36″ Underreamer

Hi,

We are drilling a well with a jack up through a platform in the UK SNS. Our normal top hole BHA is a 26"× 36" HO with a motor. On the platform, the guides are 35.4" ID, and so we cannot use the 36" HO (we run 30" conductor with 32" connectors). The 1st well we drilled with a 26" bit and a 36" Smith Underreamer (22000 DTU). We could not put a motor on the top of the  Underreamer because the Underreamer was not good for the RPM. The result was slow drilling (60 hours instead of usual 18 hrs for the section). The next well we ran a 26"×35" HO with a motor. We had lots of problem running the conductor and now for the 3rd well, want to go back to a 36" hole.

Does anyone have any experience of using a 36" Underreamer with a motor on the top? Anyone got any ideas of the bext way to do this? The formation is mainly hard chalk (vibration, bit bounce etc...)
Thanks in advance

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