Unplanned sidetracks while enlarging the hole with a drillbit

Folks,

We have a customer who wishes to enlarge the hole from 12 1/4" to 22" with a rotary BHA.The BHA proposed is packed hole assy with tricone bit without a hole opener in the assembly  The trajectories are vertical at this point. Total interval to be drilled is about 700 m.

Top 400m of the lithology is clay/sandstone and bottom part is dolomitic limestone

We are conscious that this represent a risk of sidetracking the well and would would like to minimize the risk by leading a bullnose into the hole with a stabilizer and enlarge with a hole opener. Our customer has opened the hole using the bit in the past and doesn't see the point in a hole opener deployment.

Can anyone share best practices out there with enlarging such hole size in rotary BHA without hole opener and still manage to avoid risk of sidetracking?

Cheers,

Ken

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