixer is provided with a first inlet, a second inlet and an outlet; the outlet of the mixer is connected to the fracturing pipe, the first inlet of the mixer is connected to a first component feeder, and the second inlet of the mixer is connected to a second component feeder; the fracturing pipe between the mixer and the fracturing borehole is connected with a pressure gauge and a discharge pipe provided with a discharge valve; and the extraction pipe reaches downward out of the floor of the coal seam and is connected to a main extraction pipe which is connected to a gas extractor and provided with a main extraction valve, and an extraction valve is provided on the extraction pipe.
    In some embodiments, the first component feeder comprises a first component feed tank which is connected to a first component feed pump via a first outlet pipe; an outlet of the first component feed pump is connected to the first inlet of the mixer via a first component feed pipe, and a first component feed valve is provided on the first component feed pipe; and the second component feeder comprises a second component feed tank which is connected to a second component feed pump via a second outlet pipe; an outlet of the second component feed pump is connected to the second inlet of the mixer via a second component feed pipe, and a second component feed valve is provided on the second component feed pipe.
    In some embodiments, an ultrasonic vibration plate is provided on a bottom of the second component feed tank, and an ultrasonic generator is provided on the ultrasonic vibration plate.
    The invention further discloses a gas extraction method using the gas extraction system, which comprises: (1) preparation (1.1) drilling and preparing the hydraulic fracturing fluid drilling one fracturing borehole and two extraction boreholes by a drilling rig from the floor to the roof of the coal seam, so that the two extraction boreholes are located in the fractured area at two sides of the fracturing borehole, respectively; preparing the first component: dissolving 1-25 parts by weight of persulfate in 100 parts by weight of water to obtain the first component and storing the first component in the first component feed tank; and preparing the second component: mixing transition metal salt with aromatic carboxylic acid to obtain a mixture, calcining the mixture in an inert atmosphere at high temperature to obtain the porous carbon containing transition metal ions; placing the porous carbon containing transition metal ions in water to obtain the second component and storing the second component in the second component feed tank; and turning on the ultrasonic generator on the ultrasonic vibration plate, so that the porous carbon containing transition metal ions evenly disperses in water inthe second component feed tank;
    (1.2) arranging fracturing equipment and extraction equipment pre-installing the pressure gauge and the discharge pipe on a part of the fracturing pipe out of the fracturing borehole, and pre-installing the discharge valve on the discharge pipe; and pre-installing the main extraction valve on the main
    5 extraction pipe, and pre-installing the extraction valve on the extraction pipe;
    placing the fracturing pipe in the fracturing borehole, such that one end of the fracturing pipe reaches the roof of the coal seam, and the other end of the fracturing pipe, out of the fracturing borehole, is connected to the outlet of the mixer;
    connecting individual parts of the first component feeder, and connecting the first component feed pipe to the first inlet of the mixer;
    connecting individual parts of the second component feeder, and connecting the second component feed pipe to the second inlet of the mixer; and arranging the extraction equipment: placing the extraction pipe in each of the extraction boreholes, such that one end of the extraction pipe reaches the roof of the coal seam, and the other end of the extraction pipe, out of each of the extraction boreholes, is connected to the main extraction pipe; connecting the main extraction pipe to the gas extractor;
    (2) hole sealing sealing openings of the fracturing and extraction boreholes by a hole packer; (3) hydraulic fracturing closing the discharge valve; opening the first and second component feed valves, and the first and second component feed pumps; pumping the first and second components to the fracturing borehole at the same time to fracture the coal seam to enhance permeability thereof;
    recording an initial pressure in the fracturing pipe by reading the pressure gauge within 5 min after the first and second component feed pumps are turned on, wherein the initial pressure is 25-30 MPa;
    continuously observing the pressure gauge; when a pressure in the fracturing pipe drops to 15+3 MPa and remains not more than 18 MPa for 5 min, closing the first and second component feed valves, and the first and second component feed pumps; and opening the discharge valve to release the pressure in the fracturing pipe; when the pressure reading on the pressure gauge returns to atmospheric pressure, closing the discharge valve; and (4) gas extracting opening the main extraction valve and extraction valves, starting the gas extractor to extract gas in the extraction boreholes and storing the gas; observing the gas extraction volume per unit time via the gas extractor, and when the gas extraction volume per unit time is not more than 10 L/min, ending step (4).
