Microwave-hydraulic power combined anti-reflection pressure relief and gas extraction method

Abstract

The invention belongs to the technical field of coal mine safety mining, and relates to a microwave-hydraulic power combined permeability-increasing pressure relief and gas extraction method, which comprises the following steps of: firstly, carrying out geological survey and coal sample test to obtain physical and mechanical parameters of a coal seam; calculating the fracture pressure of the coal seam according to the parameters and determining hydraulic fracturing and microwave irradiation parameters; a hydraulic fracturing drill hole and a microwave irradiation drill hole are constructed; fracturing, irradiation and monitoring equipment is installed; performing low-frequency microwave preheating on the coal seam, and then performing staged hydraulic fracturing; the fracturing effect is evaluated through micro-seismic monitoring, and a weak area is marked; and finally, high-frequency microwave enhanced irradiation is carried out in the weak area, and meanwhile gas extraction is carried out. According to the method, through the synergistic effect of microwave thermal cracking and hydraulic fracturing, the coal seam permeability and the gas desorption efficiency are remarkably improved, meanwhile, the rock burst risk is reduced, safe and efficient gas extraction is achieved, and a reliable technical scheme is provided for high-gas coal seam mining.

Description

Technical Field

[0001] The present invention relates to the technical field of safe coal mining, and specifically to a microwave - hydraulic combined permeability enhancement, pressure relief and gas extraction method. Background Art

[0002] The prevention and control of rock bursts and coal and gas outbursts are key parts of the technical field of safe coal mining. With the continuous increase in the depth and intensity of coal mining, the risks of rock bursts and coal and gas outbursts are increasing day by day, seriously threatening coal mine safety production and the lives of personnel. This field is committed to developing a series of technical means to achieve the purpose of preventing and controlling disasters by studying and regulating factors such as the mechanical properties of coal and rock masses and the gas occurrence state. Among them, hydraulic fracturing technology creates fractures in coal seams to improve the permeability of coal masses, promote gas emission and reduce the stress of coal masses; microwave irradiation technology uses the interaction between microwaves and coal masses to change the coal mass structure and enhance the gas desorption and migration ability. Gas extraction technology is to extract the gas in coal seams, reduce the gas content and reduce the potential risk of disasters.

[0003] In traditional technologies, for the prevention and control of rock bursts and coal and gas outbursts, hydraulic fracturing usually adopts a construction method with fixed parameters. Based on experience or simple geological data, the aperture, hole spacing and stage spacing of hydraulic fracturing are determined, and there is less dynamic adjustment according to the actual changes of coal masses during the construction process. For microwave irradiation, a single frequency and power setting are often used, without fully considering the differences in coal mass characteristics in different regions and operation stages, and it is impossible to accurately irradiate different coal mass parts effectively. In terms of gas extraction, traditional methods mainly rely on fixed extraction equipment and processes, and have insufficient response to the dynamic changes in the gas occurrence state of coal masses under the action of fracturing, microwave irradiation, etc., making it difficult to achieve efficient extraction. In the geological investigation and coal sample determination links, the data collected by traditional means are limited and the accuracy is not high, and the understanding of the physical and mechanical properties and geological conditions of coal masses is not comprehensive and in - depth enough, resulting in a lack of sufficient scientific basis for determining subsequent operation parameters.

[0004] Therefore, we propose a microwave - hydraulic combined permeability enhancement, pressure relief and gas extraction method. Summary of the Invention

[0005] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] A microwave - hydraulic combined permeability enhancement, pressure relief and gas extraction method includes the following steps:

[0007] S1: Conduct on-site geological investigation and coal seam sampling, and determine the basic physical and mechanical properties of the coal samples.

[0008] S2: Determine the hydraulic fracturing hole diameter D, hole spacing l h , section spacing l, and the microwave irradiation range at different frequencies.

[0009] S3: Construct directional long-distance fracturing and gas drainage boreholes (Type I boreholes) and microwave irradiation boreholes (Type II boreholes).

