A temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes

Abstract

The present invention relates to a temporary plugging and fracturing method for medium- and high-rank coalbed methane reservoirs based on plant enzymes, comprising S101: preparing a fracturing fluid; S102: implementing hydraulic fracturing; S103: transforming coalbed fractures by means of the fracturing fluid; and S104: injecting an acidic solution. Due to the adoption of the above technical scheme, the temporary plugging and fracturing method for medium- and high-rank coalbed methane reservoirs based on plant enzymes of the present invention can promote the fracturing of coal reservoirs to form highly conductive and highly permeable fractures that can be expanded over a large range, thereby improving fracture permeability, gas extraction purity, and gas extraction speed.

Description

Technical Field

[0001] The invention relates to the technical field of coalbed methane exploitation, and in particular to a temporary plugging and fracturing method for medium- and high-rank coalbed methane reservoirs based on plant enzymes. Background Art

[0002] my country is rich in coalbed methane resources. The geological resources of shallow coalbed methane within a burial depth of less than 2,000 meters are about 36 trillion cubic meters, with huge development potential. At present, my country's coalbed methane exploration and development are mainly concentrated in medium and high-rank coal seams represented by the Qinshui Basin and the eastern edge of the Ordos Basin. The coalification degree of medium and high-rank coal gas reservoirs is relatively high, and there are a large number of primary fractures inside them. When hydraulic fracturing is carried out to increase permeability, most of the fracturing fractures are extensions and penetrations of the primary fractures in the reservoir. Relevant scholars and on-site fracturing construction have found that due to the mutual interference between primary fractures, the expansion of fracturing fractures is very complicated and difficult to expand on a large scale. At the same time, because primary fractures are often very rough and tortuous, the diversion and permeability of fracturing fractures are very limited. Therefore, how to form high-conductivity and high-permeability fracturing fractures that can be expanded over a large range is the key to effectively improve the fracturing transformation effect and permeability of fracture-type coalbed methane reservoirs. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes to solve the technical problem of how to form high-conductivity and high-permeability fracturing cracks that can be expanded over a large range.

[0004] The present invention is achieved through the following technical solutions:

[0005] A temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes, comprising the following steps:

[0006] S101: preparing a fracturing fluid, wherein the fracturing fluid comprises a plant extract having a plant enzyme activity of 5 to 8 mmol / min, a mixed solution of amide nitrogen fertilizer and calcium salt at a concentration ratio of 1.5:1, a lignin sulfonate solution having a concentration of 20 to 22 g / L, and a skim milk powder solution having a concentration of 5 to 10 g / L; the concentration of the amide nitrogen fertilizer is 0.75 to 1.05 mol / L, and the concentration of the calcium salt solution is 0.5 to 0.7 mol / L;

[0007] S102: Perform hydraulic fracturing, inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam;

[0008] S103: Reconstructing coal seam fractures by using the fracturing fluid, and repeatedly injecting the fracturing fluid described in step S101 into the coal seam for multiple times, wherein the fracturing fluid generates calcium carbonate precipitates with cementing properties under the mineralization effect to seal artificial fractures and primary fractures in the coal seam, and press out new fractures in the coal seam;

[0009] S104: injecting an acid solution into the coal seam to acidify the original fractures and the artificial fractures formed, and dissolving the calcium carbonate in the original fractures and the artificial fractures.

[0010] Furthermore, after performing step S104, a carbon dioxide aqueous solution with a concentration of 0.02-0.04 mol / L and a temperature of 2-10 degrees is injected into the coal seam under normal temperature conditions, the injection pressure is 5-10 MPa, and the construction displacement is 100L / min-200L / min.

[0011] Furthermore, the method for preparing the plant extract in step S101 comprises the following steps:

[0012] S1011: at 4° C., crushing the plant and passing the crushed plant through a 80-120 mesh sieve;

[0013] S1012: adding the plants sieved out from the mesh of the sieve in step S1011 to carboxylesterase at a temperature of 4° C. and a concentration of 0.1 to 0.5 mg / ml or Tris-CH3COOH buffer at a temperature of 4° C. and a concentration of 2.5% to 3% at a solid-liquid ratio of 1:10, and shaking well for 25 to 30 minutes to form a mixed solution;

[0014] S1013: Soak the mixed solution obtained in step S1012 in a 4° C. refrigerator for 24 hours;

[0015] S1014: the mixed solution after immersion in step S1013 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected;

[0016] S1015: adding the residue remaining after collecting the supernatant in step S1014 to a carboxylesterase having a temperature of 4° C. and a concentration of 0.1 to 0.5 mg / ml or a Tris-CH3COOH buffer having a temperature of 4° C. and a concentration of 2.5% to 3% at a solid-liquid ratio of 1:10, and shaking well for 25 to 30 minutes to form a mixed solution;

[0017] S1016: Soak the mixed solution obtained in step S1015 in a 4° C. refrigerator for 24 hours;

[0018] S1017: the mixed solution after soaking in step S1016 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected;

[0019] S1018: Mix the supernatant obtained in step S1014 and the supernatant obtained in step S1017 and filter them with 25-30 mm thick glass wool.