    In some embodiments, the persulfate in the first component is ammonium persulfate; the porous carbon containing transition metal ions in the second component is porous carbon containing copper irons which is prepared by mixing copper sulfate and benzenetricarboxylic acid at a weight ratio of 6:4 in a ball mill and calcining the resulting mixture under a nitrogen atmosphere at 600 °C.
    In some embodiments, the first component is an aqueous solution of ammonium persulfate having a percent concentration by weight of 5%-10%; and the second component is a mixture of water and the porous carbon containing copper ions having a percent concentration by weight of 6%. The present invention has the following beneficial effects: In the present invention, during the hydraulic fracturing of coal seams, the hydraulic fracturing fluid and organic matter with different molecular weights in the coal seam continuously perform oxidation and in-situ modification reactions in a wide temperature range, thereby partially dissolving organic matters with a low molecular weight, dredging fractures and pores in the coal seam, and reducing the methane adsorbability of the coal seam. Therefore, compared with the simple hydraulic fracturing in the prior art, in the present invention, gas absorbed by the coal seam is converted to free gas, which greatly improves the permeability enhancement effect of the coal seam.
    The ultrasonic vibration plate promotes the uniform and thorough mixing of water and the porous carbon containing transition metal ions by transmitting ultrasonic waves to water, which improves the reaction efficiency between the hydraulic fracturing fluid and the organic matter in the coal seam.
    The gas extraction system in the present invention has a simple structure, is convenient for operation, and is capable of conveniently performing hydraulic fracturing in the coal seam using the hydraulic fracturing fluid. It is possible to enhance the permeability by employing water or only a persulfate solution as the hydraulic fracturing fluid, but it causes a poor effect. However, the permeability is obviously enhanced when the hydraulic fracturing fluid is obtained by mixing a solution of persulfate and a mixture of water and the porous carbon containing transition metal ions.
    Compared with existing gas extraction methods, the gas extraction method in the present invention uses the hydraulic fracturing fluid and the gas extraction system to greatly improve the gas extraction efficiency, which not only solves safety problems caused by coal seam gas, but also improves the gas extraction efficiency and the gas production.
    In conclusion, the hydraulic fracturing fluid, the gas extraction system and the gas extraction method in the present invention are safe, stable and high-efficient.
    BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows a gas extraction system according to an embodiment of the present invention.
    Fig. 2 schematically shows gas extraction rates of a single extraction borehole using different hydraulic fracturing solutions according to an embodiment of the present invention.
    DETAILED DESCRIPTION OF EMBODIMENTS The present invention provides a hydraulic fracturing fluid for fracturing and increasing permeability of a coal seam, which includes a first component and a second component, wherein the first component is an aqueous solution of persulfate;
    the second component is a mixture of water and porous carbon containing transition metal ions; and based on the hydraulic fracturing fluid, the first component is 0.9-1.1 parts by volume, and the second component is 0.9-1.1 parts by volume; preferably, based on the hydraulic fracturing fluid, the first component is 1 part by volume, and the second component is 1 part by volume.
    In some embodiments, the persulfate in the first component is ammonium persulfate and/or sodium persulfate and/or calcium persulfate and/or potassium persulfate, i.e., persulfate is one or combinations of ammonium persulfate, sodium persulfate, calcium persulfate and potassium persulfate; and the first component includes 1-25 parts by weight of persulfate and 100 parts by weight of water.
    The porous carbon containing transition metal ions in the second component is prepared by the following steps.
    Transition metal salt is mixed with aromatic carboxylic acid in a ball mill to obtain a mixture, and the mixture is calcined in an inert atmosphere at high temperature to obtain porous carbon containing transition metal ions; where the ball mill is a conventional device, so the specific structure thereof is not described herein.
    The transition metal salt is nickel nitrate and/or manganese chloride and/or cobalt nitrate and/or copper sulfate and/or zinc nitrate, i.e., the transition metal salt is one or combinations of nickel nitrate, manganese chloride, cobalt nitrate, copper sulfate and zinc nitrate; the aromatic carboxylic acid is benzenetricarboxylic acid and/or terephthalic acid and derivatives thereof and/or p-hydroxybenzoic acid and/or p-aminobenzoic acid, i.e., the aromatic carboxylic acid is one or combinations of benzenetricarboxylic acid, terephthalic acid and derivatives thereof, p- hydroxybenzoic acid and p-hydroxybenzoic acid; the inert atmosphere is nitrogen or argon, and a calcining temperature is 500-1000 °C; the transition metal salt is 0.8-
    1.2 parts by weight, preferably 1.2 parts, and the aromatic carboxylic acid is 0.8-1.2 parts by weight, preferably 0.8 part.
