Ken
Gather the evidence?
e.g. does the customer have a before and after survey of the pilot hole and final opened wellbore drilled? i.e. To demonstrate or not, that they have drilled and opened the same hole on previous offset wells?
Where Drilling log trends should evidently inform you if there is a suspected sidetrack of not. Or as stated by the customer this regional way does in fact work.
One would suspect you have an evident potentially faster drilling sequence (the first 400m) and then a much slower drilling sequence the 300m further (dolomitic limestone?).
I am surmising the reasons section is delivered in two passes is because rig does not have the capability to pump at a high enough flow rate to drill and clean a 22in hole optimally?
Notably silts/sands in first 400m?
To be optimal? Drilling a 14 3/4" hole first would seem more prudent?
This leaves far less well to hole-open (can be a slower process than the drilling) particularly in the last 300m.
vs a 12 1/4" pilot hole then a 22in main well adds more risk surely to the 2nd run?
Where if customer does not wish to run a 12 1/4in bit and/or bullnose (stabilised short lead) and a packed 22in hole opener assembly behind. (Note: This was always our standard in SE Asia in the 80's (when I was the driller doing and would have no issues with this approach.)
The other big issue for me is the tools in your region?. w.r.t hole-opening 300m of dolomitic limestone. Where if you do not have suitable hole opener they will likely fall apart. (se file i compiled in 2000 as attached).
With the larger pilot hole. Then the probability of a 22in bit NOT following the main 14 3/4" pilot well is physically greatly reduced (where it is far more likely to follow the least path of resistance) in the softer formations
as long as pipe is kept moving.
In the
dolomitic limestone? as long as 22" BHA is suitably stiff and rigid, one would have to be stationary for quite a long time to side-track the well.
The drilling log from the pilot hole should be indicative of exact depth where stingers etc are expected ( and where areas of greatest side-track hazard/risk are presented) So these should be able to be suitably managed.
The 'best practice' essentials on these sections is always to assure the pipe is kept moving. In both shallower softer and deeper slower drilling sections.
Success.