[0020] Furthermore, the plant is soybean, pumpkin seed, watermelon seed, green bean, asparagus or spinach.

[0021] Furthermore, the calcium salt in step S101 is one of calcium bromide, calcium iodide, calcium nitrate and calcium chloride, or a mixture of several thereof.

[0022] Furthermore, the lignin sulfonate in step S101 is sodium lignin sulfonate, calcium lignin sulfonate or potassium lignin sulfonate.

[0023] Furthermore, the value of the expansion pressure P required to be provided to the coal seam in step S102 is z According to formula 1:

[0024]

[0025] Calculation shows that, in the above formula: E is the elastic modulus of the coal body; γ is the surface energy per unit area; υ is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is the empirical coefficient, generally taken as 1.05~1.15.

[0026] Furthermore, the duration T of injecting active water into the coal seam in step S102 is based on Formula 2:

[0027]

[0028] Calculation shows that, in the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the water injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

[0029] Furthermore, the device for injecting fracturing fluid into the coal seam in the step S103 includes a tee joint, a first grouting pipe connected to the tee joint at one end, a first high-pressure pump connected to the other end of the first grouting pipe, a second grouting pipe connected to the tee joint at one end, a second high-pressure pump connected to the other end of the second grouting pipe, and a third grouting pipe connected to the tee joint at one end and inserted into the coal seam at the other end; when injecting fracturing fluid into the coal seam in the step S103, the first high-pressure pump injects a mixed solution of lignin sulfonate solution, plant extract, and skimmed milk powder solution in a volume ratio of 1:2:1 into the third grouting pipe at a flow rate of Q1=7~13L / min through the first grouting pipe; at the same time, the second high-pressure pump injects a mixed solution of amide nitrogen fertilizer and calcium salt into the third grouting pipe at a flow rate of 3Q1 through the second grouting pipe.

[0030] Furthermore, the acidic solution in step S104 is CH3COOH with a concentration of 15%, and the flow rate of CH3COOH injected into the coal seam is 50 L / min.

[0031] The beneficial effects of the present invention include:

[0032] Plant enzymes, calcium ion sources, sodium lignin sulfonate, skimmed milk powder and amide nitrogen fertilizer generate calcium carbonate precipitation with cementing properties under mineralization, which can temporarily block artificial cracks and native cracks in coal seams, promote coal reservoir fracturing to form artificial cracks with high conductivity and high permeability that can be expanded over a large range, and the newly generated artificial cracks are straighter and smoother than the native cracks in the coal seams, and have strong conductivity and permeability, thereby improving the crack permeability, gas extraction quantity and gas extraction speed. Skimmed milk powder allows calcium carbonate crystals in the environment to quickly aggregate and deposit; sodium lignin sulfonate can quickly attract calcium ions in the surrounding environment, provide crystal nuclei for the generated calcium carbonate crystals, and provide the required alkaline environment for mineralization, accelerating the speed of calcium carbonate crystallization and mineralization. After fracturing is completed, the generated calcium carbonate is dissolved with an acidic solution, and the native cracks in the coal body will not be permanently blocked. The fracturing fluid prepared in the temporary plugging and fracturing method for medium and high-order coalbed methane reservoirs based on plant enzymes described in the present invention has the advantages of being environmentally friendly and having little pollution to the formation.

[0033] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the process diagram of the present invention;

[0035] Figure 2 It is a schematic structural diagram of a device for injecting fracturing fluid into a coal seam in the present invention;

[0036] Figure 3 It is a permeability comparison chart;

[0037] Figure 4 This is a comparison chart of gas content;

[0038] Figure 5 This is a comparison chart of the average pure amount of gas extracted from a single borehole;

[0039] Figure 6 This is a comparison chart of extraction speed;

[0040] The meanings of the numbers in the accompanying drawings are as follows:

[0041] Tee joint-1; first grouting pipe-2; first high-liquid pump-3; second grouting pipe-4; second high-pressure pump-5; third grouting pipe-6; rock layer-7; coal layer-8. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0045] In the above description of the present invention, it should be noted that the terms "one side", "the other side", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0046] In addition, the term "same" does not mean that the parts must be absolutely the same, but slight differences are allowed. The term "vertical" only means that the positional relationship between the parts is more vertical than "parallel", and does not mean that the structure must be completely vertical, but can be slightly tilted.

[0047] See also Figure 1 The present invention provides a technical solution: a temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes, comprising the following steps:

[0048] S101: preparing a fracturing fluid, wherein the fracturing fluid comprises a plant extract having a plant enzyme activity of 5 to 8 mmol / min, a mixed solution of amide nitrogen fertilizer and calcium salt at a concentration ratio of 1.5:1, a lignin sulfonate solution at a concentration of 20 to 22 g / L, and a skimmed milk powder solution at a concentration of 5 to 10 g / L; the concentration of the amide nitrogen fertilizer is 0.75 to 1.05 mol / L, and the concentration of the calcium salt solution is 0.5 to 0.7 mol / L; and the plant enzyme is a protease that can accelerate the hydrolysis of amide nitrogen fertilizer (i.e., urea).

