A combined monitoring system and method for microseismic and stress monitoring of hydraulic fracturing in coal mines

Abstract

This invention relates to a combined monitoring system for microseismic and stress conditions in underground hydraulic fracturing in coal mines, belonging to the field of wireless communication technology. The system includes the following steps: a data acquisition module deployed at the underground fracturing operation site in the coal mine to acquire on-site physical field data; a data transmission module connected to the data acquisition module to convert the acquired physical field data using a protocol and transmit it; and a central processing module connected to the data transmission module to receive and analyze the data, generating a comprehensive evaluation index for fracturing effectiveness based on the spatial concentration of microseismic events and the decreasing gradient of stress data. A supporting method for combined monitoring of microseismic and stress conditions in underground hydraulic fracturing in coal mines is also provided.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology and relates to a combined monitoring system and method for microseismic and stress monitoring of hydraulic fracturing in coal mines. Background Technology

[0002] In underground coal mining, the presence of hard roofs or hard coal seams is one of the main factors restricting safe and efficient production. Hard roofs are difficult to collapse naturally, easily forming large-area overhangs in goaf areas, leading to the accumulation of a large amount of elastic energy. Once they suddenly fracture, they can easily induce strong mine pressure manifestations or even rockburst dynamic disasters. At the same time, hard coal seams are often accompanied by poor permeability and difficulties in gas extraction. Therefore, underground directional hydraulic fracturing technology, as an active means of weakening rock strata and increasing permeability, has been widely used in coal mine rockburst prevention, hard roof control, and gas management projects. However, current evaluation methods for fracturing effectiveness have significant limitations.

[0003] Existing monitoring systems are mostly stand-alone hardware devices. While microseismic monitoring systems can locate cracks, they cannot directly reflect the degree of stress release in the rock mass; stress monitoring systems can visually reflect the pressure relief effect, but their "point" monitoring cannot reveal the overall spatial morphology of the cracks.

[0004] Furthermore, existing technologies lack a modular system architecture, making it impossible to effectively integrate and analyze heterogeneous data from different sources, such as high-frequency microseismic waveform data and low-frequency stress change data. This makes it difficult for on-site engineers to accurately determine whether fracturing operations meet standards in real time, often resulting in "blind fracturing" or "ineffective fracturing." Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a combined monitoring system and method for hydraulic fracturing microseismic and stress monitoring in coal mines. Through modular design, it realizes the fusion analysis of multi-source data, solving the problems of single evaluation methods and low data utilization in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A combined microseismic and stress monitoring system for hydraulic fracturing in coal mines includes the following steps: A data acquisition module is deployed at the underground fracturing operation site in a coal mine to acquire on-site physical field data. The data acquisition module includes a microseismic monitoring unit, a stress monitoring unit, and a fracturing condition monitoring unit. The microseismic monitoring unit is used to acquire elastic wave signals generated by rock mass fracturing. The stress monitoring unit is used to acquire vertical stress data within the rock mass. The fracturing condition monitoring unit is used to monitor the outlet pressure and cumulative water injection volume of the water injection pump station in real time and sends the condition data to the joint evaluation unit as auxiliary evaluation parameters. The data transmission module, connected to the data acquisition module, is used to convert the acquired physical field data according to the protocol and transmit it. The central processing module, connected to the data transmission module, is used to receive and analyze data, and generate a comprehensive evaluation index of fracturing effect based on the spatial concentration of microseismic events and the decreasing gradient of stress data. The central processing module includes a data synchronization unit, a feature extraction unit, and a joint evaluation unit. The data synchronization unit is used to perform timestamp calibration on the data streams of the microseismic monitoring unit and the stress monitoring unit to ensure the consistency of the two types of data on the time axis. The feature extraction unit is used to extract the features of the two types of data. The joint evaluation unit is used to generate a comprehensive evaluation index of fracturing effect based on the spatial clustering of microseismic events and the decreasing gradient of stress data.

