An ultrasonic coal seam permeability enhancement effect evaluation method based on multi-parameter joint monitoring

Abstract

The present application belongs to the technical field of coal seam gas extraction efficiency, and relates to a coal seam ultrasonic permeability enhancement effect evaluation method based on multi-parameter joint monitoring; the ultrasonic permeability enhancement effect is comprehensively monitored by various means to realize comprehensive evaluation of the improvement of gas extraction efficiency. First, the ultrasonic generator parameters are monitored to ensure that the ultrasonic waves operate stably according to the set parameters. Second, the coal body structure, stress distribution, gas concentration and microseismic events are monitored to evaluate the physical changes of the target coal body and the gas release under the action of the ultrasonic field. Then, the gas extraction flow and concentration are monitored to calculate the gas extraction efficiency and evaluate the influence of ultrasonic permeability enhancement on the coal seam gas extraction effect. Next, the change rate of the gas extraction efficiency is tracked and monitored for a long time to evaluate the persistence of the ultrasonic permeability enhancement effect. Finally, the gas extraction efficiency improvement rate is calculated to establish a discrimination standard and comprehensively evaluate the improvement effect of the ultrasonic permeability enhancement on the gas extraction efficiency.

Description

A method for evaluating the permeability enhancement effect of ultrasonic coal seams based on multi-parameter joint monitoring Technical Field

[0001] This invention belongs to the technical field of coal seam gas extraction efficiency improvement, and relates to a method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring. Background Technology

[0002] Coalfields typically employ a central parallel exhaust ventilation system to control gas outbursts and prevent gas exceedances. However, this method involves high initial investment, long operating cycles, and poor economic returns. The vast majority of coalfields in my country consist of low-permeability coal seams. Various coal seam fracturing and permeability enhancement technologies have been proposed domestically, such as hydraulic fracturing, electric pulse shock waves, high-pressure air blasting, and carbon dioxide blasting. These technologies have achieved good application demonstrations in areas such as coal mine gas outburst control, coalfield gas management, and coalbed methane extraction. However, these technologies still face numerous challenges in terms of applicability, economics, and safety.

[0003] Ultrasonic waves are mechanical waves with strong penetrating power. They can exert cavitation and mechanical effects on coal seams, accompanied by thermal and chemical effects, accelerating the separation and diffusion of methane molecules from the coal matrix. Chinese invention patent CN109707435B discloses a system and method for improving coal seam gas extraction using a combination of acoustic field and hydraulic fracturing technology. This method applies an ultrasonic field after hydraulic fracturing to promote gas extraction, offering advantages in terms of technical applicability, economy, and safety. However, methods for real-time monitoring in mines to determine whether ultrasonic waves improve coal seam permeability and gas extraction efficiency remain unreported. Therefore, a method is urgently needed to comprehensively monitor the permeability enhancement effect of ultrasonic waves and evaluate its impact on gas extraction efficiency. Summary of the Invention

[0004] The purpose of this 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 on coal seam permeability enhancement and the change in gas extraction efficiency under ultrasonic permeability enhancement by comprehensively monitoring multi-dimensional indicators such as ultrasonic parameters, coal structure changes, and gas extraction data.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring includes the following steps:

[0007] Step 1: Monitor the operating status of the ultrasonic generator in ultrasonic enhanced gas extraction in real time.

[0008] Step 2: Monitor the state of the target coal body; monitor the structural changes, stress distribution, gas concentration, and microseismic events of the target coal body in real time, and evaluate the physical changes and gas release of the target coal body under the action of the ultrasonic wave field;

[0009] Step 3: Monitor the gas drainage state, 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 to evaluate whether ultrasonic permeability enhancement is effective for gas drainage; if effective, track and monitor the rate of change of the gas drainage efficiency W1 with time W2 to evaluate the persistence of the ultrasonic permeability enhancement effect;

[0010] 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 volume; q represents the gas concentration before drainage;

[0011] Step 4: Calculate the gas drainage efficiency improvement rate W3 to evaluate the ultrasonic permeability enhancement effect;

[0012] ;

[0013] 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 occurring per unit time;

[0014] 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.