[0049] The method for preparing the plant extract in step S101 comprises the following steps:

[0050] S1011: at 4° C., crush the plant and pass the crushed plant through a 80-120 mesh sieve; the plant may be soybean, pumpkin seed, watermelon seed, green bean, asparagus or spinach. The sieve is a stainless steel sieve, and it is understood that in other embodiments, the sieve may also be made of other materials.

[0051] S1012: Add the plants sieved out from the sieve holes of the sieve in step S1011 into carboxylesterase at a temperature of 4°C and a concentration of 0.1-0.5 mg / ml or into Tris-CH3COOH buffer at a temperature of 4°C and a concentration of 2.5%-3% at a solid-liquid ratio of 1:10, and shake well for 25-30 minutes to form a mixed solution.

[0052] S1013: Soak the mixed solution obtained in step S1012 in a 4°C refrigerator for 24 hours.

[0053] S1014: The mixed solution after immersion in step S1013 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected.

[0054] S1015: Add the filter residue remaining after collecting the supernatant in step S1014 to a carboxylesterase at a temperature of 4°C and a concentration of 0.1-0.5 mg / ml or a Tris-CH3COOH buffer at a temperature of 4°C and a concentration of 2.5%-3% at a solid-liquid ratio of 1:10, and shake well for 25-30 minutes to form a mixed solution.

[0055] S1016: Soak the mixed solution obtained in step S1015 in a 4°C refrigerator for 24 hours.

[0056] S1017: The mixed solution after soaking in step S1016 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected.

[0057] S1018: Mix the supernatant obtained in step S1014 and the supernatant obtained in step S1017 and filter them with 25-30 mm thick glass wool.

[0058] According to the above steps S1011-S1018, a plant extract can be prepared, the plant extract is mixed with 1 mol / L amide nitrogen fertilizer at a volume ratio of 1:9, and then the activity of the plant enzyme in the plant extract is detected. If the activity of the plant enzyme in the plant extract is within the range of 5-8 mmol / min, the plant extract is qualified. The qualified plant extract is placed in a refrigerator and stored at 4°C for use.

[0059] In this step, the calcium salt is one or a mixture of calcium bromide, calcium iodide, calcium nitrate and calcium chloride. That is, the calcium salt is one or a mixture of calcium bromide, calcium iodide, calcium nitrate and calcium chloride.

[0060] In this step, the lignin sulfonate is sodium lignin sulfonate, calcium lignin sulfonate or potassium lignin sulfonate.

[0061] S102: Implement hydraulic fracturing to inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam.

[0062] The value of the expansion pressure P required to be provided to the coal seam in this step z According to formula 1:

[0063]

[0064] Calculation shows that, in the above formula: E is the elastic modulus of the coal body; γ is the surface energy per unit area; υ is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is the empirical coefficient, generally taken as 1.05~1.15.

[0065] The duration T of injecting active water into the coal seam in this step is based on Formula 2:

[0066]

[0067] Calculation shows that, in the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the water injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

[0068] S103: The fracturing fluid is used to transform the coal seam fractures. The fracturing fluid described in step S101 is repeatedly injected into the coal seam. The fracturing fluid generates calcium carbonate precipitates with cementing properties under the mineralization effect to seal the artificial fractures and primary fractures in the coal seam, and press out new fractures in the coal seam.

[0069] See also Figure 2 In this step, the device for injecting fracturing fluid into the coal seam includes a three-way joint 1, a first grouting pipe 2 connected to the three-way joint 1 at one end, a first high-pressure pump 3 connected to the other end of the first grouting pipe 2, a second grouting pipe 4 connected to the three-way joint 1 at one end, a second high-pressure pump 5 connected to the other end of the second grouting pipe 4, and a third grouting pipe 6 connected to the three-way joint 1 at one end and inserted into the coal seam 8 at the other end, the upper end of the third grouting pipe 6 is connected to the three-way joint 1, and the lower end of the third grouting pipe 6 passes through the rock layer 7 and is located in the coal seam 8. When injecting fracturing fluid into the coal seam 8, the first high-pressure pump 3 injects a mixed solution of lignin sulfonate solution, plant extract and skimmed milk powder solution in a volume ratio of 1:2:1 into the third grouting pipe 6 through the first grouting pipe 2; at the same time, the second high-pressure pump 5 injects a mixed solution of amide nitrogen fertilizer and calcium salt into the third grouting pipe 6 through the second grouting pipe 4. The mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt are mixed in the third grouting pipe 6 and then injected into the coal seam 8. The calcium carbonate precipitate generated by the mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt temporarily blocks the artificial cracks and primary cracks in the coal seam 8, and further promotes the fracturing of the coal seam to expand the extension range of the cracks. Compared with the method of directly mixing the mixture of lignin sulfonate solution, plant extract and skim milk powder solution with the mixture of amide nitrogen fertilizer and calcium salt and then injecting them into the coal seam 8 through a pipeline, it can avoid the premature deposition of calcium carbonate at the injection port and causing pipeline blockage.