[0010] S4: Install hydraulic fracturing equipment, microwave irradiation equipment, gas drainage equipment and monitoring equipment.

[0011] S5: Conduct microwave low-frequency irradiation in the Type I boreholes to preheat the coal seam.

[0012] S6: Conduct staged hydraulic fracturing in the Type I boreholes.

[0013] S7: Evaluate the fracturing pressure relief effect through microseismic monitoring, and mark the areas with good and poor fracturing effects.

[0014] S8: Conduct microwave high-frequency radiation in the Type II boreholes to enhance the fracturing effect and gas desorption, and cooperate with the gas drainage of the Type I boreholes.

[0015] Preferably, the frequency of the microwave low-frequency irradiation is 915 MHz, the power is 10 kW, the irradiation time is 20 - 40 minutes, and the coal body temperature is controlled between 150°C and 200°C.

[0016] Preferably, the frequency of the microwave high-frequency radiation is 2.45 GHz or 3.55 GHz, the power is 3 kW - 5 kW, the irradiation time is 10 - 20 minutes, and the coal body temperature is controlled between 150°C and 200°C.

[0017] Preferably, the hydraulic fracturing parameters are determined by the coal seam fracture pressure calculation formula, and the formula is:

[0018]

[0019] In the formula, P F is the fracture initiation pressure of the rock, σh is the minimum principal stress, σH is the maximum principal stress, σf is the tensile strength, is the rock porosity, υ is the Poisson's ratio, and p0 is the pore fluid pressure.

[0020] Preferably, the microwave irradiation range is calculated by the following formula:

[0021]

[0022] Among them, λ is the microwave wavelength, ε is the dielectric constant, and α is the absorption coefficient.

[0023] Preferably, the microseismic monitoring evaluates the fracturing effect through the microseismic frequency kernel density and the energy kernel density, and the calculation formulas are as follows:

[0024]

[0025] where ρ N is the microseismic frequency kernel density, ρ E is the microseismic energy kernel density, i is the number of microseismic events, (ΣE i ) j is the energy of the microseismic event, and V j is the volume of the unit space j.

[0026] Advantages of the present invention:

[0027] Through the microwave-hydraulic combined permeability enhancement and pressure relief technology, the present invention realizes the synergistic effect of efficient coal seam permeability enhancement and enhanced gas extraction. Microwave preheating promotes thermal fracture of the coal body and reduces the mechanical strength, effectively reducing the initiation pressure of hydraulic fracturing. At the same time, the thermal effect promotes gas desorption; staged hydraulic fracturing forms a three-dimensional fracture network, combined with microseismic monitoring technology to dynamically evaluate the fracturing effect and mark weak areas; subsequent high-frequency microwave irradiation enhances fracture propagation and avoids coal body sintering through precise temperature control. This method significantly improves the gas extraction efficiency, while reducing the risk of rock burst, forming a closed-loop technical system of "microwave pretreatment - hydraulic fracturing - microwave enhancement - synergistic extraction". This technology combines engineering safety and economy, with high equipment reuse rate, providing a reliable technical support for the safe and efficient mining of deep high-gas coal seams. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Among them:

[0030] Figure 1 is a schematic diagram of the construction of directional long-distance fracturing + gas extraction boreholes of type I and microwave irradiation boreholes of type II;

[0031] Figure 2 is a flow chart for microwave high-frequency radiation in boreholes of type II to enhance the fracturing effect and gas desorption, and synergistically extract gas from boreholes of type I; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to make the object, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0033] Embodiment:

[0034] As Figure 1 and Figure 2 shown, a microwave-hydraulic combined permeability enhancement, pressure relief, and gas drainage method includes the following specific steps:

[0035] I. On-site geological investigation and coal seam sampling to determine the basic physical and mechanical properties of coal samples:

[0036] (1) Conduct engineering geological investigations in mines with rock burst and coal and gas outburst disasters, and collect basic geological data, including the coal quality, gas content, coal seam thickness, coal seam hardness, and stratum stress distribution characteristics of each coal seam. Take coal samples at positions where the coal seam has no obvious fissures and is intact;

[0037] (2) Determine the uniaxial compressive strength σ C , elastic modulus E, density ρ, dielectric constant ε, absorption coefficient α, etc., tensile strength σf, rock porosity φ, and Poisson's ratio υ of the coal samples in the laboratory.

