You may have heard about Surge Pressure, Swab Pressure and Trip margin in the drilling business. Today, I would like to share my knowledge about these terminologies.
What is surge pressure?
Surge Pressure: When pipe moves downward with mud circulation through drill string, additional bottom hole pressure called “Surge Pressure” is created. If surge pressure is too much, many problems will occur as formation brake down, partial mud loss and lost circulation.
What is swab pressure?
Swab Pressure: If a drill string , casing string or logging tool is being pulled out of hole too fast, due to bigger diameter almost same hole size, BHA/ bit, casing or logging tool will possibly swab mud out of hole, like pulling small a piston of syringe. For this reason, hydrostatic pressure of bottom hole will be reduced. Pressure reduction created by this situation is called “Swab Pressure”. If swab pressure is too much, kick (wellbore influx) may be into the hole and well control must be conducted in order to secure well.
What is Trip Margin?
Trip Margin: It is an increase in the hydrostatic pressure of mud that compensates for the reduction of bottom pressure due to stop pumping and/or swabbing effect while pulling pipe out of hole. Trip Margin is calculated by following equation:
How do we calculate trim margin?
The formula used to calculate trip margin is listed below;
Trip Margin (PPG) = (Margin needed (Psi) – Present Margin (Psi))/ (0.052xTVD (ft))