[0070] S104: injecting an acidic solution into the coal seam to acidify the original fractures and the artificial fractures formed, and dissolve the calcium carbonate in the original fractures and the artificial fractures. The carbon dioxide generated during the acidification of the coal seam can further resolve and replace the methane (i.e., gas) in the coal seam, increase the gas content, and inertate the fire zone. The acidic solution can be acetic acid, hydrochloric acid, or nitric acid.

[0071] In this step, the acid solution is CH3COOH with a concentration of 15%, and the flow rate of CH3COOH injected into the coal seam is 50L / min.

[0072] Plant enzymes, calcium ion sources, sodium lignin sulfonate, skimmed milk powder and amide nitrogen fertilizer generate calcium carbonate precipitation with cementing properties under mineralization, which can temporarily block artificial cracks and native cracks in coal seams, promote coal reservoir fracturing to form artificial cracks with high conductivity and high permeability that can be expanded over a large range, and the newly generated artificial cracks are straighter and smoother than the native cracks in the coal seams, and have strong conductivity and permeability, thereby improving the crack permeability, gas extraction quantity and gas extraction speed. Skimmed milk powder allows calcium carbonate crystals in the environment to quickly aggregate and deposit; sodium lignin sulfonate can quickly attract calcium ions in the surrounding environment, provide crystal nuclei for the generated calcium carbonate crystals, and provide the required alkaline environment for mineralization, accelerating the speed of calcium carbonate crystallization and mineralization. After fracturing is completed, the generated calcium carbonate is dissolved with an acidic solution, and the native cracks in the coal body will not be permanently blocked. The fracturing fluid prepared in the temporary plugging and fracturing method for medium and high-order coalbed methane reservoirs based on plant enzymes described in the present invention has the advantages of being environmentally friendly and having little pollution to the formation.

[0073] Step S105: After the step S104, a carbon dioxide aqueous solution with a concentration of 0.02-0.04 mol / L and a temperature of 2-10 degrees is injected into the coal seam at room temperature, with an injection pressure of 5-10 MPa and a construction displacement of 100L / min-200L / min. Carbon dioxide is used to further desorb and replace methane (i.e. gas) in the coal seam.

[0074] Embodiment 1

[0075] Temporary plugging and fracturing of medium and high-rank coalbed methane reservoirs are carried out through the following steps:

[0076] S101: preparing a fracturing fluid, wherein the fracturing fluid comprises a soybean extract having a plant enzyme activity of 8 mmol / min, a mixed solution of amide nitrogen fertilizer and calcium chloride at a concentration ratio of 1.5:1, a sodium lignin sulfonate solution having a concentration of 22 g / L, and a skimmed milk powder solution having a concentration of 10 g / L; the concentration of the amide nitrogen fertilizer is 1.05 mol / L, and the concentration of the calcium salt solution is 0.7 mol / L.

[0077] The method for preparing the plant extract in step S101 comprises the following steps:

[0078] S1011: Under 4°C, select 50 kg of fresh and clean soybeans, crush them, and pass the crushed soybeans through a 120-mesh stainless steel sieve.

[0079] S1012: Add the plants sieved out from the mesh of the stainless steel sieve in step S1011 into a Tris-CH3COOH buffer solution at a temperature of 4°C and a concentration of 3% at a solid-liquid ratio of 1:10, and shake well for 30 minutes to form a mixed solution.

[0080] S1013: Soak the mixed solution obtained in step S1012 in a 4°C refrigerator for 24 hours.

[0081] S1014: The mixed solution after immersion in step S1013 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 1000 rpm / min, homogenized for 2 minutes, allowed to stand for 3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 4000 rpm / min, and then the supernatant is collected.

[0082] S1015: Add the filter residue remaining after collecting the supernatant in step S1014 into a 3% Tris-CH3COOH (PH=7) buffer solution at a solid-liquid ratio of 1:10 at a temperature of 4°C and a concentration of 3%, and shake well for 30 minutes to form a mixed solution.

[0083] S1016: Soak the mixed solution obtained in step S1015 in a 4°C refrigerator for 24 hours.

[0084] S1017: The mixed solution after soaking in step S1016 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 1000 rpm / min, homogenized for 2 minutes, allowed to stand for 3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 4000 rpm / min, and then the supernatant is collected.

[0085] S1018: The supernatant obtained in step S1014 and the supernatant obtained in step S1017 are mixed and filtered through 30 mm thick glass wool.

[0086] According to the above steps S1011-S1018, a soybean extract can be obtained, the plant extract is mixed with 1 mol / L amide nitrogen fertilizer at a volume ratio of 1:9, and then the activity of the plant enzyme in the plant extract is detected. If the activity of the plant enzyme in the plant extract is within the range of 5-8 mmol / min, the plant extract is qualified. The qualified plant extract is placed in a refrigerator and stored at 4°C for use.

