Snubbing (pushing) or stripping (pulling) pipe in and out of a live well bore under pressure is a really cool thing. Snubbing becomes necessary when the well cannot be killed, or it is unadvisable to kill it - for instance if the pressure involved is so great a shut in might exceed the frac gradient of rock in the subsurface, or casing/cement integrity might be at risk. Underground blowouts, where one formation is producing, uncontrolled, into another formation, is an operators worse nightmare.
Snubbing units can be "stand alone" units or they can be something called, "rig assist" units, the later are much smaller and can be rigged up under a workover derrick. They are all hydraulically operated. We can push/pull production tubing in and out of a live well, fish stuff, set packers, release packers, drill out frac plugs; whatever we need to do with a workover rig we can do with a snubbing unit. It just takes longer. And costs more money. The snubbing unit jacks the pipe, up or down, with thousands of short strokes, so to speak, while opening and closing various "BOP" rams that allow gas, etc. to bleed off (get flared to a fare pit) between ram bodies, spools, spacer joints, etc. etc.
Snubbing has been around for a long time; I get a kick out of non-oily types, mesmerized by the shale phenomena, that call this "new technology." Phfttt.
Snubbing stack configuration
below the basket, or work floor; allows the well to be opened and closed to facilitate pipe movement, gas to be released and vented, or flared, the well still under control.
Here is a little clip of what I mean by "jacking" pipe in or out of the hole. This is a little rig assist snubbing unit under a workover rig. The are stripping pipe out of the hole. There are stationary slips and traveling slips with grapple segments that hold the pipe. Below them BOP pipe rams are being opened and closed and gas/fluids under pressure are being bleed off, separated and or burned off. Each joint of tubing as to be broken out with tongs and laid down on the ground via a gin pole and winch system, also part of the snubbing unit's components. A round trip on a 12,000 foot vertical well takes forever, obviously.
Here is a photo of a stand alone snubbing unit working somewhere in Venezuela. Generally speaking the higher the stack the more pressure the well is under. They're flaring gas off to the left. This is a big operation.
Some snubbing stacks can be way up in the air, man. I mean WAY up there. Here is a photo I took of my buddy at Boots and Coots, David Thompson, on a big, high pressure well in Lysite, Wyoming in 1992. We are being picked up by a crane and the snubbing basket is just to the right of us We are almost to the top. Below you can see the size of Halliburton trucks at the flare pit. This stack was a big sumbitch.
Most good well control hands come from snubbing backgrounds. Why? Because to be a snubbing hand you have to have giant nuts. You are essentially working in a tiny, very crowded basket, 100 plus feet in the air, with anywhere from 3,000 to 13,000 pounds (or more!) of pressure under your feet. Its like sitting on a damn rocket that all of a sudden, for a host of reasons, could get lauched at any time.
When things go wrong in a snubbing basket there is no where to run. You can bail out for the crane basket, like David and I are in, or hook on to safey lines and try your best to slide down to the ground before getting blown up or burned to death. Over the years lots of snubbing hands have perished working on high pressure wells; you've got to be a tough son of a bitch, with no fear. That transfers well into the well control, oil well firefighting business. Pressure either bothers you... or it doesn't.
I love this little clip, above, as it orchestrates exactly what I'm talking about. This is not a snubbing unit and the size of the rig floor on this workover rig is bigger than a typical snubbing basket. This well has kicked and its now in their faces, big time. Nobody runs. There's no place to go and that does not fix the problem. There is some hollering going on in this video, just to be heard; everybody still on the floor knows what needs to be done.
They're TIW safety valve (closing valve) is screwed into a kill joint laying on the rack, open, of course. They pick that entire joint up with the rig and block and try to stab the kill joint into the blowing tubing. Clearly that is easier said, than done. Whatever your trying to stick on a blowing well, the well is trying like hell to blow it back off. You have to stay calm and carry on... get the well back under control. Shit is in your eyes and you can't see anything. It stings, hurts and the longer it takes the harder the well blows. As long as its still wet, and watery, you are OK. When it unloads and gets gassy, or oily, your butt starts to pucker a little. Been there, done that many times.
At about the 3:30 mark in this video they get the kill joint stabbed and can get the tongs on it to make it up tight. They pull that joint out the slips, lower it down hole with the rig block and shut the TIW valve. The well is under control again. Same thing would have happened in snubbing situation; they would have had to have jacked the kill joint in the hole to close the TIW valve.
The hands in the video, above, will take a break, get cleaned up and pat each other on the back. They'll trust each other tomorrow more than they did yesterday, believe me. Nobody back in the office will give a shit one way or another if this happened or not.
Here's a photograph of a snubbing crew in the Gulf of Mexico on a big rig assist unit under a drilling rig. This well has just come to see them, big time, with nasty mud. They held their ground, got stinking dirty, but regained control, saved the well, and likely the entire platform. They're proud. They should be.
Snubbing hands have big nuts.
And, by the way, after their hitch snubbing hands can out drink and raise more hell than any other service personnel in the entire oil and natural gas industry. Times six.