When a well is shut in due to well control operation, the casing pressure will increase due to gas migration and gas expansion. In water based mud, you are able to estimate the maximum surface pressure with this following formula.
Where;
Max surface pressure in psi.
P is expected formation pressure in psi.
V is pit volume gain in bbl.
KWM is kill weight mud in ppg.
An is an annular capacity in bbl/ft.