[0015] 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.

[0016] Furthermore, the state of the target coal body in Step 2 includes coal body permeability, fracture line density, internal stress, gas concentration, and microseismic events.

[0017] Furthermore, images of the interior of the target coal seam are captured by a digital panoramic borehole camera, and structural changes are obtained 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.

[0018] Furthermore, in step 4, the gas extraction efficiency W1 needs to be tracked and monitored for at least three months.

[0019] The beneficial effects of this invention are as follows: By comprehensively monitoring the ultrasonic penetration enhancement effect through multiple methods, a comprehensive assessment of the improvement in gas drainage efficiency is achieved. First, by monitoring the parameters of the ultrasonic generator, the stable operation of the ultrasonic waves according to the set parameters is ensured. Second, by monitoring the coal body structure, stress distribution, gas concentration, and microseismic events, the physical changes of the target coal body and gas release under the action of the ultrasonic field are assessed. Then, by monitoring the gas drainage flow rate and concentration, the gas drainage efficiency is calculated, and the impact of ultrasonic penetration enhancement on the gas drainage effect is assessed. Next, by long-term tracking and monitoring the rate of change in gas drainage efficiency, the persistence of the ultrasonic penetration enhancement effect is assessed. Finally, by calculating the gas drainage efficiency improvement rate, a judgment standard is established to comprehensively evaluate the improvement effect of ultrasonic penetration enhancement on gas drainage efficiency. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the process of the present invention.

[0021] Figure 2 shows the real-time recorded data of gas extraction efficiency W1 changing over time.

[0022] Figure 3 is a schematic diagram of the time series database of the change rate of gas extraction efficiency W2. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] As shown in Figure 1, this embodiment discloses a method for evaluating the ultrasonic permeability enhancement effect of coal seams based on multi-parameter joint monitoring, which includes the following steps:

[0025] Step 1: Monitor the operating status of the ultrasonic generator;

[0026] This embodiment is based on ultrasonic field enhanced gas extraction technology. Therefore, it is necessary to monitor the operating status of the ultrasonic generator in ultrasonic enhanced 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 (°). Monitoring the real-time changes of the operating status parameters ensures that the ultrasonic can operate stably and provides benchmark data for subsequent effect evaluation.

[0027] Step 2: Monitor the condition of the target coal seam;

[0028] The structural changes, stress distribution, gas concentration, and microseismic events of the target coal body are monitored in real time to assess the physical changes and gas release under the action of an ultrasonic field. The target coal body condition data includes coal permeability (mD), crack linear density (cracks / m), internal stress (stress magnitude and direction), gas concentration (%), and microseismic events (number of occurrences) to assess the physical changes and gas release of the target coal body under the action of an ultrasonic field.

[0029] To monitor the condition of the target coal seam, the technical means employed 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 captures images of the interior of the target coal seam, and the structural changes are obtained 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.

[0030] Step 3: Monitor the gas extraction status;

[0031] The gas extraction process was monitored, and the gas extraction efficiency W1 was calculated based on the monitoring data to evaluate the impact of ultrasonic field permeability enhancement on the gas extraction effect.

[0032] Monitoring data during gas drainage include gas drainage flow rate c (m³ / h), gas drainage concentration v (%), gas drainage time t (h), coal seam resource quantity m (t), and gas concentration q (m³ / t) before drainage.

[0033] 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 quantity; and q represents the gas concentration before extraction.

[0034] Step 4: Monitor the rate of change of gas extraction efficiency W1 over time;

[0035] After the ultrasonic permeability enhancement treatment, the gas drainage efficiency W1 is monitored for a long time, and the change rate of the gas drainage efficiency over time is recorded in real time to establish a time series database; to evaluate the persistence of the ultrasonic permeability enhancement effect.

[0036] The long-term tracking and monitoring time should be at least 3 months. The calculation model of the change rate W2 of the gas drainage efficiency over time is as follows: ; where [[ID= six]] represents the gas drainage efficiency in the current time period; is the gas drainage efficiency in the previous time period.

