Optimal Pilot hole size as water depth increases?

06 May 2011 In deep water shallow sections where flow hazards exists (often stated as 500-2000ft below the mud line).

With > water depth where we know there is an associated reduction in the drilling window as fracture gradients decrease.

Finally as the IADC deepwater guidelines state that shallow zones are likely to flow with 100-300psi over pressure. 8.6-9.3ppg por pressure.

Ascertaining optimal kill mud weight?
The rate we pump to kill?
Pilot hole size of the wellbore to kill the well?
Without fracturing etc?

Surely is not as straight forward as stating we must drill a 8-1/2" or 9-7/8" pilot hole because regulation or pure in-guage wellbore dynamics modelling states this?

Where when one looks at turbulence generated in such small holes, surge, cuttings effects etc in formation that are likely 40-80% porous, very soft, incompetent etc.

Is there not therefore a case by case Hazard/risk analysis need to determine the optimal hole size? That may equate for all the right reasons to be bigger than 9-7/8" etc.

Further supported by fact we can pump a lot faster with the bigger pumps and kill e.g. a larger pilot hole that is less likely or prone to destabilise, washout and/or fracture the well.

Comments, suggestions from deepwater regions appreciated.

9 Answer(s)

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