N/A Equipment LL with Wellesley

Kallåsen (35/12-6 S) – Surface section

What happened:

Disadvantage of using MRR system: Drilling top hole with reactive clay formations using mud will create a gauge hole with correct mud, but does not prevent clay formations to swell over time. When tripping out, the hole diameter has decreased and bit & stabilizers may ball up which causes difficulties and may cause the need for backreaming. This in turn usually leads to packing off which is hard to see without proper active volume control. This again leads to losses during cmt job, and possibly poor LOT.

What was planned:

Use MRR system

What was learned:

Unless there is high probability of overpressured gas or water, it is quicker, less costly and with lower risk to drill a pilot/main hole with SW and sweeps. The SW will wash out the hole and allow for clay swelling without reducing hole diameter below bit/stab size. It is usually easy to trip out. Mobilizing (heavy lift) and rigging up a MRR system requires good weather.

What actions are required:

Keep in mind disadvantages when considering use of MRR system. Do not use if not strictly necessary.