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Catfish · 05-01-10, 01:39 PM

Hello Tribesman,

you wrote:
" Catfish can you please explain the basics over a blowout on a new drill "

What exactly do you mean ? When drilling has begun, and the "spud-in" has been initiated, there is usually a lot of cementing done, and along with cementing the upper liner and the Blowout-preventer (BOP) set. On offshore rigs this device also sits directly on the upper end of the borehole, so here certainly underwater.
The liners are going up through clear water, up to the drilling rig, which is held in place by dynamic positioning (via GPS) - meaning engines hold the rig in place, instead of anchors.

While drilling, regardless rotary, turbine (downhole motor, Moineau system) or coil tube drilling, there is drilling fluid ("mud") used, pumped down within the drilling tubes, leaving the tube via jets in the bit, and rising within the angular space between drill tube, and borehole.
This drilling fluid serves numerous purposes and has developed into a highly complicated substance:
- It cools the "bit", or drilling head (may also drive the turbine motors when in slide mode or coil tubing)
- transports the chipped material from the bit to the surface
- Keeps the borehole open, before it is lined and cemented
- prevents gaseous stuff to enter the borehole in low-pressure conditions
- keeps the stony chips in suspension when rotation or pumping is stopped (via clay minerals, wet when moving, almost solid without being moved, "thixotrope")
- lubricates the turning or sliding tube
and numerous other applications.

One of the most important tasks is to control pressure in the borehole, which will rise with the depth, and - if the bit penetrates a dense layer entering a high-pressure area - can help to control a "kick" (the sudden pressing out of tubing and fluid out of the borehole) through ballasting the fluid with heavy substances, like e.g. baryte, to make it specifically heavier.
It can also help losing the drilling fluid when entering salt domes, in which case the fluid is heavily salted to prevent washing out caverns.

The drilling fluid has to be constantly observed, cleaned and chemically changed, to adjust to the downhole conditions.

When e.g. an oil or gas depot has been found, there will be a sudden pressure rise, and - if you do not pay attention - the whole mile(s)-long drill tubing will be pressed out of the borehole, which becomes very hot during this "kick", and will easily ignite any explosive gases that may be around, in the reservoir, or aboard the rig.

Should the fluid be too light to control the pressure in the borehole, the blowout-preventer can be used to control the well, but this will seal the well-entry permanently, by sheer brute force.

The problem with offshore rigs is that you can only remote-control the BOP, via electric, hydraulic or "sonic" telemetry (pulser), and if the fluid is leaking out the pulsing telemetry will not work well. Using a pulser to control directional or any other drilling under normal circumstances is difficult enough.

So the technical staff developed further well control and seal-off systems while drilling, but this is only a regulation in Norway, and Brazil (and a few others, but not in the US).

Additionally if you let the well develop its pressure increase without instantly controlling it, the former fluid substance will turn to gaseous phase, and thus develop a higher pressure and speed going up in the borehole, drastically amplifying the effect.

I will be crucified when my coworkers read this, but all else will take several pages ahem

Greetings,
Catfish

05-01-10, 01:39 PM	#49
Catfish Dipped Squirrel Operative Join Date: Sep 2001 Location: ..where the ocean meets the sky Posts: 17,817 Downloads: 38 Uploads: 0	Hello Tribesman, you wrote: " Catfish can you please explain the basics over a blowout on a new drill " What exactly do you mean ? When drilling has begun, and the "spud-in" has been initiated, there is usually a lot of cementing done, and along with cementing the upper liner and the Blowout-preventer (BOP) set. On offshore rigs this device also sits directly on the upper end of the borehole, so here certainly underwater. The liners are going up through clear water, up to the drilling rig, which is held in place by dynamic positioning (via GPS) - meaning engines hold the rig in place, instead of anchors. While drilling, regardless rotary, turbine (downhole motor, Moineau system) or coil tube drilling, there is drilling fluid ("mud") used, pumped down within the drilling tubes, leaving the tube via jets in the bit, and rising within the angular space between drill tube, and borehole. This drilling fluid serves numerous purposes and has developed into a highly complicated substance: - It cools the "bit", or drilling head (may also drive the turbine motors when in slide mode or coil tubing) - transports the chipped material from the bit to the surface - Keeps the borehole open, before it is lined and cemented - prevents gaseous stuff to enter the borehole in low-pressure conditions - keeps the stony chips in suspension when rotation or pumping is stopped (via clay minerals, wet when moving, almost solid without being moved, "thixotrope") - lubricates the turning or sliding tube and numerous other applications. One of the most important tasks is to control pressure in the borehole, which will rise with the depth, and - if the bit penetrates a dense layer entering a high-pressure area - can help to control a "kick" (the sudden pressing out of tubing and fluid out of the borehole) through ballasting the fluid with heavy substances, like e.g. baryte, to make it specifically heavier. It can also help losing the drilling fluid when entering salt domes, in which case the fluid is heavily salted to prevent washing out caverns. The drilling fluid has to be constantly observed, cleaned and chemically changed, to adjust to the downhole conditions. When e.g. an oil or gas depot has been found, there will be a sudden pressure rise, and - if you do not pay attention - the whole mile(s)-long drill tubing will be pressed out of the borehole, which becomes very hot during this "kick", and will easily ignite any explosive gases that may be around, in the reservoir, or aboard the rig. Should the fluid be too light to control the pressure in the borehole, the blowout-preventer can be used to control the well, but this will seal the well-entry permanently, by sheer brute force. The problem with offshore rigs is that you can only remote-control the BOP, via electric, hydraulic or "sonic" telemetry (pulser), and if the fluid is leaking out the pulsing telemetry will not work well. Using a pulser to control directional or any other drilling under normal circumstances is difficult enough. So the technical staff developed further well control and seal-off systems while drilling, but this is only a regulation in Norway, and Brazil (and a few others, but not in the US). Additionally if you let the well develop its pressure increase without instantly controlling it, the former fluid substance will turn to gaseous phase, and thus develop a higher pressure and speed going up in the borehole, drastically amplifying the effect. I will be crucified when my coworkers read this, but all else will take several pages ahem Greetings, Catfish Last edited by Catfish; 05-01-10 at 03:00 PM.