[0007] Furthermore, the microseismic monitoring unit includes a microseismic sensor array arranged around the fracturing borehole; the stress monitoring unit includes a borehole stress gauge installed at the depth of a preset monitoring hole; and the fracturing condition monitoring unit is installed at the outlet of the water injection pump station and is electrically connected to the joint evaluation unit.

[0008] Furthermore, the central processing module also includes a three-dimensional visualization interaction unit, which is used to construct a three-dimensional geological model of the target coal and rock strata and to overlay and display the microseismic event point cloud and stress change cloud map on the three-dimensional geological model.

[0009] On the other hand, the present invention provides a method for combined monitoring of microseismic vibration and stress in underground hydraulic fracturing in coal mines, based on the above-mentioned system, including the following steps: S1: System initialization, deploying a data acquisition module in the fracturing area and establishing a connection with the central processing module through the data transmission module; S2: Background value acquisition, using the data acquisition module to collect background microseismic noise and initial rock stress values ​​before fracturing; S3: Synchronous monitoring. During hydraulic fracturing operations, the data synchronization unit receives microseismic waveform data and stress flow data in real time. S4: Feature calculation, the feature extraction unit performs location calculation on the microseismic data to obtain the spatial location of the crack, and performs filtering processing on the stress data to obtain the stress change rate; S5: Joint evaluation. The joint evaluation unit determines whether the microseismic event covers the stress monitoring point area and detects whether the stress value in the area has a stress relief response. S6: Feedback control, outputting fracturing construction adjustment instructions based on joint evaluation results.

[0010] Furthermore, in step S3, the fracturing pump is started, and the system enters the real-time working state data synchronization unit to ensure that the micro-vibration waveform and stress curve are strictly corresponding on the time axis.

[0011] Furthermore, the joint evaluation logic in step S5 is as follows: when the microseismic event extends spatially to the radius R of the installation location of the stress monitoring unit, and the stress value monitored by the corresponding stress monitoring unit decreases by more than the threshold Δσ, the fracturing in the area is deemed effective; otherwise, the crack in the area is deemed not to be connected or the pressure relief is insufficient.

[0012] Furthermore, the fracturing operation adjustment instructions output in step S6 include: increasing water injection pressure, extending pressure holding time, or changing the hole spacing of the fracturing boreholes in the next stage.

[0013] The beneficial effects of this invention are as follows: the combined microseismic and stress monitoring system and method for hydraulic fracturing in coal mines breaks down the complex monitoring task into three core modules: acquisition, transmission, and processing. The system uses a microseismic monitoring unit to "track" the crack trajectory, a stress monitoring unit to "quantify" the decompression amplitude, and a central processing module to "overlay" the two in the spatiotemporal dimension. This modular system not only improves the accuracy of monitoring data but also greatly enhances the system's scalability and maintenance efficiency, providing a scientific basis for optimizing hydraulic fracturing parameters in coal mines.

[0014] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 A framework diagram of a combined microseismic and stress monitoring system for hydraulic fracturing in coal mines; Figure 2 This is a structural diagram of the combined monitoring system for hydraulic fracturing microseismic vibration and stress in coal mines.