[0087] S102: Implement hydraulic fracturing, inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam.

[0088] According to formula 1:

[0089]

[0090] Calculate the expansion pressure P required to provide to the coal seam z It is 32MPa, where: E is the elastic modulus of the coal body; γ is the surface energy per unit area; υ is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is an empirical coefficient, generally taken as 1.05~1.15.

[0091] According to formula 2:

[0092]

[0093] Calculation shows that the duration T of injecting active water into the coal seam is 145 minutes. In the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

[0094] Through testing and fracturing analysis, the changing characteristics of crack extension under different displacements were obtained, and the optimal crack width was determined to be 300L / min, which is the optimal construction displacement.

[0095] S103: The fracturing fluid is used to transform the coal seam cracks. The fracturing fluid described in step S101 is repeatedly injected into the coal seam. The fracturing fluid generates calcium carbonate precipitates with cementing properties under the mineralization effect to seal artificial cracks and native cracks in the coal seam, and press out new cracks in the coal seam. The carbon dioxide generated during the acidification treatment of the coal seam can be further analyzed to replace the methane (i.e., gas) in the coal seam, thereby increasing the gas content and inerting the fire zone.

[0096] In this step, the device for injecting fracturing fluid into the coal seam includes a three-way joint, a first grouting pipe connected to the three-way joint at one end, a first high-pressure pump connected to the other end of the first grouting pipe, a second grouting pipe connected to the three-way joint at one end, a second high-pressure pump connected to the other end of the second grouting pipe, and a third grouting pipe connected to the three-way joint at one end and inserted into the coal seam at the other end, the upper end of the third grouting pipe is connected to the three-way joint, and the lower end of the third grouting pipe is located in the coal seam after passing through the rock layer. When injecting fracturing fluid into the coal seam, the first high-pressure pump injects a mixed solution of lignin sulfonate solution, plant extract and skimmed milk powder solution in a volume ratio of 1:2:1 into the third grouting pipe at a flow rate of Q1=7L / min through the first grouting pipe; at the same time, the second high-pressure pump injects a mixed solution of amide nitrogen fertilizer and calcium salt into the third grouting pipe at a flow rate of Q1=21L / min through the second grouting pipe. The mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt are mixed in the third grouting pipe and then injected into the coal seam. The calcium carbonate precipitation generated by the mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt temporarily blocks the artificial cracks and primary cracks in the coal seam, and further promotes the fracturing of the coal seam to expand the extension range of the cracks. Compared with the method of directly mixing the mixture of lignin sulfonate solution, plant extract and skim milk powder solution with the mixture of amide nitrogen fertilizer and calcium salt and injecting them into the coal seam through a pipeline, it can avoid the premature deposition of calcium carbonate at the injection port and causing pipeline blockage.

[0097] Each injection of fracturing fluid into the coal seam lasts for 12 hours. The time interval from the end of one injection of fracturing fluid into the coal seam to the start of the next injection of fracturing fluid into the coal seam is 12 hours. After four injections of fracturing fluid into the coal seam, the length of the main crack reached 200m and the width reached 450mm.

[0098] S104: Inject acid solution into the coal seam for 10m 3 The concentration of CH3COOH is 15%, and the flow rate of CH3COOH injected into the coal seam is 50L / min. The original fractures and the formed artificial fractures are acidified to dissolve the calcium carbonate in the original fractures and the artificial fractures. The carbon dioxide generated during the acidification of the coal seam can further resolve and replace the methane (i.e. gas) in the coal seam, increase the gas content, and inertify the fire zone.

[0099] Step S105: After performing step S104, inject 5m 3 The concentration of the carbon dioxide aqueous solution is 0.02 mol / L and the temperature is 10 degrees. The injection pressure is 5 MPa and the construction displacement is 200 L / min.

[0100] After completing the above steps, the fracture permeability, gas content, gas extraction volume, and gas extraction rate are examined. The specific values ​​are shown in ( Figure 3 to Figure 6 ).

[0101] Embodiment 2

[0102] Temporary plugging and fracturing of medium and high-rank coalbed methane reservoirs are carried out through the following steps:

[0103] S101: preparing a fracturing fluid, wherein the fracturing fluid comprises a pumpkin seed extract having a plant enzyme activity of 8 mmol / min, a mixed solution of amide nitrogen fertilizer and calcium chloride having a concentration ratio of 1.5:1, a sodium lignin sulfonate solution having a concentration of 20 g / L, and a skimmed milk powder solution having a concentration of 5 g / L; the concentration of the amide nitrogen fertilizer is 0.75 mol / L, and the concentration of the calcium salt solution is 0.5 mol / L.

[0104] The method for preparing the plant extract in step S101 comprises the following steps:

[0105] S1011: At 4°C, select 60 kg of fresh and clean pumpkin seeds, crush them, and pass the crushed soybeans through a 120-mesh stainless steel sieve.

