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Hole opening in shallow deviated well
30 August 2019
We are planning a shallow horizontal offshore well.

Well configuration is 30" @ 100 mMDRT (50m below seabed).

 A 22" open hole interval is planned from 30" shoe to ~360 mMDRT.

The tentative well trajectory is kick-off at 150 m, build rate of 3-4 deg/30m to achieve 21-28 deg inclination at section TD of 360 mMDRT (350-355 mTVDRT).

Given the very soft formations and associated difficulty in building inclination, it is planned to drill a 17.5" directional hole and then open up to 22" in a separate dedicated hole opening run.

Is there any experience of hole opening similar shallow deviated wells? And any lessons that would help in designing the well? What sort of penetration rates can one expect in this scenario?
2 answer(s)
Drilling Engineer
Norwell Engineering
Total Posts: 6
Join Date: 27/09/09
Hi Rajiv,

It may be worth a discussion with the DD contractor to determine how far you can reduce the flow rate and retain usable power at the bit. There could be potential to operate the PDM at a lower flow rate than the spec sheet states dependent upon how much grunt you need at the bit.

As a word of caution - if the inclination is hard won, care should be taken that it is not lost while circulating and cleaning up the hole. Keep pipe moving during circulation, rack back stands to minimise undercutting the hole etc. Assess the pros and cons of orienting high side and circulating rather than rotating the string during clean up. 

All the best!
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 432
Join Date: 10/01/05
CAN technology has been used to establish a conductor base for the well. This permitted a much shallower kick of and a more preferred trajectory to results desired to get to a much shallower reservoir target. 

If water depths are quite shallow I would suggest you assess the use a mud recovery system.

The above technologies afford more drillable hole and require less build rates. Drilling with weighted (inhibitive mud if needed)  will afford better stability and getting to inclinations desired 

We did some shallow directional development work in central North Sea circa . After running and cementing  160-200ft 30in x swedged down conductors We opted to batch drill with the BOP and opted for a slender design vs using a mud recovery system. We opted for a 17 1/2 bi-cone bit (TcTi+cR) S.N PC451,  on a motor wit a bent sub as we assessed this would permit easier sliding to get angle required and more rotation. We hopped the SSBOP from well to well using a tool the wellhead manufacture built for us. This saved us a lot of time.

Same bit accumulated 14,609ft of hole to various shoe angle setting depths with on bottom ROP's bit runs varied from 218-440ft/hr per well. ( Lithology was soft drilling with lots of long sand intervals (and why we needed to drill this with a mud system) that made this a lot more treacherous than drilling clay!)

At that time we did not use a mud recovery system because we assessed it as too expensive. Today this may be far more accessible better (there is a new generation  of these) and affordable. 

Hole opening from 17 1/2 to 26" again should not be an issue as long as best practices are applied. This was common old school 80's 90's practices in many offshore development projects. We had to drill wellbores in two section because drilling a 26" with the mud pumps we had was a tedious and very risk chore. It was therefore delivered in two separate phases.

Wishing you success.

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