[0038] II. Determine the hydraulic fracturing hole diameter D, hole spacing lh, and section spacing l, and determine the microwave irradiation range at different frequencies:

[0039] (1) Calculate the coal seam fracture pressure based on the measured physical and mechanical parameters of the coal seam. The calculation formula is as follows:

[0040]

[0041] In the formula, PF is the initial fracture pressure of the rock, σh is the minimum principal stress, σH is the maximum principal stress, σf is the tensile strength, φ is the rock porosity (generally taking values of 20% - 30% for hard sandstone), υ is Poisson's ratio, and p0 is the pore fluid pressure;

[0042] (2) Based on the calculation results of the coal seam fracture pressure, use comsol numerical simulation software and combine the actual physical and mechanical parameters to simulate and analyze the sectional hydraulic fracturing construction parameters including the fracture propagation range, fracturing section spacing, fracturing water injection volume, and fracturing borehole spacing;

[0043] (3) Calculate the irradiation range at different microwave frequencies. The calculation formula is as follows:

[0044]

[0045] In the formula, λ is the microwave wavelength.

[0046] III. Construction of directional long-distance fracturing + gas drainage boreholes, type I boreholes, and microwave irradiation, type II boreholes:

[0047] Use a directional drilling rig to drill boreholes in the coal seam to ensure the stability and straightness of the boreholes, and ensure that subsequent hydraulic fracturing pipes and microwave irradiation pipes can smoothly enter the boreholes. According to the aforementioned fracturing hole spacing, construct hydraulic fracturing boreholes (which are also subsequent gas drainage boreholes), mark them as type I boreholes, and construct small-diameter microwave irradiation boreholes between two hydraulic fracturing boreholes, and mark them as type II boreholes.

[0048] IV. Prepare and install hydraulic fracturing, microwave irradiation, gas drainage, temperature sensors, and gas concentration monitoring equipment:

[0049] (1) Install hydraulic fracturing equipment (including a pumping station, fracturing fluid storage system, control system, and fracturing pipeline), microwave radiation equipment (including a microwave generator, multi-frequency control system, cooler, microwave emitter, waveguide + antenna, and microwave protection tube), and gas drainage equipment (including a drainage pumping station, drainage pipeline, and filter) in the drill site, prepare temperature sensors, and arrange gas concentration monitoring equipment outside the roadway;

[0050] (2) Arrange three-component microseismic sensors in the roadways on both sides of the working face. The spacing between the microseismic sensors is 50 m, and they are installed in the middle of the coal wall. The sensor arrangement range covers the entire fracturing range;

[0051] V. Conduct microwave low-frequency irradiation in type I boreholes to preheat the coal seam:

[0052] (1) Connect the microwave waveguide to the microwave antenna and place them in the microwave protection tube, and then send them together into the type I borehole until the bottom of the hole. At the same time, send the temperature sensor to the bottom of the borehole;

[0053] (2) Start the microwave generator, adjust the microwave irradiation frequency to the low-frequency 915 MHz, and the microwave power to 10 kW, and synchronously monitor the temperature;

[0054] (3) Start irradiating the first section of the coal body, and at the same time monitor the temperature of the coal body. Keep the temperature of the coal body between 150°C and 200°C. When the temperature is higher than 200°C, stop irradiation. When it is lower than 150°C, start irradiation, and conduct intermittent microwave irradiation. Stop after 20 - 40 minutes of irradiation;

[0055] (4) Adjust the position of the microwave protection tube according to the penetration range x of the low-frequency microwave irradiation calculated above. Withdraw the microwave catheter, microwave antenna, and the microwave protection tube together backward by a distance x, and at the same time, also withdraw the temperature sensor by a distance x.

