METHOD FOR BEDDING PRECISE PRESSURIZED WATER INJECTION BASED ON COAL SEAM INTERVAL HYDRAULIC GRADIENT CALCULATION

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Application No. 202410610239.4, filed on May 16, 2024, entitled “METHOD FOR BEDDING PRECISE PRESSURIZED WATER INJECTION BASED ON COAL SEAM INTERVAL HYDRAULIC GRADIENT CALCULATION”. These contents are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to the technical field of mine disaster prevention, in particular to a method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation.

BACKGROUND

Coal is currently one of the most abundant, widely distributed, and economically used energy resources in the world. Coal resources have long been the most important basic energy and industrial raw materials, making significant contributions to ensuring national energy security and stable socio-economic development. However, with the increasing depth and intensity of coal mining in China, significant changes have occurred in coal structure, coal seam temperature, and ground stress. The risk of high concentration dust in mines causing disasters is becoming increasingly high, which seriously affects the safe and efficient production of coal. As the coal seam water injection technology can significantly reduce the coal body ground stress, and at the same time increase the water content to inhibit the generation of coal dust, so the coal seam water injection technology has become a commonly used source dust reduction method in most mining areas in China. However, during the implementation of coal seam water injection on site, there are challenges such as difficulty in effectively cracking with low-pressure water injection and water flooding caused by high-pressure water injection, which will limit the dust reduction effect of coal seam water injection on site.

At present, in order to avoid the impact of water flooding on the disaster prevention effect of coal seam water injection in existing technology, a stable pressure water injection system is usually used to stabilize the water injection pressure. The present disclosure provides a new method that achieves precise pressure control during coal seam water injection without the need for a stable pressure water injection system.

SUMMARY

The present disclosure provides a method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation. The method is different from the existing technology, which overcomes the defects of the existing technology that the water injection pressure is difficult to be effectively controlled. The method of the present disclosure can meet the needs of different mines to carry out the coal seam bedding water injection disaster prevention operation, providing scientific guidance for improving the effectiveness of coal seam water injection disaster prevention.

The technical solution of the present disclosure is as follows:

A method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation includes the following steps:

• • Step 1, based on the on-site basic data that the effective water invasion influence radius of a coal seam bedding water injection process is within 5 meters, constructing two pressure measurement boreholes on both sides of a water injection borehole with the water injection borehole as a center, respectively; distances between the two pressure measurement boreholes on the left side and the water injection borehole is 2 meters and 4 meters respectively, and distances between the two pressure measurement boreholes on the right side and the water injection borehole is 3 meters and 5 meters respectively;
  • Step 2, sealing the water injection borehole with two-plugging and one-injection; then, performing cement grouting to seal each pressure measurement borehole, and monitoring the stress changes inside each pressure measurement borehole through a monitoring device;
  • Step 3, recording an initial pressure value in each pressure measurement borehole before injecting water into coal seams, and then start injecting water; obtaining real time pressure changes in the water injection boreholes and each pressure measurement borehole during the coal seam water injection process, and conducting timing of pressure change nodes at different positions of the pressure measurement boreholes; based on the pressure difference and distance between the water injection borehole and the pressure measurement boreholes, and the difference between the initial pressure inside the pressure measurement boreholes and the pressure when the pressure inside the pressure measurement boreholes reach stable after the start of water injection, calculating the hydraulic gradient during the water injection process to obtain the dynamic damage of pressure water along the path;
  • Step 4, based on the pressure difference changes within different water injection radius ranges and the pressure change nodes of the pressure measurement boreholes, increasing the coal seam water injection pressure in a timely manner at the corresponding time nodes during the coal seam water injection process in the same coal seam.

In step 2 of the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation mentioned above, the sealing length of the water injection borehole is the length other than the distance that is not less than 5 meters from the borehole orifice to the borehole bottom of the water injection borehole; the sealing length of each pressure measurement borehole is within 10 meters from the borehole bottom of each pressure measurement borehole.

