Research On Monitoring Technology And Application Of Borehole Collapse Based On Fiber Grating

Coal seam occurrence conditions in China are complex and changeable,and gas disasters are serious.Affected by the in-situ stress,the boreholes of mine gas drainage are prone to collapse and deformation,which seriously affects the gas control effect.However,at this stage,there are few monitoring methods for borehole collapse,and targeted borehole repair cannot be carried out.Based on this background,this paper uses fiber grating sensing technology to monitor the collapse of boreholes.By consulting a large number of documents,on the basis of previous research,comprehensively adopt theoretical analysis,collapse hole characterization experiments,physical similarity simulation experiments,The research method combined with field test is used to research the technology and application of fiber grating hole collapse monitoring technology.The main research work of this paper is as follows.(1)Fiber Bragg gratings can monitor physical quantities such as temperature and stress by measuring the wavelength shift.The grating packaging method selected in this paper is surface-mounted.By constructing the strain analysis model of the fiber grating,the adhesive layer and the matrix material,the strain transfer efficiency formula from the matrix material to the fiber grating measuring point in the practical application of the surface-mounted fiber grating sensor is solved,which lays a theoretical foundation for the measurement of the experimental parameters.The amount of coal slumped in the borehole can be characterized by measuring the wavelength shift of the grating,and the approximate position of the slumped hole can be determined according to the location of the grating measuring points.(2)The characterization experiment of borehole collapse is designed,and the coal sample obtained from the air inlet road of the 2802 working face of Zhangcun Coal Mine is simply broken and used to simulate the real collapsed coal body shape in the borehole.Three groups of tests were set,and the fiber grating measuring points were deflected by 0°,90° and 180°,respectively.By simulating the hole collapse in the borehole,the linear relationship between the amount of coal collapse and the wavelength offset of each group was obtained.(3)Considering the protection of grating measuring points and the accuracy of monitoring data,based on the experimental data of hole collapse characterization,the corresponding relationship between the grating measurement wavelength offset and the amount of collapsed coal and the extraction flow is constructed.The attenuation ratio of extraction flow is used as the evaluation standard of hole collapse,and the measurement wavelength offset is used to characterize the amount of collapsed coal.The severity of hole collapse is divided into three levels:Level Ⅰ collapsed hole drainage flow attenuation is less than 10%,the wavelength shift of grating measurement is less than 19.6pm,and the amount of collapsed coal is at least 59.2g;Level Ⅱ slump drainage flow attenuation is between 10%-50%,grating measurement wavelength offset is between 19.6-99.8pm,and slump coal amount is between 59.2301.4g;Level Ⅲ collapsed hole drainage attenuation is greater than 50%,the wavelength shift of grating measurement is greater than 99.8pm,and the amount of collapsed coal is at least 301.4g.(4)Build a physical similarity simulation experiment,arrange grating measuring points and acoustic emission sensors,and monitor the collapse of the borehole and the development of cracks around the hole.In the case of stress loading,comparing the sudden change of wavelength offset measured by grating at each measuring point and the surge segment of acoustic emission detection data can basically correspond one-to-one,which verifies the accuracy of fiber grating in monitoring the position of collapsed holes.(5)In the 2802 working face of Zhangcun Coal Mine,5 boreholes were selected to carry out the field test of hole collapse monitoring technology,and the situation of hole collapse and drilling data were continuously monitored for 30 days.After the drilling is completed,among the monitored boreholes,the No.2 and No.5 boreholes have better hole forming effect and can maintain a good gas drainage efficiency for a long time;the No.1,No.3 and No.4 hole collapsed immediately after the drilling was withdrawn.The level of the collapsed hole was close to the third-level collapsed hole,and after the completion of the one-month extraction work,the collapsed hole became more serious,which seriously affected the drilling effect.According to the different hole collapse conditions and different hole depths of the monitoring hole,a targeted hole repair plan is proposed.Comprehensive statistics and monitoring of the drainage data before and after the repair of the boreholes show that the extraction purities of the boreholes are increased by 14.5%after adopting the appropriate repairing technology of the boreholes,and the effect of the repairing of the boreholes is obvious.Through the field test effect test,the monitoring results of the collapsed hole can provide effective theoretical guidance for the failure repair of the gas drainage hole,and effectively solve the problem of monitoring the collapsed hole after the hole is drilled.The monitoring of the position of the collapsed hole and the amount of collapsed coal has been realized,which has great practical significance for the repair of the failure of the drilling and the precise support of the section of the easily collapsed hole in the drilling.