[0056] (5) Start irradiating the second section of the coal body, and at the same time monitor the temperature of the coal body, which is the same as in step (3) above. Continue until the microwave irradiation retreats to 15 m from the borehole orifice, then stop the irradiation and withdraw the microwave catheter, antenna, protection tube, and temperature sensor.

[0057] VI. Conducting staged hydraulic fracturing of the coal seam in Type I boreholes:

[0058] (1) Send the hydraulic fracturing pipe into the Type I borehole to the bottom position of the borehole.

[0059] (2) Start the high-pressure pump for hydraulic fracturing and begin the first-stage fracturing operation. Monitor the pump injection pressure and flow rate curves to ensure the normal setting of the packer.

[0060] (3) Move the fracturing pipe backward according to the previously obtained fracturing section spacing, and start the second-stage and subsequent fracturing until the entire coal seam is fractured.

[0061] (4) After the fracturing is completed, drain the water through the orifice valve group, install the blowout prevention device, and control the drainage volume. There will be coal slag remaining in the borehole after the drainage, and a borehole washing operation is required.

[0062] VII. Evaluating the effect of fracturing for pressure relief and impact prevention, and marking the areas with insufficient fracturing:

[0063] (1) Synchronously start the microseismic monitoring after the fracturing begins, and transmit the microseismic data to the data integration system in real time.

[0064] (2) Judge the fracture propagation range of the fracturing through the microseismic frequency kernel density. The calculation formula is as follows:

[0065]

[0066] In the formula: ρ N is the microseismic event frequency kernel density value, (∑N i ) j is the total number of all microseismic events in the unit space j, V j is the volume of the unit space j, i is the number of microseismic events, and j is the number of unit spaces;

[0067] (3) Judge the fracture propagation intensity of the fracturing through the microseismic energy kernel density. The calculation formula is as follows:

[0068]

[0069] In the formula: ρ E is the microseismic event energy kernel density value, (∑Ei ) j is the total energy of all microseismic events in unit space j. V j is the volume of unit space j, i is the number of microseismic events, and j is the number of unit spaces;

[0070] (4) Mark the areas with good and poor fracturing effects. The fracture propagation is insufficient in the low-value area of the microseismic frequency kernel density, and the fracture propagation is small in the low-value area of the microseismic energy kernel density. Mark the area where both the microseismic frequency kernel density and the energy kernel density are small as the area with poor fracturing effect, mark the area where either the microseismic frequency kernel density or the energy kernel density is small as the area with better fracturing effect, and mark the other areas as the areas with good fracturing effect.

[0071] VIII. Carry out microwave high-frequency radiation to enhance the fracturing effect and gas desorption in Class II boreholes, and cooperate with the gas extraction in Class I boreholes:

[0072] (1) Place the extraction pipe into the Class I borehole to the bottom, place the grouting pipe at the front end of the borehole, place polyurethane at both ends of the borehole for plugging, and grout in the middle between the two polyurethanes. The sealing length is 15 m;

[0073] (2) Connect the microwave irradiation catheter with the antenna, place it into the microwave protection tube 5, nest and combine the microwave protection tube 5 with the external thread tube 4, place it in the Class II borehole 2, place polyurethane at both ends of the external thread tube 4 for plugging, and grout in the middle between the two polyurethanes. The sealing length is 15 m;

[0074] (3) Start the microwave generator. Adjust the microwave irradiation frequency to 2.45 GHz and the microwave power to 5 kW in the area with good fracturing effect marked. Adjust the microwave irradiation frequency to 3.55 GHz and the microwave power to 3 kW in the area with poor fracturing effect marked. Synchronously monitor the temperature. At the same time, start the gas extraction pump for negative pressure extraction. While enhancing the fracturing effect by secondary irradiation, further desorb the gas and preheat the next section of the fractured coal body at the same time;