In the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation mentioned above, the monitoring device includes stress-strain gauges and stress display instruments, stress display instruments are located near the borehole orifice of each pressure measurement borehole, stress-strain gauges are arranged in each pressure measurement borehole, and the stress-strain gauges transmit the stress changes in each pressure measurement borehole to the stress display instruments.

In step 1 of the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation mentioned above, the construction position of the borehole bottom of each pressure measurement borehole is 5 meters deeper than the construction position of the borehole bottom of the water injection borehole.

In step 4 of the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation mentioned above, increasing the coal seam water injection pressure is used to avoid the phenomenon of water flooding caused by excessive initial water injection pressure, and used to compensate for dynamic damage of the pressurized water.

In the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation mentioned above, the stress-strain gauges are pasted in each pressure measurement borehole.

Compared with the existing technology, the present disclosure brings the following advantageous technical effects:

• • 1. In the construction process of coal seam water injection drilling and pressure measurement borehole, the method provided by the present disclosure selects the water injection borehole as the center, and arranges two pressure measurement boreholes on both sides of the water injection borehole. The distance between the pressure measurement borehole located at one side and the water injection borehole is 2 meters and 4 meters, and the distance between the pressure measurement borehole located at the other side and the water injection borehole is 3 meters and 5 meters. Based on the on-site basic data indicating that the effective water infusion influence radius of the coal seam water injection process along the seam is all within 5 meters, the spacing between the water injection borehole and the pressure measurement boreholes are set at 2 meters, 3 meters, 4 meters, and 5 meters respectively.” Compared with the existing technology, this construction method can effectively reduce the construction workload and efficiently calculate the coal seam water injection pressure.
  • 2. The method provided by the present disclosure obtains real-time pressure changes in the water injection borehole and pressure measurement boreholes during the coal seam water injection process, and timing the pressure change nodes at different positions of the pressure measurement boreholes. Based on the pressure difference between the water injection borehole and the pressure measurement boreholes at different distances, the along-the-path dynamic damage of the pressurized water is calculated, and the measurement method is simple and easy to implement.
  • 3. During the coal seam water injection process, based on the pressure change inside the pressure measurement boreholes—the distance curve between the pressure measurement boreholes and the water injection borehole, and the water injection time, the method provided by the present disclosure adjusts the water injection pressure at corresponding time points, this can compensate for the hydrodynamic damage caused by pressure to a certain extent, further improve the wetting radius of coal seam water injection, thereby providing technical guidance for improving the disaster prevention effect of coal seam water injection. At the same time, it reduces the power and energy losses during the coal seam water injection process and promotes sustainable development.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the construction layout of coal seam water injection borehole and pressure measurement boreholes according to the present disclosure;

FIG. 2 shows the principle diagram of bedding precise pressurized water injection.

The reference marks in the figures, 1—coal seam, 2—pressure measurement borehole, 3—two-plugging and one—injection sealing hole, 4—water injection borehole, 5—cement grouting sealing hole.

DETAILED DESCRIPTION OF THE EMBODIMENT

In order to make the technical problems, technical solutions and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

As shown in FIG. 1, the construction layout of the coal seam water injection borehole and pressure measurement boreholes of the present disclosure is illustrated. The figure shows coal seam 1, pressure measurement borehole 2, two-plugging and one-injection sealing hole 3, water injection borehole 4, and cement injection sealing hole 5, respectively. In terms of the layout of the water injection borehole and the pressure measurement boreholes, the present disclosure has made improvements. Based on the on-site basic data that the effective water invasion influence radius of the coal seam water injection process is within 5 meters, two pressure measurement boreholes are arranged on both sides of the water injection borehole with the water injection borehole as the center. The distance between the two pressure measurement boreholes on the left and the water injection borehole is 2 meters and 4 meters respectively, and the distance between the two pressure measurement boreholes on the right and the water injection borehole is 3 meters and 5 meters respectively. This design ensures that the spacing between the water injection borehole and the pressure measurement boreholes is 2 meters, 3 meters, 4 meters, and 5 meters respectively, further reducing the amount of construction work. In addition, the spacing design between the pressure measurement boreholes and the water injection borehole can lay the foundation for subsequent interval hydraulic gradient calculations.

