I'm a bit in the dark about how the mud system works. For...

I'm a bit in the dark about how the mud system works.
For example everything was going very well until they encountered very high pressures in the LA. So they upped the mud weight.
So my question is this.... after they increased the mud weight to cope with the high pressures in the LA (probably 3,400 metres and deeper) does this mean the heavy mud is now circulating and effecting the shallower parts of the well that was drilled with much lower mud weight.

I don't know enough about how the mud system works to even make a sensible guess about the answer.

Saltbus