Research and application of multi-channel gathering and conveying flower pipe with pressure resistance and hole protection in soft coal seam

WANG Zhenfeng; CAO Liangchao; LU Zhijie; WANG Feng; XIE Wenqiang; WEI Mintao; WANG Yonglong

doi:10.13225/j.cnki.jccs.2024.0462

Abstract：In response to the problem of instability collapse caused by pre-drainage borehole sealing after gas extraction in soft coal seams,leading to blockage or damage of reserved flower tubes and obstructing gas migration channels,severely affecting the gas treatment effect,a gathering flower tube for gas extraction in soft coal seams is studied.The structure comprises a gas extraction pipe,small flower tube,an extraction pipe-perforated pipe connector,an end connector,and a hole protection anti-blockage device.Through theoretical analysis,numerical simulation,and field experiments,the study analyzes the causes of flower tubes failure due to borehole instability and collapse.Using COMSOL and Fluent simula-tion software,the crushing resistance and fluid flow state of the original flower tube and the gathering flower tube are sim-ulated and analyzed.The study shows:The use of a 1 meter length gathering flower tube increases the gas flow rate by 42.5％compared to the original flower tube,and increases the flow area by 152％,increasing the gas flow rate of a single hole while increasing the negative pressure contact area between the flower tube and the borehole;When different confin-ing pressures are applied externally to the flower tube,the deformation of the gathering flower tube is always less than that of the original flower tube,and most of the pressure is borne by the external flower tube,providing good protection for the internal flower tube;The fluid flow in the original flower tube is relatively chaotic,whereas the fluid flow in the gathering flower tube is stable,effectively preventing the generation of vortices in the extraction pipe,reducing energy loss in fluid flow within the pipe,and enhancing gas extraction flow rate within the perforated pipe.Field industrial comparative test results show:at the beginning of extraction,the gas concentration and flow rate of gas extraction boreholes using two types of flower tubes are similar;after 60 days of extraction,the average gas concentration of the experimental group us-ing the gathering flower tube is 50.7％higher than that of the comparison group using the original flower tube,and the av-erage gas flow rate is increased by 57.1％.As the extraction time extends,the decline in gas concentration and flow rate in the test group boreholes is slower,indicating that the extraction effect of boreholes using the gathering flower tube is bet-ter than that of boreholes using the original flower tube.Gathering flower tube increases gas extraction flow rate and con-centration,shortening the gas control cycle of coal seams.