If you drill into formations which have a lot of bentonite,
you might need to use Lignosulfonate mud (fresh water lignite mud).
The Bentonite in formations are easily dispersed by water and the
dispersed bentonite will cause higher viscosity and rheology
. The lignite added into the water mud will control this problem and it
is not expensive. Many people love using this mud because it can be
weighted up to almost 19 ppg but it still has very low value of low gravity solid.
You still have some disadvantages from this system. The
Lignosulfonate mud does not have shale stability like others as low
solids non-dispersed fluid, PHPA mud, KCL base mud, and salt water
system. Moreover, some additives as carbonate can cause contamination in
the mud and degrade mud property. You should be careful while using the
Lignosulfonate mud with some chemical additives.
source : http://www.drilling-mud.org/lignosulfonate-mud-fresh-water-lignite-mud/
