Application Research Of Gas Pre-drainage Technology By Hydraulic Fracturing Permeability Improvement In Mapu Coal Mine

In view of the low permeability of coal seam in China,the small amount of gas extraction and the low extraction rate,the high-pressure hydraulic fracturing and anti-reflection technology of low-permeability coal seam is studied,and field test application is carried out in Mabao Coal Mine.This paper mainly studies the hydraulic fracturing pre-extraction gas technology.Through the combination of theoretical analysis,numerical simulation and downhole test method,the hydraulic fracturing anti-reflection technology is systematically studied,and the field test and application are carried out.The research contents include:hydraulic fracturing mechanism of low permeability coal seam;analysis of hydraulic fracturing mechanism and influencing factors;numerical simulation of hydraulic fracturing and permeability analysis,and analysis of the influence of loading step,ie water pressure,on crack initiation and propagation And the influence of different drilling arrangements on the fracturing effect;based on the theoretical analysis and research of the 15201 return air trough of Mabao Coal Mine,combined with the research results of on-site industrial tests,comprehensive evaluation of hydraulic fracturing and pressure relief effect.The research results of this thesis:The mechanical mechanism of borehole coal seam anti-reflection under non-uniform stress field is studied.Theoretical analysis was carried out on the factors affecting the cracking pressure and crack propagation of hydraulic fracturing through the layer.The hydraulic fracturing simulation was carried out by RFPA^2D-Flow software.The crack initiation,extension and expansion laws were studied by changing the drilling arrangement and fracturing method.The influence of the drilling on the surrounding ground stress was considered to make the surrounding area of the hole.Stress redistribution.After the hole is finished,the stress of the rock near the borehole will change,and the stress distribution will reach a new balance due to time.The stress field at this time is different from the original stress field,and the crack initiation and crack extension are also different from the original stress field.It is concluded that due to the induced stress,the first developed crack may affect the expansion direction of the later developed crack,making it easier for the crack to communicate with other cracks and form a network crack.The mechanism of hydraulic fracturing and anti-reflection is revealed.The research results were carried out in the Mapu Coal Mine,which improved the gas drainage efficiency by 3.55 times and the gas pressure relief effect was obvious.The thesis has 36 pictures,9 tables,and 61 references.