    The second component comprises not more than 25 parts by weight of porous carbon containing transition metal ions and 100 parts by weight of water.
    As shown in Fig. 1, the invention further discloses a gas extraction system using the hydraulic fracturing fluid, which includes a fracturing borehole 3 and a plurality of extraction boreholes 4 provided between a roof 1 and a floor 2 of the coal seam. The fracturing borehole 3 is provided with a fractured area, where the coal in the fractured area is fractured and permeability thereof is enhanced. The extraction boreholes 4 are provided in the fractured area at the left and right sides of the fracturing borehole 3, respectively.
    A fracturing pipe 5 is inserted in the fracturing borehole 3, and an extraction pipe 6 is inserted in each of the extraction boreholes 4. A fluid inlet is provided on the fracturing pipe 5, so that the fluid flows from the fracturing pipe 5 to the coal seam through the fracturing borehole 3; and a gas outlet is provided on the extraction pipe 6, so that the gas flows from the coal seam to the extraction pipe 6 through the extraction boreholes 4; it is a conventional technique to provide openings on pipes, so the inlet on the fracturing pipe 5 and the outlets on the extraction pipe 6 are not shown in the drawings.
    The fracturing pipe 5 extends out of the floor 2 of the coal seam and is connected to a mixer 7; the mixer 7 is provided with a first inlet 8, a second inlet 9 and an outlet 10; the outlet 10 of the mixer is connected to the fracturing pipe 5; the first inlet 8 of the mixer is connected to a first component feeder, and the second inlet 9 of the mixer is connected to a second component feeder.
    The fracturing pipe 5 between the mixer 7 and the fracturing borehole 3 is connected with a pressure gauge 11 and a discharge pipe 12 which is provided with a discharge valve 13.
    The extraction pipe 6 extends out of the floor 2 of the coal seam and is connected to a main extraction pipe 14; the main extraction pipe 14 is connected to a gas extractor 15 and provided with a main extraction valve 16, and an extraction valve 17 is provided on the extraction pipe 6.
    The gas extractor 15 is existing and is able to generate a negative pressure (containing a negative pressure generator such as an exhaust fan), which is not further described herein.
    In some embodiments, the first component feeder includes a first component feed tank 18 which is connected to a first component feed pump 20 via a first outlet pipe 19; an outlet of the first component feed pump 20 is connected to the first inlet 8 of the mixer 7 via a first component feed pipe 21, and a first component feed valve 22 is provided on the first component feed pipe 21; and the second component feeder includes a second component feed tank 23 which is connected to a second component feed pump 25 via a second outlet pipe 24; an outlet of the second component feed pump 25 is connected to the second inlet 9 of the mixer 7 via a second component feed pipe 26, and a second component feed valve 27 is provided on the second component feed pipe 26.
    The first component feed pump 20 and the second component feed pump 25 are the same type, so they have the same feed volume, which ensures that a volume ratio of the first component to the second component is approximately 1:1.
    The gas extraction system in the present invention has a simple structure, is convenient for operation, and is able to pump the mixture of the first and second components to the fracturing borehole 3, thereby fracturing the coal seams around the fracturing boreholes. The gas extractor 15 generates a negative pressure to extract the gas in the fractured area via the extraction boreholes 4, the extraction pipe 6 and the main extraction pipe 14. The hydraulic fracturing fluid in the invention is employed to achieve a complex operation of fracturing and extraction, which obviously improves the gas extraction efficiency compared with ordinary gas extraction systems.
    In some embodiments, an ultrasonic vibration plate 28 is provided on a bottom of the second component feed tank 23, and an ultrasonic generator is provided on the ultrasonic vibration plate 28. The ultrasonic generator is a conventional device and is not shown in the drawings.
    The ultrasonic vibration plate 28 promotes an even mixing of water and porous carbon containing transition metal ions by transmitting ultrasonic waves to water.
    The invention further discloses a gas extraction method using the gas extraction system, which includes the following steps.
    (1) Preparation
    (1.1) Boreholes are drilled and the hydraulic fracturing fluid is prepared.
