Ultrasonic coal seam anti-reflection effect evaluation method based on multi-parameter joint monitoring

Abstract

The invention belongs to the technical field of coal seam gas extraction efficiency improvement, and relates to a coal seam ultrasonic anti-reflection effect evaluation method based on multi-parameter combined monitoring. The ultrasonic anti-reflection effect is comprehensively monitored through multiple means, and comprehensive evaluation on improvement of the gas extraction efficiency is achieved. Firstly, by monitoring parameters of an ultrasonic generator, it is ensured that ultrasonic waves stably operate according to set parameters; secondly, by monitoring a coal body structure, stress distribution, gas concentration and a microseism event, the physical change and gas release condition of the target coal body under the action of the ultrasonic field are evaluated; then, the gas extraction efficiency is calculated by monitoring the gas extraction flow and concentration, and the influence of ultrasonic anti-reflection on the coal seam gas extraction effect is evaluated. And then, the durability of the ultrasonic anti-reflection effect is evaluated by tracking and monitoring the change rate of the gas extraction efficiency for a long time. Finally, by calculating the improvement rate of the gas extraction efficiency, a judgment standard is established, and the improvement effect of the ultrasonic anti-reflection on the gas extraction efficiency is comprehensively evaluated.

Description

Technical Field

[0001] The present invention belongs to the technical field of improving gas extraction efficiency in coal seams, and relates to a method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring. Background Art

[0002] Coalfields typically use a central parallel extraction ventilation method to control gas outbursts and prevent gas over-limits. However, this extraction method requires high initial investment, a long operation cycle, and poor economic benefits. The vast majority of my country's coalfields are low-permeability coal seams. While various coal seam fracturing and permeability enhancement technologies have been proposed, such as hydraulic fracturing, electric pulse shock wave, high-pressure air blasting, and carbon dioxide blasting, these technologies have achieved successful application in coal mine gas outbursts, coalfield gas control, and coalbed methane extraction. However, these technologies still face numerous challenges in terms of technical applicability, economic efficiency, and safety.

[0003] Ultrasound is a highly penetrating mechanical wave that can exert cavitation and mechanical effects on coal seams, accompanied by thermal and chemical effects, accelerating the separation and diffusion of gas (methane) molecules from the coal matrix. Chinese invention patent CN109707435B discloses a system and method for improving coal seam gas extraction using a combined acoustic field and hydraulic fracturing technology. This method, which applies an ultrasonic field after hydraulic fracturing, can promote gas extraction and offers advantages in terms of technical applicability, economy, and safety. However, methods for real-time monitoring of whether ultrasonic waves increase coal seam permeability and gas extraction efficiency in mines have not been reported. Therefore, there is an urgent need for a method that can comprehensively monitor the ultrasonic permeability enhancement effect and evaluate its effect on gas extraction efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring. This method evaluates the effect of ultrasonic cavitation effect on improving the permeability of coal seams and the changes in gas extraction efficiency under the action of ultrasonic permeability enhancement by comprehensively monitoring multi-dimensional indicators such as ultrasonic parameters, coal body structure changes, and gas extraction data.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring includes the following steps: Step 1: Real-time monitoring of the operating status of the ultrasonic generator in ultrasonic anti-reflection gas extraction; Step 2: Monitor the target coal body status; conduct real-time monitoring of the target coal body's structural changes, stress distribution, gas concentration, and microseismic events, and evaluate the target coal body's physical changes and gas release under the action of the ultrasonic field; Step 3: Monitor the gas drainage status, calculate the gas drainage efficiency W1 based on the monitoring data, calculate the gas drainage efficiency W1 before and after ultrasonic coal seam permeability enhancement, and evaluate whether the ultrasonic permeability enhancement is effective for gas drainage; if effective, track and monitor the rate of change of the gas drainage efficiency W1 over time W2 to evaluate the durability of the ultrasonic permeability enhancement effect. The gas drainage efficiency , where c represents the gas drainage flow rate; v represents the gas drainage concentration; t represents the unit time; m represents the coal seam resource quantity; q represents the gas concentration before drainage. Step 4: Calculate the gas drainage efficiency improvement rate W3 to evaluate the ultrasonic permeability enhancement effect. ; where Q is the gas concentration change rate; A is the ultrasonic amplitude; H is the ultrasonic pulse width; t is the ultrasonic action time; P is the output power of the ultrasonic generator. is a step function, when x is a specific ultrasonic frequency , otherwise it is 0; K t1 is the coal body permeability at time t1; K t2 is the coal body permeability at time t2; Tex is the fracture line density; S is the number of microseismic events per unit time. When 0 < W3 ≤ 1.2, the ultrasonic permeability enhancement effect is poor; 1.2 < W3 ≤ 2.5, the ultrasonic permeability enhancement effect is medium; 2.5 < W3 ≤ 3.7, the ultrasonic permeability enhancement effect is good; 3.7 < W3, the ultrasonic permeability enhancement effect is excellent.

[0007] Furthermore, the operating state of the ultrasonic generator in Step 1 includes output power, ultrasonic frequency, ultrasonic pulse width, ultrasonic amplitude, action time, and emission angle; monitor the real-time changes of the operating state parameters to achieve the monitoring of the stable operating state of the ultrasonic wave.