[0016] Figure reference numerals: 100-Data acquisition module, 110-Microseismic monitoring unit, 120-Stress monitoring unit, 130-Fracturing condition monitoring unit, 200-Data transmission module, 300-Central processing module, 310-Data synchronization unit, 320-Feature extraction unit, 330-Joint evaluation unit, 340-3D visualization interaction unit. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0018] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0019] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0020] Example 1: like Figure 1-2 As shown, this invention provides a combined monitoring system for microseismic vibration and stress in underground hydraulic fracturing in coal mines, comprising: The data acquisition module 100 is deployed at the fracturing operation site in the coal mine to acquire on-site physical field data. The data acquisition module 100 includes a microseismic monitoring unit 110, a stress monitoring unit 120, and a fracturing condition monitoring unit 130. The microseismic monitoring unit 110 includes a microseismic sensor array centered on the fracturing borehole to collect elastic wave signals generated by rock fracturing. The stress monitoring unit 120 includes a borehole stress gauge installed at the depth of a preset monitoring hole to collect vertical stress data inside the rock mass. The fracturing condition monitoring unit 130 is used to monitor the outlet pressure and cumulative water injection volume of the water injection pump station in real time and sends the condition data to the joint evaluation unit 330 as auxiliary evaluation parameters. The data transmission module 200 is connected to the data acquisition module 100 and is used to convert the acquired physical field data into protocols and transmit it. The central processing module 300, connected to the data transmission module 200, is used to receive and analyze data. The central processing module 300 includes a data synchronization unit 310, a feature extraction unit 320, and a joint evaluation unit 330. The data synchronization unit 310 is used to perform timestamp calibration on the data streams of the microseismic monitoring unit 110 and the stress monitoring unit 120 to ensure the consistency of the two types of data on the time axis. The joint evaluation unit 330 is configured to generate a comprehensive evaluation index of fracturing effect based on the spatial clustering of microseismic events and the decreasing gradient of stress data. The central processing module 300 also includes a three-dimensional visualization interaction unit 340, which is used to construct a three-dimensional geological model of the target coal and rock strata and to overlay the microseismic event point cloud and stress change cloud map on the three-dimensional geological model.

[0021] Example 2: A method for combined microseismic and stress monitoring of hydraulic fracturing in coal mines includes the following steps: S1: System initialization, deploy data acquisition module 100 in the fracturing area and establish connection with central processing module 300 through data transmission module 200; install sensor units in fracturing holes and monitoring holes in the roadway and complete module power-on self-test; S2: Background value acquisition: The background microseismic noise and initial rock stress value before fracturing are collected using the data acquisition module 100. Before water injection, the system runs for more than 24 hours to obtain the environmental microseismic noise level and the initial stress balance value of the rock layer, which will serve as the benchmark for subsequent comparison. S3: Synchronous monitoring. During hydraulic fracturing operations, the data synchronization unit 310 receives microseismic waveform data and stress flow data in real time; upon starting the fracturing pump, the system enters real-time operating mode. The data synchronization unit 310 ensures that the microseismic waveform and stress curve are strictly correlated on the time axis. S4: Feature Calculation. The feature extraction unit 320 performs location calculations on the microseismic data to obtain the spatial location of the cracks and filters the stress data to obtain the stress change rate. For example, it calculates that "at 10:05:01, a crack with an energy of 1000J occurred at coordinates (100, 20, 50)". Simultaneously, it detects that "at 10:05:05, the stress gauge reading at a distance of 5 meters from the aforementioned coordinates decreased from 15MPa to 12MPa". S5: Joint evaluation. The joint evaluation unit 330 determines whether the microseismic event covers the stress monitoring point area and detects whether the stress value in that area has undergone a pressure relief response. Based on the results of step S4, the joint evaluation unit 330 makes a logical judgment: if the crack has extended to the monitoring area (microseismic evidence) and the rock mass has undergone substantial pressure relief (stress evidence), the conclusion is "fracturing effective". Conversely, if there is only microseismic activity without stress change, it indicates "crack not connected"; if there is only stress change without microseismic activity (less common, possibly due to equipment failure or creep), it indicates "data abnormality". S6: Feedback control, outputs fracturing construction adjustment instructions based on joint evaluation results, and decides whether to increase water injection pressure or change the spacing of the next borehole, thereby achieving refined construction; fracturing construction adjustment instructions include: increasing water injection pressure, extending pressure holding time or changing the hole spacing of the next stage of fracturing boreholes.