    A fracturing borehole 3 and two extraction boreholes 4 are drilled by a drilling rig from the floor 2 to the roof 1 of the coal seam, and the two extraction boreholes 4 are located in the fractured area at two sides of the fracturing borehole 3, respectively.
    The hydraulic fracturing fluid is prepared by preparing the first component and the second component, respectively.
    Specifically, 1-25 parts by weight of persulfate is dissolved in 100 parts by weight of water to obtain the first component, and the first component is stored in the first component feed tank 18; transition metal salt is mixed with aromatic carboxylic acid to obtain a mixture, and the mixture is calcined in an inert atmosphere at high temperature to obtain porous carbon containing transition metal ions. The porous carbon containing transition metal ions is placed in water to obtain the second component, and the second component is stored in the second component feed tank
    23. The ultrasonic generator on the ultrasonic vibration plate 28 is turned on, so that the porous carbon containing transition metal ions evenly disperses in water in the second component feed tank 23.
    (1.2) Fracturing equipment and extraction equipment are arranged.
    The pressure gauge 11 and the discharge pipe 12 are pre-installed on a part of the fracturing pipe 5 out of the fracturing borehole 3, and the discharge valve 13 is pre-installed on the discharge pipe 12. The main extraction valve 16 is pre-installed on the main extraction pipe 14, and the extraction valve 17 is pre-installed on the extraction pipe 6.
    The arrangement of the fracturing equipment is described as follows. The fracturing pipe 5 is placed in the fracturing borehole 3, such that one end of the fracturing pipe 5 reaches the roof 1 of the coal seam, and the other end of the fracturing pipe 5, out of the fracturing borehole 3, is connected to the outlet 10 of the mixer 7.
    Individual parts of the first component feeder are connected, and the first component feed pipe 21 is connected to the first inlet 8 of the mixer 7.
    Individual parts of the second component feeder are connected, and the second component feed pipe 26 is connected to the second inlet 9 of the mixer 7.
    The arrangement of the extraction equipment is described as follows. The extraction pipe 6 is placed in each of the extraction boreholes 4, such that one end of the extraction pipe 6 reaches the roof 1 of the coal seam, and the other end of the extraction pipe 6, out of each of the extraction boreholes 4, is connected to the main extraction pipe 14; and the main extraction pipe 14 is connected to the gas extractor
    15. (2) Sealing boreholes The fracturing borehole 3 and the extraction boreholes 4 are sealed by a hole packer.
    (3) Hydraulic fracturing The discharge valve 13 is closed. The first component feed valve 22, the second component feed valve 27, the first component feed pump 20 and the second component feed pump 25 are opened. The first and the second components are pumped to the fracturing borehole 3 at the same time to fracture the coal seam to increase the permeability thereof.
    An initial pressure in the fracturing pipe 5 is recorded within 5 min by reading the pressure gauge 11 after the first component feed pump 20 and the second component feed pump 25 are turned on, where the initial pressure is 25-30 MPa.
    The pressure gauge 11 is continuously observed; when a pressure in the fracturing pipe drops to 1513 MPa and remains not more than 18 MPa for 5 min, the first component feed valve 22, the second component feed valve 27, the first component feed pump 20 and the second component feed pump 25 are closed; and the discharge valve 13 is opened to release the pressure in the fracturing pipe 5; when the pressure reading on the pressure gauge 11 returns to the atmospheric pressure, the discharge valve 13 is closed.
    (4) Gas extraction The main extraction valve 16 and extraction valves 17 are opened, the gas extractor 15 is started to extract gas in the extraction boreholes 4 and the gas is stored.
    A gas extraction volume per unit time is observed via the gas extractor 15. When the gas extraction volume per unit time is not more than 10 L/min, step (4) is ended.
    In some embodiments, the persulfate in the first component is ammonium persulfate.
    In some embodiments, porous carbon containing transition metal ions in the second component is porous carbon containing copper irons. Copper sulfate and benzenetricarboxylic acid are mixed at a weight ratio of 6:4 in a ball mill and the resulting mixture is calcined under a nitrogen atmosphere at 600 °C to obtain the porous carbon containing copper ions.
