Through soaking experiment, swelling time of carbonaceous slate respectively is 5 #> 4 #> 2 #> 1 #> 3 #:
1# has a good viscidity, but low inhibition and less strength after swelling;
3# has a good encapsulating ability, but also less inhibition and short swelling time;
4#, 5# is ok;
5# mud is optimized from the 4#, and has better rheology.