Study on inhibited plugging additives of drilling fluid for coal-bearing strata

The fractures develop, are complex and variable in coal-bearing strata, accidents occur frequently during drilling. As for this phenomenon, this paper worked from the analysis of microstructure of strata, and it was found that in the coal measures exist a large number of micro cracks containing plenty of water-sensitive inflating fillings, easily leading to the instability of coal measures. The use of Xanthan XC to reduce filtration loss and the use of ultra-fine inert material to seal the pores of coal-bearing strata and reduce permeability can reach the effect of blocking water intrusion into coal strata. Therefore, the additives of inhibitory drilling fluid system were analyzed and sifted by combining theories and experiments. The rheological and filtration properties of base slurry were tested by laboratory experiments in which different dosages of high polymer Xanthan XC, ultrafine inert material Nano silica and superfine calcium carbonate were added. With the analysis of the experimental data and simulation results, the rules were found about how the performance parameters of slurry change with different dosages (mass fraction) of XC, nano silica and superfine calcium carbonate added. The inhibition effect of XC polymer drilling fluid system was supported by expansion test and the mechanism of action of the three kinds of additives is explained from the perspective of microstructure. The research results provide a theoretical basis for the drilling of coal-bearing strata, and have certain reference value in the drilling of other strata which are similar to coal-bearing strata.