    In some embodiments, the first component is an aqueous solution of ammonium persulfate having a percent concentration by weight of 2%-10%; preferably 5%-10%; and the second component is a mixture of water and the porous carbon containing copper ions having a percent concentration by weight of 1%-6%, preferably 6%. The present invention provides the hydraulic fracturing fluid, the gas extraction method and the gas extraction system, such that organic matter with low molecular weight is dissolved, fractures and pores in the coal seam are enlarged, increased and dredged, resulting in a smoother channel for gas extraction to improve the gas extraction efficiency. Moreover, the aromatic flakes in the coal are oxidized in-situ, and the methane adsorbability of the coal seam is reduced, so that the adsorbed gas is transferred to free gas, providing gas supply for the continuous and high-efficient gas extraction.
    Experiments for hydraulic fracturing and gas extraction respectively using only water and the hydraulic fracturing fluid in the present invention were carried out herein. The first component was an aqueous solution of ammonium persulfate.
    Experiments for hydraulic fracturing and gas extraction using the first component with different weight concentrations of ammonium persulfate were carried out and the results thereof were shown in Fig. 2. In Fig. 2, group A represented that only water was used for the hydraulic fracturing and gas extraction; group B represented that the first component was an aqueous solution of 2% by weight of ammonium persulfate; group C represented that the first component was an aqueous solution of
    5% by weight of ammonium persulfate; group D represented that the first component was an aqueous solution of 10% by weight of ammonium persulfate; group E represented that the first component was an aqueous solution of 2% by weight of ammonium persulfate and simultaneously the second component was a mixture of water and 1% by weight of porous carbon containing copper ions; group F represented that the first component was an aqueous solution of 5% by weight of ammonium persulfate and simultaneously the second component was a mixture of water and 2% by weight of porous carbon containing copper ions; and group G represented that the first component was an aqueous solution of 10% by weight of ammonium persulfate and simultaneously the second component was a mixture of water and 6% by weight of porous carbon containing copper ions.
    It was concluded from Fig. 2 that group G had the optimal extraction effect, that is, when the first component was an aqueous solution of 10% by weight of ammonium persulfate and simultaneously the second component was a mixture of water and 6% by weight of porous carbon containing copper ions, the gas extraction rate was 95 L/min. Compared with group G, group F had a lower gas extraction rate, but the gas extraction rate thereof is 78 L/min, which was still tar higher than other groups. Moreover, group F only used half of ammonium persulfate and two thirds of porous carbon of group G, resulting in lower cost. Therefore, in the present invention, the optimal dosage range of ammonium persulfate is between dosages of ammonium persulfate in groups G and F, i.e., 5%-10%.
    It was also seen from Fig. 2 that as long as the hydraulic fracturing fluid in the present invention was employed, the gas extraction rate was increased. When the permeability of the coal seam was enhanced by adopting an aqueous solution of persulfate to corrode and modify the coal in the coal reservoirs during the hydraulic fracturing, average gas extraction rate of every borehole was increased obviously, and the permeability enhancement effect was greatly improved. The permeability enhancement effect was poor when only water or the aqueous solution of persulfate is used as the hydraulic fracturing fluid, and the permeability enhancement effect was greatly improved by using a mixed solution of persulfate and porous carbon containing copper ions.
    There are differences between the present invention and the methods using acids for permeability enhancement. Hydrochloric acid, hydrofluoric acid and acetic acid dissolve carbonate minerals and sulfides in coal. Although the number of pores in the coal can be increased, it is not effective to enhance the connectivity of the pores and fractures. The hydraulic fracturing fluid of the invention can dissolve organic matters with low molecular weights in the coal, which not only increases the number of pores in the coal, but also greatly improves the connectivity of pores and fractures in the coal, thereby providing more favorable conditions for gas extraction.
    There are differences between the present invention and methods using chlorine dioxide for permeability enhancement. Chlorine dioxide has strong oxidizing properties, but is extremely unstable and highly chemically corrosive. In addition, it is very sensitive to heat, vibration, impact and friction, easy to decompose to cause explosions, and inconvenient to be transported. Only on-site preparation is reliable, and it is difficult for on-site application on a large scale. However, respective components of the hydraulic fracturing fluid in the present invention are safe and stable during the whole process of transportation, storage and use.
    There are differences between the present invention and the methods using Fenton reagent (a strong oxidation system containing hydrogen peroxide and ferrous ions) for permeability enhancement. Hydrogen peroxide decomposes quickly, especially at high concentrations, so that the Fenton reagent has strong oxidizing properties only in the first few minutes after preparation, so it is difficult to store, and must be prepared on site, and works only within few minutes after entering the coal seam. However, the hydraulic fracturing fluid of the present invention does not need to be prepared on site, and can continuously react with organic matters in the coal seam after entering the coal seam.
