Method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation

Abstract

Provided is a method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation, including: setting pressure measurement boreholes on both sides of a water injection borehole with the water injection borehole as the center, and installing monitoring devices to measure internal stress of the pressure measurement boreholes in real time; during the coal seam water injection process, real-time pressure changes are obtained to determine the along-the-path dynamic damage of the pressurized water; according to the pressure difference changes within different water injection radius ranges and the pressure change nodes of the pressure measurement boreholes, during a water injection process in the same coal seam, the coal seam water injection pressure should be increased in a timely manner at the corresponding time nodes. The method of the present disclosure can effectively avoid the phenomenon of water flooding caused by excessive initial pressure during water injection.

What is claimed is: 
     
         1 . A method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation, comprising following steps in sequence:
 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 a left side and the water injection borehole is 2 meters and 4 meters respectively, and distances between the two pressure measurement boreholes on a 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.   
     
     
         2 . The method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation according to  claim 1 , wherein in step 2, 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. 
     
     
         3 . The method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation according to  claim 1 , wherein the monitoring device comprises 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. 
     
     
         4 . The method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation according to  claim 1 , wherein in step 1, 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. 
     
     
         5 . The method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation according to  claim 1 , wherein in step 4, 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. 
     
     
         6 . The method for bedding precise pressurized water injection based on coal seam interval hydraulic gradient calculation according to  claim 3 , wherein the stress-strain gauges are pasted in each the pressure measurement borehole.