[0008] Furthermore, the target coal body state in Step 2 includes coal body permeability, fracture line density, internal stress, gas concentration, and microseismic events.

[0009] Furthermore, take pictures of the interior of the target coal body through a digital panoramic borehole camera, and obtain the structural change situation by analyzing the image information; the distributed optical fiber sensing system is used to monitor the internal stress; the methane detector is used to monitor the gas concentration; the microseismic monitoring system is used to monitor microseismic events.

[0010] Furthermore, in Step 4, the tracking and monitoring of the gas drainage efficiency W1 should last for at least three months.

[0011] The beneficial effects of the present invention are: by comprehensively monitoring the ultrasonic permeability enhancement effect through various means, a comprehensive evaluation of the improvement in gas extraction efficiency is achieved. First, by monitoring the parameters of the ultrasonic generator, it is ensured that the ultrasonic wave operates stably according to the set parameters. Secondly, by monitoring the coal body structure, stress distribution, gas concentration and microseismic events, the physical changes and gas release of the target coal body under the action of the ultrasonic field are evaluated. Then, by monitoring the gas extraction flow and concentration, the gas extraction efficiency is calculated, and the impact of ultrasonic permeability enhancement on the gas extraction effect is evaluated. Next, by long-term tracking and monitoring the rate of change of gas extraction efficiency, the durability of the ultrasonic permeability enhancement effect is evaluated. Finally, by calculating the gas extraction efficiency improvement rate, a discrimination standard is established to comprehensively evaluate the effect of ultrasonic permeability enhancement on the improvement of gas extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the process of the present invention.

[0013] Figure 2 This is a real-time recorded data graph of gas extraction efficiency W1 changing with time.

[0014] Figure 3 Schematic diagram of the time series database of gas extraction efficiency change rate W2. DETAILED DESCRIPTION

[0015] 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 only part of the embodiments of the present invention, rather than all the embodiments.

[0016] like Figure 1 As shown, this embodiment discloses a method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring, comprising the following steps:

[0017] Step 1: Monitor the operating status of the ultrasonic generator; This embodiment is based on ultrasonic field enhanced transmittance gas extraction technology. Therefore, it is necessary to monitor the operating status of the ultrasonic generator in ultrasonic enhanced transmittance gas extraction in real time. The operating status data of the ultrasonic generator includes output power (W), ultrasonic frequency (Hz), ultrasonic pulse width (μs), ultrasonic amplitude (mm), action time (s) and emission angle (°); monitor the real-time changes in the operating status parameters to ensure the stable operation of the ultrasonic wave and provide benchmark data for subsequent effect evaluation.

[0018] Step 2: Monitor the target coal state; Real-time monitoring of the target coal's structural changes, stress distribution, gas concentration, and microseismic events is performed to assess physical changes and gas release in the target coal under the influence of the ultrasonic field. Target coal state data includes coal permeability (mD), fracture density (fractures / m), internal stress (stress magnitude and direction), gas concentration (%), and microseismic events (number of occurrences) to assess physical changes and gas release in the target coal under the influence of the ultrasonic field.

[0019] To monitor the state of the target coal body, technical means include a digital panoramic borehole camera, a distributed fiber optic sensing system, a methane detector, and a microseismic monitoring system. The digital panoramic borehole camera is used to capture images of the interior of the target coal body, and structural changes are acquired by analyzing the image information. The distributed fiber optic sensing system is used to monitor internal stress; the methane detector is used to monitor gas concentration; and the microseismic monitoring system is used to monitor microseismic events.

[0020] Step 3: Monitor gas extraction status; The gas extraction process is monitored, and the gas extraction efficiency W1 is calculated based on the monitoring data to evaluate the impact of coal seam ultrasonic field permeability enhancement on gas extraction results.

[0021] During the gas extraction process, the monitoring data include gas extraction flow c (m³ / h), gas extraction concentration v (%), gas extraction time t (h), coal seam resource m (t), and gas concentration before extraction q (m³ / t).

[0022] The gas extraction efficiency , where c represents the gas extraction flow rate; v represents the gas extraction concentration; t represents the unit time; m represents the coal seam resource volume; and q represents the gas concentration before extraction.

[0023] Step 4: Monitor the rate of change of gas extraction efficiency W1 over time; After ultrasonic anti-reflection treatment, the gas extraction efficiency W1 is tracked and monitored over a long period of time, and the rate of change of gas extraction efficiency over time is recorded in real time to establish a time series database to evaluate the durability of the ultrasonic anti-reflection effect.

[0024] The long-term tracking and monitoring time should be at least 3 months. The calculation model of the change rate of gas extraction efficiency over time W2 is as follows: ;in, Indicates the gas extraction efficiency in the current time period; is the gas extraction efficiency in the previous time period.

[0025] The durability of the ultrasonic anti-reflection effect was evaluated based on the change rate W2 of the gas extraction efficiency before and after the ultrasonic anti-reflection treatment.