[0106] S1012: Add the plants sieved out from the mesh of the stainless steel sieve in step S1011 into a 2.5% Tris-CH3COOH (PH=6) buffer solution at a temperature of 4°C according to a solid-liquid ratio of 1:10, and shake well for 30 minutes to form a mixed solution.

[0107] S1013: Soak the mixed solution obtained in step S1012 in a 4°C refrigerator for 24 hours.

[0108] S1014: The mixed solution after immersion in step S1013 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 1000 rpm / min, homogenized for 2 minutes, allowed to stand for 3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 4000 rpm / min, and then the supernatant is collected.

[0109] S1015: Add the residue remaining after collecting the supernatant in step S1014 into a 2.5% Tris-CH3COOH (PH=6) buffer solution at a solid-liquid ratio of 1:10 at a temperature of 4°C and a concentration of 30 minutes to form a mixed solution.

[0110] S1016: Soak the mixed solution obtained in step S1015 in a 4°C refrigerator for 24 hours.

[0111] S1017: The mixed solution after soaking in step S1016 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 1000 rpm / min, homogenized for 2 minutes, allowed to stand for 3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 4000 rpm / min, and then the supernatant is collected.

[0112] S1018: The supernatant obtained in step S1014 and the supernatant obtained in step S1017 are mixed and filtered through 30 mm thick glass wool.

[0113] According to the above steps S1011-S1018, pumpkin seed extract can be obtained, the plant extract and 1 mol / L amide nitrogen fertilizer are mixed at a volume ratio of 1:9, and then the activity of the plant enzyme in the plant extract is detected. If the activity of the plant enzyme in the plant extract is within the range of 5-8 mmol / min, the plant extract is qualified. The qualified plant extract is placed in a refrigerator and stored at 4°C for use.

[0114] S102: Implement hydraulic fracturing, inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam.

[0115] According to formula 1:

[0116]

[0117] Calculation shows that the value of the expansion pressure Pz required to be provided to the coal seam is 32MPa, where: E is the elastic modulus of the coal body; γ is the surface energy per unit area; υ is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is an empirical coefficient, generally taken as 1.05~1.15.

[0118] According to formula 2:

[0119]

[0120] Calculation shows that the duration T of injecting active water into the coal seam is 145 minutes. In the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

[0121] Through testing and fracturing analysis, the changing characteristics of crack extension under different displacements were obtained, and the optimal crack width was determined to be 300L / min, which is the optimal construction displacement.

[0122] S103: The fracturing fluid is used to plug existing cracks and form new cracks. The fracturing fluid described in step S101 is repeatedly injected into the coal seam. The fracturing fluid generates calcium carbonate precipitates with cementing properties under the mineralization effect to plug artificial cracks and primary cracks in the coal seam, and press out new cracks in the coal seam.

[0123] In this step, the device for injecting fracturing fluid into the coal seam includes a three-way joint, a first grouting pipe connected to the three-way joint at one end, a first high-pressure pump connected to the other end of the first grouting pipe, a second grouting pipe connected to the three-way joint at one end, a second high-pressure pump connected to the other end of the second grouting pipe, and a third grouting pipe connected to the three-way joint at one end and inserted into the coal seam at the other end, the upper end of the third grouting pipe is connected to the three-way joint, and the lower end of the third grouting pipe is located in the coal seam after passing through the rock layer. When injecting fracturing fluid into the coal seam, the first high-pressure pump injects a mixed solution of lignin sulfonate solution, plant extract and skimmed milk powder solution in a volume ratio of 1:2:1 into the third grouting pipe at a flow rate of Q1=13L / min through the first grouting pipe; at the same time, the second high-pressure pump injects a mixed solution of amide nitrogen fertilizer and calcium salt into the third grouting pipe at a flow rate of Q1=39L / min through the second grouting pipe. The mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt are mixed in the third grouting pipe and then injected into the coal seam. The calcium carbonate precipitation generated by the mixture of lignin sulfonate solution, plant extract and skim milk powder solution and the mixture of amide nitrogen fertilizer and calcium salt temporarily blocks the artificial cracks and primary cracks in the coal seam, and further promotes the fracturing of the coal seam to expand the extension range of the cracks. Compared with the method of directly mixing the mixture of lignin sulfonate solution, plant extract and skim milk powder solution with the mixture of amide nitrogen fertilizer and calcium salt and injecting them into the coal seam through a pipeline, it can avoid the premature deposition of calcium carbonate at the injection port and causing pipeline blockage.

[0124] Each injection of fracturing fluid into the coal seam lasts for 12 hours. The time interval from the end of one injection of fracturing fluid into the coal seam to the start of the next injection of fracturing fluid into the coal seam is 12 hours. After four injections of fracturing fluid into the coal seam, the length of the main fracture reached 195m and the width reached 440mm.

[0125] S104: Inject acid solution into the coal seam for 10m 3 The concentration of CH3COOH is 15%, and the flow rate of CH3COOH injected into the coal seam is 50L / min. The original fractures and the formed artificial fractures are acidified to dissolve the calcium carbonate in the original fractures and the artificial fractures. The carbon dioxide generated during the acidification of the coal seam can further resolve and replace the methane (i.e. gas) in the coal seam, increase the gas content, and inertify the fire zone.

