Comparative Analysis of the Drainage Effect Based on Improved Hydraulic Flushing Technology

Abstract

The composite structure coal seam composed of coal seams with strong and weak deformation is widely developed in the coalfields in Southwest and North China. The implementation of hydraulic flushing in soft coal stratification can effectively relieve the pressure and increase the permeability of coal seams, so it can improve the effect of underground gas drainage. Taking Xin'an Coal Mine, West Henan province, China, as an example, this paper discussed the influence of hydraulic flushing on the gas drainage effect in soft coal seam by means of field investigation, numerical simulation analysis, similar simulation, and field verification. As the same time, a fluid−solid coupling model of gas drainage based on layered hydraulic flushing technology is established, and the differences and reasons of the gas drainage effect after layered hydraulic flushing in soft and hard composite coal seams are discussed. The results show that (1) the gas concentration change of layered flushing boreholes intermittently rises rapidly, and there is no obvious law, while that of conventional flushing boreholes shows a regular attenuation trend. (2) According to the numerical simulation results, after 30 days of drainage, the effective drainage range of layered hydraulic flushing is 8.33 m 3 higher than that of conventional hydraulic flushing. (3) There are not a few points where the single borehole concentration data of each row of layered flushing boreholes are in the high level. Meanwhile, the maximum concentration of all conventional flushing boreholes is less than 40%, except that one borehole can reach 70% at the beginning. (4) All of the average gas drainage concentration of single-row boreholes using layered flushing technology is greater than 20% in the vast majority of days, while that of the conventional flushing boreholes is only higher than 20% in row 5 and has only lasted for 2 days. The difference of the drainage effect is obvious.

Study on the Application of Comprehensive Gas Control Technology for Source-Separated Three-Dimensional Gas Extraction in Large Mining Faces

“…Zhang 13 and Huijun 14 Studied the effect of high-level borehole gas extraction technology on the management of gas in goaf area. In order to manage the gas in soft and hard composite coal seams, Li 15 researched that the construction of high-pressure water jet hydraulic flushing technology in the floor drainage roadway can improve the effect of gas extraction. Zhang 16 studied the synergistic management technology of gas and coal spontaneous combustion in stratified mining of thick coal seams.…”

Study on the Effect of Strain-Softening on Permeability and Gas Pressure in Surrounding Rocks of a Hydraulic Flushing Borehole

“…Zhang et al conducted a systematic study on developing hydraulic flushing technology and equipment in China . Li et al discussed the impact of hydraulic flushing on gas drainage efficiency in soft coal seams …”

“…26 Li et al discussed the impact of hydraulic flushing on gas drainage efficiency in soft coal seams. 27 Most of the above studies have been conducted using the Mohr−Coulomb model, without considering the strain-softening of borehole surrounding rocks. [21][22][23]27 The stress redistribution after formation of a borehole can change the permeability of the surrounding rocks of the borehole, which can affect the gas flow near the borehole.…”

“… 26 Li et al discussed the impact of hydraulic flushing on gas drainage efficiency in soft coal seams. 27 …”

“…Most of the above studies have been conducted using the Mohr–Coulomb model, without considering the strain-softening of borehole surrounding rocks. − , The stress redistribution after formation of a borehole can change the permeability of the surrounding rocks of the borehole, which can affect the gas flow near the borehole. − Ignoring the strain-softening of the surrounding rock of the borehole can impact the research results of hydraulic flushing gas extraction. A comparison between the Mohr–Coulomb model and the strain-softening model is shown in Figure (σ is the stress, ε is the strain).…”