    The above-mentioned embodiments are merely an illustration of the invention and are not intended to limit the scope of the invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood that any modifications or equivalent replacements obtained by those skilled in the art without departing from the spirit of the invention shall fall within the scope of the appended claims.
    权利要求:
    Claims (10)
    [1]
    A hydraulic cracking fluid, characterized in that the hydraulic cracking fluid is adapted to crack and increase the permeability of a coal seam, comprising a first component and a second component; wherein the first component is an aqueous solution of persulfate; the second component is a mixture of water and porous carbon comprising transition metal ions; and based on the hydraulic cracking fluid, the first component is 0.9-1.1 by volume and the second component is 0.9-1.1 by volume.
    [2]
    The hydraulic cracking fluid according to claim 1, characterized in that based on the hydraulic cracking fluid, the first component is 1 part by volume and the second component is 1 part by volume.
    [3]
    The hydraulic cracking fluid according to claim 1, characterized in that the persulfate in the first component is an ammonium persulfate and / or a sodium persulfate and / or calcium persulfate and / or potassium persulfate; and the first component comprises 1-25 parts by weight persulfate and 100 parts by weight water.
    [4]
    The hydraulic cracking fluid according to any one of claims 1 to 3, characterized in that the porous carbon comprising transition metal ions in the second component are prepared by a method comprising the steps of; mixing transition metal salt with aromatic carboxylic acid in a ball mill to obtain a mixture; and calcining the mixture in an inert atmosphere at a high temperature to obtain the porous carbon comprising transition metal ions; wherein the transition metal salt is nickel nitrate and / or manganese chloride and / or cobalt nitrate and / or copper sulfate and / or zinc nitrate; the aromatic carboxylic acid is a benzenecarboxylic acid and / or terephthalic acid and derivatives thereof and / or p-hydroxybenzoic acid and / or p-aminobenzoic acid; the inert atmosphere is nitrogen or argon, and a calcination temperature is 500-1000 degrees Celsius; the transition metal salt is 0.8-1.2 parts by weight, and the aromatic carboxylic acid is
    0.8-1.2 parts by weight; and the second component comprises 25 parts or less by weight of the porous carbon comprising transition metal ions and 100 parts by weight of water.
    [5]
    A gas extraction system using the hydraulic cracking fluid of claim 4, comprising a cracking wellbore and a plurality of extraction wells disposed between a roof and a bottom of the coal seam; characterized in that the cracking borehole has a cracking area in the coal seam, and the extraction boreholes are respectively provided in the cracking area on the left and right side of the cracking borehole; A crack pipe is inserted into the crack borehole, and an extraction pipe is inserted into each of the extraction boreholes; the crack pipe is provided with a liquid inlet, and the extraction pipe is provided with a gas outlet; the squat pipe extends down through the bottom of the coal seam and is connected to a mixer; the mixer has a first inlet, a second inlet and an outlet, the outlet of the mixer is connected to the crack pipe, the first inlet of the mixer is connected to a first component supply, and the second inlet of the mixer is connected to a second component supply; the crack pipe between the mixer and the crack borehole is connected to a pressure gauge and a discharge pipe provided with a discharge valve; and the extraction pipe extends down through the bottom of the coal seam and is connected to a main extraction pipe which is connected to a gas extractor and has a main extraction valve, and the extraction pipe is provided with an extraction valve.
    [6]
    The gas extraction system of claim 5, characterized in that the first component supply comprises a first component supply tank connected via a first exhaust pipe to a first component supply pump; an outlet of the first component supply pump is connected to the first inlet of the mixer through a first component supply pipe, and the first component supply pipe has a first component supply valve; and The second component supply includes a second component supply tank connected through a second exhaust pipe to a second component supply pump; an outlet of the second component supply pump is connected to the second inlet of the mixer through a second component supply pipe, and the second component supply pipe has a second component supply valve.
    [7]
    The gas extraction system according to claim 6, characterized in that a bottom of the second component supply tank is provided with an ultrasonic vibrating plate and the ultrasonic vibrating plate is provided with an ultrasonic generator.