[0026] Step 5: Calculate the improvement rate W3 of gas drainage efficiency, and establish a discrimination criterion for comprehensively monitoring whether the ultrasonic cavitation effect can improve gas drainage efficiency by various means.

[0027] If the gas concentration change rate Q is less than 0.1%, it is regarded as the failure of ultrasonic permeability enhancement, and the improvement rate of gas drainage efficiency, W3 = 0.

[0028] If the gas concentration change rate Q is greater than or equal to 0.1%, the calculation formula of W3 is as follows, ; Combined with the index requirements of gas drainage time and drainage compliance time, 0 < W3 ≤ 1.2, it indicates that the ultrasonic cavitation effect can improve gas drainage efficiency, but the effect is poor; 1.2 < W3 ≤ 2.5, the effect is medium; 2.5 < W3 ≤ 3.7, the effect is good; 3.7 < W3, the effect is excellent.

[0029] Taking the use of ultrasonic permeability enhancement to drain coal seam gas before coal mining as an example to verify the effectiveness of this embodiment.

[0030] (1) Monitor the parameters of the ultrasonic generator: output power P: 100KW; frequency x: 40kHz; pulse width H: 100μs; amplitude A: 0.05mm; action time t: 3600s.

[0031] (2) Monitor the coal body and gas data: coal body permeability K: increased from 0.05mD to 0.1mD; fracture line density Tex: increased from 2 pieces / meter to 10 pieces / meter; gas concentration ( ) increased from 2% to 3%; the number of microseismic events S: increased from 10 times / hour to 30 times / hour.

[0032] (3) Calculate the gas drainage efficiency W1: Before ultrasonic permeability enhancement, W 1t1 was 20%, and after ultrasonic permeability enhancement, W 1t2 increased to 30%, and the tracking monitoring is as Figure 2 shown.

[0033] (4) Calculate the change rate of gas drainage efficiency W2 = (30% - 20%) / 20% × 100% = 50%. The time series database of the change rate of gas drainage efficiency W2 is as Figure 3 shown.

[0034] (5) Calculate the improvement rate of gas drainage efficiency .

[0035] (6) W3 = 2.72; According to the discrimination criterion, 2.5 < W3 ≤ 3.7, indicating that the ultrasonic permeability enhancement effect is good and can effectively improve gas drainage efficiency.

[0036] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring, characterized in that: It includes the following steps: Step 1: Monitor the operating status of the ultrasonic generator in ultrasonic enhanced gas drainage in real time; Step 2: Monitor the target coal seam status; monitor the structural changes, stress distribution, gas concentration, and microseismic events of the target coal seam in real time, and evaluate the physical changes and gas release of the target coal seam under the action of ultrasonic waves; Step 3: Monitor the gas drainage status of the coal seam, calculate the gas drainage efficiency W1 based on the monitoring data, calculate the gas drainage efficiency before and after ultrasonic enhancement of the coal seam, and evaluate whether ultrasonic enhancement is effective in improving the gas drainage efficiency; if ultrasonic enhancement is effective for gas drainage, track and monitor the change rate W2 of the gas drainage efficiency W1 over time to evaluate the persistence of the ultrasonic enhancement effect; The gas extraction efficiency , where c represents the gas extraction flow rate; v represents the gas extraction concentration; t represents the unit time; m represents the coal seam resource; q represents the gas concentration before extraction; Step 4: Calculate the gas drainage efficiency improvement rate W3 to evaluate the ultrasonic enhancement effect; ； Wherein, Q is the rate of change of gas concentration; A is the ultrasonic amplitude; H is the ultrasonic pulse width; t is the ultrasonic action time; P is the output power of the ultrasonic generator; is a step function. When x is a specific ultrasonic frequency, , otherwise it is 0; K t1 is the coal permeability at time t1; K t2 is the coal permeability at time t2; Tex is the fracture line density; S is the number of microseismic events per unit time; When 0 < W3 ≤ 1.2, the ultrasonic enhancement effect is poor; 1.2 < W3 ≤ 2.5, the ultrasonic enhancement effect is medium; 2.5 < W3 ≤ 3.7, the ultrasonic enhancement effect is good; 3.7 < W3, the ultrasonic enhancement effect is excellent.

2. The method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring according to claim 1, characterized in that: The operating status of the ultrasonic generator in Step 1 includes output power, ultrasonic frequency, ultrasonic pulse width, ultrasonic amplitude, action time, and emission angle; monitor the real-time changes of the operating status parameters to achieve the monitoring of the stable operating status of the ultrasonic wave.

3. The method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring according to claim 1, characterized in that: The target coal seam status in Step 2 includes coal seam permeability, fracture line density, internal stress, gas concentration, and microseismic events.

4. The method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring according to claim 3 is characterized in that: Take pictures of the interior of the target coal seam through a digital panoramic borehole camera, and obtain the structural change situation by analyzing the image information; the distributed optical fiber sensing system is used to monitor the internal stress; the methane detector is used to monitor the gas concentration; the microseismic monitoring system is used to monitor microseismic events.

5. The method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring according to claim 1, characterized in that: In Step 3, tracking and monitoring the gas drainage efficiency W1 takes at least three months.

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