Slug Volume & Pit Gain
The slug volume needed for a desired length of dry pipe before tripping, and the pit gain that slug will cause once it's pumped.
The Formulas Used
Where This Fits
The slug volume figure feeds directly into the pit gain calculation — pump the slug volume from the first box, then use that same figure in the second box to know exactly how much pit gain to expect from the U-tubing effect alone. That expected number is what a crew checks the actual pit-level reading against right after pumping a slug, on any trip, which is also the same routine sanity-check habit that matters on the stuck pipe and fishing operations page's broader trip-monitoring discussion — an unexplained gain beyond this predicted figure is the first real sign something else is happening in the well at the same time.
Frequently Asked Questions
Why pump a slug before pulling out of hole?
A slug is a small volume of heavier mud pumped into the top of the drill string before tripping, so that once the string is broken and drained at surface, the pipe comes out with a known dry section instead of dumping mud onto the rig floor at every connection. It's a housekeeping and safety measure, not a well control barrier.
Why does pumping a slug cause a pit gain?
The slug is heavier than the mud already in the pits, so pumping it in and displacing an equal volume of lighter mud back to the pits — the U-tubing effect — shows up as a real, expected pit gain. Confirming this expected gain matches what the calculator predicts is exactly how a crew rules out a real kick showing up at the same moment a slug is pumped.