Drilling 6" hole ahead of 8-1/2" hole already drilled

Onshore rig Ops

Drilled 8-½" hole to 3500 m MD (inclination 35 deg) at section TD. RIH 7" Liner, stuck at 2600m MD. 

HQ input says to cement the liner in place and drill ahead 6" hole to well TD i.e. having an existing 8-½" hole from 2600m MD to 3500mMD and then drilling 6" hole to well TD at 4000m MD (inclination/azimuth hold).

There are obviously problems to this, hole cleaning being the obvious one. 

We'll be drilling with standard RSS+MWD. 

What possible problems could I face and are any mitigations recommended?

PS: the 8-½" open hole formations are very stable so longer exposure is not an issue in terms of hole stability - also no reservoir zone in the 8-½" hole section. 

12 Answer(s)

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