[0126] Step S105: After performing step S104, inject 5m 3 The concentration of the carbon dioxide aqueous solution is 0.04 mol / L and the temperature is 2 degrees. The injection pressure is 10 MPa and the construction displacement is 100 L / min.

[0127] After completing the above steps, the fracture permeability, gas content, gas extraction volume, and gas extraction rate are examined. The specific values ​​are shown in ( Figure 3 to Figure 6 ).

[0128] Embodiment 3

[0129] The medium and high rank coalbed methane reservoirs are fractured by the following steps:

[0130] S101: Implement hydraulic fracturing, inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam.

[0131] According to formula 1:

[0132]

[0133] Calculate the expansion pressure P required to provide to the coal seam z It is 32MPa, where: E is the elastic modulus of the coal body; γ is the surface energy per unit area; u is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is an empirical coefficient, generally taken as 1.05~1.15.

[0134] According to formula 2:

[0135]

[0136] Calculation shows that the duration T of injecting active water into the coal seam is 145 minutes. In the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

[0137] Through testing and fracturing analysis, the changing characteristics of crack extension under different displacements were obtained, and the optimal crack width was determined to be 300L / min, which is the optimal construction displacement.

[0138] S102: Repeatedly inject active water into the coal seam.

[0139] In this step, the device for injecting active water into the coal seam includes a three-way joint, a first grouting pipe with one end connected to the three-way joint, a first high-pressure pump connected to the other end of the first grouting pipe, a second grouting pipe with one end connected to the three-way joint, a second high-pressure pump connected to the other end of the second grouting pipe, and a third grouting pipe with one end connected to the three-way joint and the other end inserted into the coal seam, the upper end of the third grouting pipe is connected to the three-way joint, and the lower end of the third grouting pipe is located in the coal seam after passing through the rock layer. When injecting active water into the coal seam, the first high-pressure pump injects active water into the first grouting pipe at a flow rate of Q1=7L / min through the first grouting pipe; at the same time, the second high-pressure pump injects active water into the second grouting pipe at a flow rate of Q1=21L / min through the second grouting pipe.

[0140] Each injection of active water into the coal seam lasts for 12 hours. The time interval from the end of one injection of active water into the coal seam to the beginning of the next injection of active water into the coal seam is 12 hours. After injecting active water into the coal seam four times, the length of the main crack is 90.9m and the width reaches 225mm.

[0141] S103: Inject acid solution into the coal seam for 10m 3 The concentration of CH3COOH is 15%, and the flow rate of CH3COOH injected into the coal seam is 50L / min.

[0142] Step S104: inject 5m into the coal seam under normal temperature conditions 3 The concentration of the carbon dioxide aqueous solution is 0.02 mol / L and the temperature is 2 degrees. The injection pressure is 10 MPa and the construction displacement is 200 L / min.

[0143] After completing the above steps, the fracture permeability, gas content, gas extraction volume, and gas extraction rate are examined. The specific values ​​are shown in ( Figure 3 to Figure 6 ).

[0144] The first and second embodiments are the cases where the coal seam fractures have been transformed by fracturing fluid, and the third embodiment is the case where the coal seam fractures have not been fracturing transformed by fracturing fluid. Figure 3 to Figure 6 It can be directly seen that the coal seam fractures transformed by the fracturing fluid can greatly improve the fracture permeability, gas extraction quantity and gas extraction speed.

[0145] The results of fracture permeability, gas content, gas extraction quantity, and gas extraction rate in Examples 1-3 were analyzed.

[0146] like Figure 3 As shown, the permeability of the coal seams after transformation in Examples 1-2 is approximately 12.3 times that of Example 3 without temporary plugging.

[0147] like Figure 4As shown, under the condition that the gas content of the original coal seam is basically the same, the gas content of Examples 1-2 is about 30.6% lower than that of Example 3 on average.

[0148] like Figure 5 As shown, the average pure amount of gas extracted in Example 1-2 is about 4.2 times that of Example 3.