    [8]
    A gas extraction method using the gas extraction system according to claim 7, comprising: (1) preparing (1.1) drilling and preparing the hydraulic fracturing fluid drilling one crack borehole and two extraction boreholes at a drilling platform from the bottom to the roof of a coal seam, such that the two extraction wells are respectively in the cracking area on two sides of the cracking well; preparing the first component: dissolving 1-25 parts by weight of persulfate in 100 parts by weight of water to obtain the first component and storing the first component in the first component supply tank; and preparing the second component: mixing the transition metal salt with aromatic carboxylic acid to obtain a mixture, calcining the mixture in an inert atmosphere at a high temperature to obtain the porous carbon containing transition metal ions; placing the porous carbon comprising transition metal ions in water to obtain the second component and storing the second component in the second component supply tank; and turning on the ultrasonic generator on the ultrasonic vibrating plate so that the porous carbon comprising transition metal ions are evenly dispersed in the water in the second component supply tank; (1.2) controlling cracking equipment and extraction equipment pre-installing the pressure gauge and the discharge pipe on a part of the cracking pipe outside the cracking borehole, and installing the discharge hopper on the discharge pipe in advance; and pre-installing the main extraction valve on the main extraction pipe, and pre-installing the extraction valve on the extraction pipe;
    placing the crack pipe in the cracking borehole so that one end of the cracking pipe reaches the roof of the coal seam, and the other end of the crack pipe, outside of the cracking borehole, is connected to the outlet of the mixer; connecting the separate parts of the first component supply and connecting the first component supply pipe to the first inlet of the mixer; connecting the separate parts of the second component supply and connecting the second component supply pipe to the second inlet of the mixer; and controlling the extraction equipment: placing the extraction pipe in each of the extraction boreholes so that one end of the extraction pipe reaches the roof of the coal seam, and the other end of the extraction pipe, outside each of the extraction boreholes, is connected to the main extraction pipe; connecting the main extraction pipe to the gas extractor; (2) hole sealing sealing openings of the cracking and extraction boreholes by a sealing device (3) hydraulic cracking; Close the discharge valve; opening the first and second component supply valves and the first and second component supply pumps; simultaneously pumping the first and second components to the cracking borehole to crack the coal seam to increase the permeability thereof; registering an initial pressure in the crack pipe by reading the pressure gauge within 5 minutes after the first and second component supply pumps are turned on, the initial pressure being 25-30 MPa; continuously observing the pressure gauge; when a pressure in the cracking line falls to 15 3 MPa and does not exceed 18 MPa for 5 minutes, closing the first and second component supply valves, and the first and second component supply pumps; and opening the discharge valve to relieve the pressure in the crack pipe; when the pressure reading on the pressure gauge returns to atmospheric pressure, the discharge valve closes; and (4) gas extraction opening the main extraction valve and extraction valves, starting the gas extractor to extract gas in the extraction wells and store the gas;
    observing a gas extraction volume per unit time via the gas extractor, and when the gas extraction volume per unit time is not more than 10 µl / min, terminating step (4).
    [9]
    9. the gas extraction method according to conicus 8, characterized in that the persulfate in the first component is an ammonium persulfate; the porous carbon comprising transition metal ions in the second component are porous carbon comprising copper irons, which is prepared by mixing copper sulfate and benzene carboxylic acid in a weight ratio of 6: 4 in a ball mill and calcining the resulting mixture in a nitrogen atmosphere at 600 degrees Celsius.
    [10]
    The gas extraction process according to claim 9, characterized in that the first component is an aqueous solution of ammonium persulfate with a mass percentage of 5% -10%; and the second component is a mixture of water and porous carbon comprising copper ions at a weight percentage of 6%.
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    引用文献:
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    US5964290A|1996-01-31|1999-10-12|Vastar Resources, Inc.|Chemically induced stimulation of cleat formation in a subterranean coal formation|
    CN110656973B|2019-11-08|2021-05-18|湖南科技大学|Method for preventing and treating mine gas emission|
    CN111075496B|2020-03-09|2021-04-02|河南理工大学|Device for comprehensively eliminating and suppressing outburst and dust of coal bed by injecting flue gas absorption liquid at low pressure and outburst-eliminating and dust-suppressing method|
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    申请号 | 申请日 | 专利标题
    CN201910621623.3A|CN110259427A|2019-07-10|2019-07-10|Hydrofrac fluid, gas drainage system and gas pumping method|
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