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?
Is it right to assume, because you are referring to a bullnose, that this is a two-stage process with the 12¼" section already drilled?
I would certainly be very uncomfortable without either a bullnose or the original 12¼" pilot-hole bit in the BHA (below the hole-owner)and would recommend a 4-6 point hole opener.
I hope this helps