Two-plugging and one-injection is used to seal the water injection borehole, and the sealing length of the water injection borehole is the length other than the distance that is not less than 5 meters from the borehole orifice to the borehole bottom of the water injection borehole. Cement injection is used to seal each pressure measurement borehole, and the sealing length of each pressure measurement borehole is within 10 meters from the borehole bottom of each pressure measurement borehole. Stress-strain gauges are installed inside each pressure measurement borehole. Specifically, the stress-strain gauges can be attached to the inner wall of the pressure measurement borehole, and a stress display instrument can be installed at the borehole orifice of each pressure measurement borehole. The stress-strain gauges are connected to the stress display instrument to observe the stress inside the pressure measurement borehole.

Afterwards, during the coal seam water injection process, the pressure changes in the water injection borehole and pressure measurement borehole can be obtained in real time through stress-strain gauges and stress display instruments. The pressure change nodes of pressure measurement boreholes at different positions (such as the two pressure measurement boreholes on the left side of the water injection borehole and the two pressure measurement boreholes on the right side of the water injection borehole) can be timed. Based on the pressure difference and distance between the water injection borehole and the pressure measurement boreholes, and the difference between the initial pressure inside the pressure measurement borehole and the pressure when the pressure inside the pressure measurement borehole reaches stable after the start of water injection, the hydraulic gradient during the water injection process can be calculated to obtain the dynamic damage of the pressure water along the path.

Finally, based on the pressure difference changes within different water injection radius ranges and the pressure change nodes of the pressure measurement boreholes, increasing the coal seam water injection pressure in a timely manner at the corresponding time nodes during the coal seam water injection process in the same coal seam. The method of the present disclosure can effectively avoid the phenomenon of water flooding caused by excessive initial pressure during water injection, and can also compensate for dynamic damage of the pressurized water to a certain extent, further improve the wetting radius of coal seam water injection, thereby providing technical guidance for improving the disaster prevention effect of coal seam water injection.

A method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation of the present disclosure will be described in detail as below, including the following steps:

• • Step 1, during the construction phase of the coal seam water injection drilling site, firstly, designing coal seam water injection boreholes, based on the on-site basic data that the effective water invasion influence radius of a coal seam bedding water injection process is within 5 meters, constructing pressure measurement boreholes on one side of the water injection borehole at intervals of 2 meters and 4 meters, and on the other side at intervals of 3 meters and 5 meters; the pressure measurement boreholes are equipped with stress-strain gauges, and the borehole orifice of each pressure measurement borehole is connected to a stress display instrument to achieve real-time measurement of internal stress in the borehole; and in order to further measure the water invasion situation in the annular area centered on the borehole bottom of the water injection borehole, the construction position of the borehole bottom of the pressure measurement borehole is designed to be 5 meters deeper than that of the water injection borehole;
  • Step 2, during the process of sealing borehole, sealing the water injection borehole with two-plugging and one-injection, and the sealing length of the water injection borehole is the length other than 5 meters from the borehole orifice to the borehole bottom of the water injection borehole; then, performing cement grouting to seal each pressure measurement borehole, the sealing length of each pressure measurement borehole is within 10 meters from the borehole bottom of each pressure measurement borehole, and and each pressure measurement borehole is equipped with stress-strain gauges and a stress display instrument connected to the borehole orifice to achieve real time measurement of internal stress in the borehole;
  • Step 3, obtaining real time pressure changes in the water injection boreholes and each pressure measurement borehole during the coal seam water injection process, and conducting timing of pressure change nodes at different positions of the pressure measurement boreholes; based on the pressure difference and distance between the water injection borehole and the pressure measurement boreholes, calculating the hydraulic gradient during the water injection process to obtain the dynamic damage of pressure water along the path;
  • Step 4, based on the pressure difference changes within different water injection radius ranges and the pressure change nodes of the pressure measurement boreholes, increasing the coal seam water injection pressure in a timely manner at the corresponding time nodes during the coal seam water injection process in the same coal seam. It can effectively avoid the phenomenon of water flooding caused by excessive initial pressure during water injection, and can also compensate for dynamic damage of the pressurized water to a certain extent, further improve the wetting radius of coal seam water injection, thereby providing technical guidance for improving the disaster prevention effect of coal seam water injection.

