1. n. [Drilling]
The act of putting drillpipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. This is necessary when a kick is taken, since well kill operations should always be conducted with the drillstring on bottom, and not somewhere up the wellbore. If only the annular BOP has been closed, the drillpipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then the ram closed again. This procedure is repeated whenever a tool joint must pass by a ram BOP. Rig crews are usually required to practice ram-to-ram and ram-to-annular stripping operations as part of their well control certifications. In stripping operations, the combination of the pressure in the well and the weight of the drillstring is such that the pipe falls in the hole under its own weight, whereas in snubbing operations the pipe must be pushed into the hole.
2. n. [Well Workover and Intervention]
The running or retrieving of a tubing string in a well under pressure, using a stripper or similar sealing device to contain well pressure and fluids. Coiled tubing, snubbing and some specialized workover rig operations can be conducted on live wells using special sealing equipment to safely and reliably contain wellbore pressure and fluids. Well-intervention systems designed to operate on live wells incorporate a secondary or contingency means of isolating wellbore pressure.