A lot of well teams are now moving rigs at deep draft. The slower
transit rate is compensated for by the time saved ballasting & de-
ballasting. Each rig move is risk assessed. One team even decided to
start ballasting down on approach to location after they had passed
over the last of two pipelines.
Does anyone have any comments or insights?
This has been done many times in Asutralia and Africa, (3rd & 5th
gen rigs) and based on cost benefit of move time vs ballast time.
Some practice is required by crews to get the timing right if you
try to "come in to land" as you approach location. You can even try
to start running a spud BHA at the same time once the vessel speed
is low enough so that you are ready to spud as soon as you have
completed beacon deployment (DP vessels) and positioning.
The main issue for going from transit to drilling draught is going
through the transition zone, when all drilling related activity must
stop for a short period. For an anchored vessel, power distribution
(anchor winches vs draw works) also needs to be well managed.
Depending on the seperation between wells, if you batch drill
surface hole then you can transit with riser and BOP suspended so
that you save on BOP/riser running times, which in deep water are
significant. This has been done successfully on exploration wells in
West Africa, and on a field development using subsea templates.
Issues which require resolution are VIV analysis/monitoring and
insurance coverage for Drilling Contractors. Some Contractors find
it difficult to believe it can be done safely or may be unwilling to
try, so tactful offshore management is required.