The present disclosure will be further explained in conjunction with specific embodiments.

Embodiment 1

Further explanation will be given on the application of the method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation in a certain mine.

The specific steps are as follows:

• • Step 1: during the construction phase of the coal seam water injection drilling site, first designing the coal seam water injection drilling holes; then, with the water injection drilling holes as the center, constructing pressure measurement boreholes at intervals of 2 meters and 4 meters on one side and 3 meters and 5 meters on the other side; further measuring the water invasion situation in the circular area centered on the borehole bottom of the water injection boreholes, setting the construction position of the borehole bottom of the pressure measurement borehole to be 5 meters deeper than that of the water injection borehole.
  • Step 2, during the process of sealing borehole, sealing the water injection borehole with two-plugging and one-injection, and the sealing length of the water injection borehole is the length other than 5 meters from the borehole orifice to the borehole bottom of the water injection borehole; then, performing cement grouting to seal each pressure measurement borehole, the sealing length of each pressure measurement borehole is within 10 meters from the borehole bottom of each pressure measurement borehole, and and each pressure measurement borehole is equipped with stress-strain gauges and a stress display instrument connected to the borehole orifice to achieve real time measurement of internal stress in the borehole.
  • Step 3, recording an initial pressure value in each pressure measurement borehole before injecting water into coal seams, and then start injecting water; obtaining real time pressure changes in the water injection boreholes and each pressure measurement borehole during the coal seam water injection process, and conducting timing of pressure change nodes at different positions of the pressure measurement boreholes; based on the pressure difference and distance between the water injection borehole and the pressure measurement boreholes, and the difference between the initial pressure inside the pressure measurement boreholes and the pressure when the pressure inside the pressure measurement boreholes reach stable after the start of water injection, calculating the hydraulic gradient during the water injection process to obtain the dynamic damage of pressure water along the path. As shown in FIG. 2, T represents the time from the start of water injection to the flow of water to each pressure measurement borehole, the vertical axis ΔP represents the difference between the initial pressure inside the pressure measurement borehole and the pressure when the pressure inside the pressure measurement borehole reaches stable after the start of water injection, and the horizontal axis represents the distance between the water injection borehole and the pressure measurement boreholes.
  • Step 4, based on the pressure difference changes within different water injection radius ranges and the pressure change nodes of the pressure measurement boreholes, increasing the coal seam water injection pressure in a timely manner at the corresponding time nodes during the coal seam water injection process in the same coal seam. As shown in FIG. 2, when the coal seam water injection time reaches T₁, the pressure change in the pressure measurement borehole 2 meters away from the water injection borehole is ΔP₁. At this time, the pressure of the coal seam water injection should be increased |ΔP₁|. When the coal seam water injection time reaches T₂, the pressure change in the pressure measurement borehole 3 meters away from the water injection borehole is ΔP₂, and the pressure of the coal seam water injection should be increased |ΔP₂|. When the coal seam water injection time reaches T₃, the pressure change in the pressure measurement borehole 4 meters away from the water injection borehole is ΔP₃, and the pressure of the coal seam water injection should be increased |ΔP₃|. When the coal seam water injection time reaches T₄, the pressure change in the pressure measurement borehole 5 meters away from the water injection borehole is ΔP₄, and the pressure of the coal seam water injection should be increased |ΔP₄|.

The calculation method of coal seam interval hydraulic gradient and the bedding precise pressurized water injection technology overcome the shortcomings of existing technologies such as difficult effective control of water injection pressure. The calculated data can provide reference for the coal seam water injection process under the same geological conditions, further improving the wetting radius of coal seam water injection, and providing technical guidance for improving the disaster prevention effect of coal seam water injection.

Certainly, the above descriptions are merely preferred embodiments of the present disclosure. The present disclosure is not limited to the above embodiments listed. It should be noted that, all equivalent replacements and obvious variations made by any person skilled in the art under the teaching of the specification fall within the essential scope of the specification and shall be protected by the present disclosure.