User:Sagar2652/sandbox

Trip margin is addition of drilling or completion fluid density that provides an increment of overbalance pressure in order to compensate for effects of swabbing.

During pulling out, upward motion of the drill string in the borehole(which is assumed to be full of mud) creates a swab pressure. This decreases Bottom Hole Pressure when pipe is in motion. One way of minimising this is to use safe tripping speeds and having close monitoring of pipe volume pulled out and mud volume pumped in to keep the hole full. Another practice to tackle the problem is to keep mud weight gradient greater than the formation pressure gradient. The resulting overbalance permits safe tripping and connection operations.

Formula
For normal drilling operation trip margin is kept 0.2 to 0.3 ppg. However, the swab pressure being a function of yield point(yp) of mud, trip margin can be calculated as follows:

Trip margin (ppg) = 8.33*yp ÷ 98(dh-dp)

where yp = Yield point of mud (lbs/100sq.ft), dh = Hole diameter (inches), dp = Pipe outside diameter (inches)