[0037] Based on the change rate W2 of the gas drainage efficiency before and after the ultrasonic permeability enhancement treatment, the persistence of the ultrasonic permeability enhancement effect is evaluated.

[0038] Step 5: Calculate the gas drainage efficiency improvement rate W3, and establish a discrimination criterion for comprehensively monitoring by various means whether the ultrasonic cavitation effect can improve the gas drainage efficiency.

[0039] If the change rate Q of the gas concentration is less than 0.1%, it is regarded as the failure of ultrasonic permeability enhancement, and the gas drainage efficiency improvement rate, W3 = 0.

[0040] If the change rate Q of the gas concentration is greater than or equal to 0.1%, the calculation formula of W3 is as follows,

[0041] [[ID=twenty-four]] ;

[0042] Combined with the index requirements of the gas drainage time and the gas drainage compliance time, 0 < W3 ≤ 1.2, based on the ultrasonic cavitation effect, the gas drainage efficiency can be improved, 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.

[0043] Taking the use of ultrasonic permeability enhancement and coal seam gas drainage before coal mine exploitation as an example to verify the effectiveness of this embodiment.

[0044] (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.

[0045] (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.

[0046] (3) Calculate the gas drainage efficiency W1: Before ultrasonic permeability enhancement, W 1t1 is 20%, after ultrasonic permeability enhancement, W1t2 It is increased to 30%, and the tracking and monitoring are shown in Figure 2.

[0047] (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 shown in Figure 3.

[0048] (5)Calculate the improvement rate of gas drainage efficiency .

[0049] (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 the gas drainage efficiency.

[0050] As mentioned above, it is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope 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, The process includes the following steps: Step 1: Real-time monitoring of the operation status of the ultrasonic generator in ultrasonic enhanced gas extraction; Step 2: Monitoring the target coal body condition; real-time monitoring of structural changes, stress distribution, gas concentration, and microseismic events in the target coal body, and evaluating the physical changes and gas release under ultrasonic action; Step 3: Monitoring the gas extraction status of the coal seam, and calculating the gas extraction efficiency W1 based on the monitoring data, calculating the gas extraction efficiency before and after ultrasonic enhancement of the coal seam to evaluate whether ultrasonic enhancement is effective in improving gas extraction efficiency; if ultrasonic enhancement is effective in gas extraction, tracking and monitoring the rate of change W2 of the gas extraction efficiency W1 over time to evaluate the durability 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 quantity; q represents the gas concentration before extraction; Step 4: Calculate the gas extraction efficiency improvement rate W3 to evaluate the ultrasonic permeability enhancement effect. Where 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; and P is the output power of the ultrasonic generator. For a step function, when x is a specific ultrasonic frequency Otherwise, it is 0; K t1 K represents the coal permeability at time t1. t2 t2 represents the coal permeability; Tex represents the fracture linear density; S represents the number of microseismic events per unit time. This represents the gas extraction efficiency for the current time period. It is the gas drainage efficiency in the previous time period. When 0 < W3 ≤ 1.2, the ultrasonic wave permeability enhancement effect is poor; when 1.2 < W3 ≤ 2.5, the ultrasonic wave permeability enhancement effect is medium; when 2.5 < W3 ≤ 3.7, the ultrasonic wave permeability enhancement effect is good; when 3.7 < W3, the ultrasonic wave permeability 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, In step 1, the operating status of the ultrasonic generator includes output power, ultrasonic frequency, ultrasonic pulse width, ultrasonic amplitude, action time, and emission angle; real-time changes in operating status parameters are monitored to achieve stable operation of the ultrasonic generator.

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 body condition in step 2 includes coal permeability, fracture linear 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, characterized in that, Images of the interior of the target coal seam are captured by a digital panoramic borehole camera, and structural changes are obtained by analyzing the image information; a distributed fiber optic sensing system is used to monitor internal stress; a methane detector is used to monitor gas concentration; and a 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, the gas extraction efficiency W1 needs to be tracked and monitored for at least three months.

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