Suction from lifting drilling tools

[LRJ]

I understand that lifting tools from an open drillhole on the seafloor can be critical for hole stability due to the suction that results from lifting these tools. My question is: what methods exist for predicting the magnitude of this suction?

 

[BUGGAR]

Boyle's Law?

 

[LRJ]

I'm not sure that's applicable in this case as it is not a constrained volume of fluid/gas - it is open to the sea. I'd also expect the velocity of lifting to have an impact on the pressure at the drillhole wall too.

 

[chicopee]

If you keep the rotation going as you lift would you expect suction to be a problem?

 

[berkshire]

Do you not have down head lubrication on the drill ? Increasing the slurry rate should stop the suction event. If you do not want slurry in the hole , you can always pump water.
B.E.

You are judged not by what you know, but by what you can do.

 

[LRJ]

Why would rotation reduce the suction effect? Would that not make shear stress greater on the wall?

Pumping (overpressure) could also lead to hole collapse, but it does seem like a good counter to the suction (underpressure).

I was looking for ways to calculate the amount of suction on the wall. I've not seen any methods, so maybe it has not been studied and/or is not a practical concern due to mitigations like suggested above?

 

[chicopee]

I don't have any mathematics explaining the reduction in suction when you rotate the drilling process, however, on a much smaller scale when a drill bit gets stuck in a piece of metal or wood, rotating the drill bit seems to loosen it as it is being retracted. In a similar fashion rotation may break the bond between the saturated soil and the drill and then extract while rotation is going on.

 

[LRJ]

In this instance the drilling equipment isn't usually in contact with the ground - it is just being lifted through a fluid, thus causing suction. I'm unsure how to calculate the magnitude of that suction for a wellbore stability assessment.

 

[BlackJackJacques]

The amount of suction would largely depend on the clearance between the drill shaft and the bore hole, number and size of equalization ports, if included. Speed at which you remove the drill shaft will play a role, especially if the clearances are tight and too few or no equalization channels. Think of a hypodermic syringe for example.
For purposes of determining compensation through say a water injection means to minimize over or under pressure, I would assume a tight clearance as in the hypodermic syringe example and figure head differential and flow rate based on the volume of the bore, etc. In theory, you can pull the piston out as fast as your compensation controls and pumps are stable.