[0149] like Figure 6 As shown, the extraction speed of Example 1-2 is about 2.8 times that of Example 3.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes, characterized in that: The following steps are involved: S101: preparing a fracturing fluid, wherein the fracturing fluid comprises a plant extract having a plant enzyme activity of 5 to 8 mmol / min, a mixed solution of amide nitrogen fertilizer and calcium salt at a concentration ratio of 1.5:1, a lignin sulfonate solution having a concentration of 20 to 22 g / L, and a skim milk powder solution having a concentration of 5 to 10 g / L; the concentration of the amide nitrogen fertilizer is 0.75 to 1.05 mol / L, and the concentration of the calcium salt solution is 0.5 to 0.7 mol / L; S102: Perform hydraulic fracturing, inject active water into the coal seam to provide expansion pressure to the coal seam, so as to generate artificial cracks in the coal seam; S103: Reconstructing coal seam fractures by using the fracturing fluid, and repeatedly injecting the fracturing fluid described in step S101 into the coal seam for multiple times, wherein the fracturing fluid generates calcium carbonate precipitates with cementing properties under the mineralization effect to seal artificial fractures and primary fractures in the coal seam, and press out new fractures in the coal seam; S104: injecting an acid solution into the coal seam to acidify the original fractures and the formed artificial fractures, and dissolving the calcium carbonate in the original fractures and the artificial fractures; The method for preparing the plant extract in step S101 comprises the following steps: S1011: at 4° C., crushing the plant and passing the crushed plant through a 80-120 mesh sieve; S1012: adding the plants sieved out from the mesh of the sieve in step S1011 to carboxylesterase at a temperature of 4° C. and a concentration of 0.1 to 0.5 mg / ml or Tris-CH3COOH buffer at a temperature of 4° C. and a concentration of 2.5% to 3% at a solid-liquid ratio of 1:10, and shaking well for 25 to 30 minutes to form a mixed solution; S1013: Soak the mixed solution obtained in step S1012 in a 4° C. refrigerator for 24 hours; S1014: the mixed solution after immersion in step S1013 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected; S1015: adding the residue remaining after collecting the supernatant in step S1014 to a carboxylesterase having a temperature of 4° C. and a concentration of 0.1 to 0.5 mg / ml or a Tris-CH3COOH buffer having a temperature of 4° C. and a concentration of 2.5% to 3% at a solid-liquid ratio of 1:10, and shaking well for 25 to 30 minutes to form a mixed solution; S1016: Soak the mixed solution obtained in step S1015 in a 4° C. refrigerator for 24 hours; S1017: the mixed solution after soaking in step S1016 is placed on a magnetic stirrer, stirred for 1 hour at a temperature of 4°C and a rotation speed of 800-1000 rpm / min, homogenized for 2-5 minutes, allowed to stand for 2-3 hours, centrifuged for 20 minutes at a temperature of 4°C and a rotation speed of 3500-4000 rpm / min, and then the supernatant is collected; S1018: Mix the supernatant obtained in step S1014 and the supernatant obtained in step S1017 and filter them through 25-30 mm thick glass wool; The plant is soybean, pumpkin seed, watermelon seed, green bean, asparagus or spinach.

2. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: After performing step S104, a carbon dioxide aqueous solution with a concentration of 0.02-0.04 mol / L and a temperature of 2-10 degrees is injected into the coal seam under normal temperature conditions, the injection pressure is 5-10 MPa, and the construction displacement is 100L / min-200L / min.

3. A temporary plugging and fracturing method for medium and high-rank coalbed methane reservoirs based on plant enzymes according to any one of claim 1, characterized in that: The calcium salt in step S101 is one of calcium bromide, calcium iodide, calcium nitrate and calcium chloride, or a mixture of several thereof.

4. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: The lignin sulfonate in step S101 is sodium lignin sulfonate, calcium lignin sulfonate or potassium lignin sulfonate.

5. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: The value P of the expansion pressure required to be provided to the coal seam in step S102 z According to formula 1: Calculation shows that, in the above formula: E is the elastic modulus of the coal body; γ is the surface energy per unit area; v is the Poisson's ratio; a is half the length of the crack; σ is the minimum principal ground stress; α is the empirical coefficient, generally taken as 1.05~1.

15.

6. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: The duration T of injecting active water into the coal seam in step S102 is based on Formula 2: Calculation shows that, in the above formula: η is the porosity, which is 3% to 5%; k is the permeability coefficient; P1 is the water injection pressure; P2 is the initial gas pressure of the coal seam; r1 is the borehole radius; r2 is the radius of the gas-liquid contact surface; d is the distance between adjacent boreholes; μ1 is the viscosity coefficient of water; μ2 is the viscosity coefficient of gas.

7. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: The device for injecting fracturing fluid into the coal seam in the step S103 includes a tee joint, a first grouting pipe connected to the tee joint at one end, a first high-pressure pump connected to the other end of the first grouting pipe, a second grouting pipe connected to the tee joint at one end, a second high-pressure pump connected to the other end of the second grouting pipe, and a third grouting pipe connected to the tee joint at one end and inserted into the coal seam at the other end; when injecting fracturing fluid into the coal seam in the step S103, the first high-pressure pump injects a mixed solution of lignin sulfonate solution, plant extract and skimmed milk powder solution in a volume ratio of 1:2:1 into the third grouting pipe at a flow rate of Q1=7~13L / min through the first grouting pipe; at the same time, the second high-pressure pump injects a mixed solution of amide nitrogen fertilizer and calcium salt into the third grouting pipe at a flow rate of 3Q1 through the second grouting pipe.

8. The method for temporary plugging and fracturing of medium- and high-rank coalbed methane reservoirs based on plant enzymes according to claim 1, characterized in that: The acidic solution in step S104 is CH3COOH with a concentration of 15%, and the flow rate of CH3COOH injected into the coal seam is 50 L / min.

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