My understanding of drilling muds is limited, but I understand that mud serves several purposes...
It acts as a lubricant and coolant for the drill It acts as a conduit to remove the drilling material It also acts as a weight to maintain a balanced well.
I'm sure there are other uses...
Now we know they aren't quite there yet, so the only reason I can see to switch to a lighter mud is to increase the drill rate, as heavier mud does not transport the drilled material as effectively as lighter mud, since heavier mud is more viscous.
My thoughts...probably wrong...but thats the inital ideas running through my head 8P.
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