[0022] Based on the aforementioned modular system, this method achieves real-time closed-loop monitoring of fracturing crack propagation and stress relief response through steps such as data synchronization, feature calculation, and joint evaluation.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A combined monitoring system for microseismic vibration and stress in underground hydraulic fracturing in coal mines, characterized in that: Includes the following steps: A data acquisition module is deployed at the underground fracturing operation site in a coal mine to acquire on-site physical field data. The data acquisition module includes a microseismic monitoring unit, a stress monitoring unit, and a fracturing condition monitoring unit. The microseismic monitoring unit is used to acquire elastic wave signals generated by rock mass fracturing. The stress monitoring unit is used to acquire vertical stress data within the rock mass. The fracturing condition monitoring unit is used to monitor the outlet pressure and cumulative water injection volume of the water injection pump station in real time and sends the condition data to the joint evaluation unit as auxiliary evaluation parameters. The data transmission module, connected to the data acquisition module, is used to convert the acquired physical field data according to the protocol and transmit it. The central processing module, connected to the data transmission module, is used to receive and analyze data, and generate a comprehensive evaluation index of fracturing effect based on the spatial concentration of microseismic events and the decreasing gradient of stress data. The central processing module includes a data synchronization unit, a feature extraction unit, and a joint evaluation unit. The data synchronization unit is used to perform timestamp calibration on the data streams of the microseismic monitoring unit and the stress monitoring unit to ensure the consistency of the two types of data on the time axis. The feature extraction unit is used to extract the features of the two types of data. The joint evaluation unit is used to generate a comprehensive evaluation index of fracturing effect based on the spatial clustering of microseismic events and the decreasing gradient of stress data.

2. The combined monitoring system for hydraulic fracturing microseismic vibration and stress in coal mines according to claim 1, characterized in that: The microseismic monitoring unit includes a microseismic sensor array arranged around the fracturing borehole; the stress monitoring unit includes a borehole stress gauge installed at the depth of a preset monitoring hole; the fracturing condition monitoring unit is installed at the outlet of the water injection pump station and is electrically connected to the joint evaluation unit.

3. The combined monitoring system for hydraulic fracturing microseismic vibration and stress in coal mines according to claim 1, characterized in that: The central processing module also includes a three-dimensional visualization and interaction unit, which is used to construct a three-dimensional geological model of the target coal and rock strata and to overlay microseismic event point clouds and stress change cloud maps on the three-dimensional geological model.

4. A method for combined monitoring of microseismic vibration and stress in underground hydraulic fracturing in coal mines, characterized in that: The combined micro-vibration and stress monitoring system for hydraulic fracturing in coal mines according to any one of claims 1-3 includes the following steps: S1: System initialization, deploying a data acquisition module in the fracturing area and establishing a connection with the central processing module through the data transmission module; S2: Background value acquisition, using the data acquisition module to collect background microseismic noise and initial rock stress values ​​before fracturing; S3: Synchronous monitoring. During hydraulic fracturing operations, the data synchronization unit receives microseismic waveform data and stress flow data in real time. S4: Feature calculation, the feature extraction unit performs location calculation on the microseismic data to obtain the spatial location of the crack, and performs filtering processing on the stress data to obtain the stress change rate; S5: Joint evaluation. The joint evaluation unit determines whether the microseismic event covers the stress monitoring point area and detects whether the stress value in the area has a stress relief response. S6: Feedback control, outputting fracturing construction adjustment instructions based on joint evaluation results.

5. The method for combined monitoring of microseismic vibration and stress in underground hydraulic fracturing in coal mines according to claim 4, characterized in that: In step S3, the fracturing pump is started, and the system enters the real-time working status data synchronization unit to ensure that the micro-vibration waveform and stress curve are strictly corresponding on the time axis.

6. The method for combined monitoring of microseismic vibration and stress in underground hydraulic fracturing in coal mines according to claim 4, characterized in that: The joint evaluation logic in step S5 is as follows: when the microseismic event extends spatially to the radius R of the installation location of the stress monitoring unit, and the stress value monitored by the corresponding stress monitoring unit decreases by more than the threshold Δσ, the fracturing in the area is deemed effective; otherwise, the crack in the area is deemed not to be connected or the pressure relief is insufficient.

7. The method for combined monitoring of microseismic vibration and stress in underground hydraulic fracturing in coal mines according to claim 4, characterized in that: The fracturing operation adjustment instructions output in step S6 include: increasing water injection pressure, extending pressure holding time, or changing the hole spacing of the fracturing boreholes in the next stage.

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