Experimental study of foamed cement slurry for soft coal seam reinforcement

Abstract:

In view of the problems of low success rate and low mechanical strength of long drilling holes along the soft coal bedding， the technical idea of injecting mechanical foamed cement slurry into the soft coal seam by the way of high-pressure rotary spraying while drilling to inforce the fomation is proposed. In the laboratory test， the proportion of soft coal rock and foamed cement slurry was changed to simulate the soft coal rock and foamed cement consolidation body which has different consolidation effects after grouting. In addition， taking compressive strength and gas permeability as the main evaluation indicators， the influence of soft coal content on the performance of the consolidated body was studied. The results show that： （1） Compared with the consolidated body of pure foamed cement slurry， when the content of soft coal rock （hereinafter referred to as “coal content”） was 5%， the gas permeability of the consolidated body decreases slightly， and the gas permeability decreased with the increase of curing time； （2） When the coal content was greater than or equal to 10%， the gas permeability of the consolidated body increased with the increase of coal content； （3） The early compressive strength （cured for 1d） of the consolidated body increases first and then decreases with the increase of coal content. After 7 d of curing time， the strength of the consolidated body decreased with the increase of coal content； （4） After the coal content was between 20%~25% and the consolidation body was cured for 7 d， the compressive strength was 8.65~9.94 MPa， and the gas permeability was 9.08~36.52 mD. The research results can provide useful reference for the wall protection while drilling and gas extraction in soft coal seam.

Key words:foamed cement;soft coal seam;consolidated body;gas permeability;compressive strength