[0075] (4) Start irradiating the first section of the coal body, and at the same time monitor the temperature of the coal body, maintain the temperature of the coal body between 150° and 200°. Stop irradiation when the temperature is higher than 200°, and start irradiation when it is lower than 150°. Carry out intermittent microwave irradiation and stop after 10 - 20 minutes of irradiation;

[0076] (5) Adjust the position of the microwave protection tube according to the low-frequency microwave irradiation penetration range x calculated above. Withdraw the microwave catheter, microwave antenna and microwave protection tube together with the external thread tube backward by a distance x, and at the same time withdraw the temperature sensor by a distance x;

[0077] (6) Start irradiating the second section of the coal body, and simultaneously monitor the temperature of the coal body, which is the same as in the previous step (3). Continue until the microwave irradiation retreats to 15 m from the borehole orifice (sealing position), then stop the irradiation and withdraw the microwave conduit 5, the antenna, the external threaded pipe 4, and the temperature sensor.

[0078] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above-described embodiments and descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all such changes and improvements fall within the scope of the present invention as claimed. The scope of the present invention as claimed is defined by the appended claims and their equivalents.

Claims

1. A microwave - hydraulic combined permeability enhancement, pressure relief and gas drainage method, characterized in that It includes the following steps: S1: Conduct on-site geological investigation and coal seam sampling, and determine the basic physical and mechanical properties of coal samples; S2: Determine the hydraulic fracturing pore diameter D, pore spacing l h , stage spacing l, and the microwave irradiation range at different frequencies; S3: Construct directional long-distance fracturing and gas drainage boreholes (Type I boreholes) and microwave irradiation boreholes (Type II boreholes); S4: Install hydraulic fracturing equipment, microwave irradiation equipment, gas drainage equipment and monitoring equipment; S5: Conduct microwave low-frequency irradiation in Type I boreholes to preheat the coal seam; S6: Conduct staged hydraulic fracturing in Type I boreholes; S7: Evaluate the fracturing pressure relief effect through microseismic monitoring, and mark the areas with good and poor fracturing effects; S8: Conduct microwave high-frequency radiation in Type II boreholes to enhance the fracturing effect and gas desorption, and cooperate with the gas drainage of Type I boreholes.

2. The method according to claim 1, characterized in that, The frequency of the microwave low-frequency irradiation is 915 MHz, the power is 10 kW, the irradiation time is 20 - 40 minutes, and the coal body temperature is controlled between 150°C and 200°C.

3. The method according to claim 1, wherein The frequency of the microwave high-frequency radiation is 2.45 GHz or 3.55 GHz, the power is 3 kW - 5 kW, the irradiation time is 10 - 20 minutes, and the coal body temperature is controlled between 150°C and 200°C.

4. The method according to claim 1, wherein The hydraulic fracturing parameters are determined by the coal seam fracture pressure calculation formula, and the formula is: where P F is the fracture initiation pressure of the rock, σh is the minimum principal stress, σH is the maximum principal stress, and σf is the tensile strength, is the porosity of the rock formation, υ is the Poisson's ratio, and p0 is the pore fluid pressure.

5. The method according to claim 1, characterized in that, The microwave irradiation range is calculated by the following formula: where λ is the microwave wavelength, ε is the dielectric constant, and α is the absorption coefficient.

6. The method according to claim 1, characterized in that, The microseismic monitoring evaluates the fracturing effect through microseismic frequency kernel density and energy kernel density, and the calculation formulas are respectively: Among them, ρ N is the microseismic frequency kernel density, ρ E is the microseismic energy kernel density, i is the number of microseismic events, (∑E i ) j is the energy of the microseismic event, and V j is the volume of the unit space j.

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