Experimental research on decreasing coalbed methane formation damage by using low density cement slurry

By comparing the loss of water, the filtrate performance and thickening time of low density cement slurry used in Bohai Drilling (hereafter called as Bohai drilling slurry) and conventional cement slurry, through analyzing their composition, conductivity, permeability response rate, the paper calculates the pollution radius, evaluates the ability of Bohai drilling slurry to reduce the damage of CBM reservoir. The results showed that water loss of the Bohai drilling slurry was 50% less than that of the conventional cement slurry.And filtrate viscosity is high, salinity is low and conductivity is low. So the permeability of coal contaminated by Bohai drilling slurry was reduced to 28.97%, the recovery rate of permeability was 89.81%, while the permeability of coal contaminated by conventional slurry was reduced to 65.87%, permeability recovery rate was 61.18%. With the integrative consideration, Bohai drilling slurry is not only low-density, which forms small pressure and ensures stable coal, but also reduce pollution radius and the coal reservoir damage.