Page 392 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 368

[ ] Practical Wellsite Operations
3.3.5

If a backup charge is to be used, it should now be set on depth and
fired while holding torque with the tongs (i.e., without the rotary table
locked). Watch out for the string lashing back as the torque comes off
and watch the weight indicator for indications that the string is free.
Often the drillstring will loosen off in several places other than the
actual depth that backed off. Be very steady pulling out of the hole, set
the slips gently and do not rotate the string. Always check that all the
connections are fully torqued up when running back in. If any con-
nections are visibly backed out when tripping out, set the slips gently
underneath and make up the connection right away so that a very loose
connection is not racked back to be picked up later with string weight
underneath it.
If attempting a purely mechanical backup, work more torque down
the string a bit at a time, lowering the string this time to the lower of
the two lines until something backs off downhole. Do not exceed the
combined torque/pull limit of the pipe, or stop earlier if damage to the
pipe body by the tong is causing concern.
If backed off in the wrong place. It is sometimes possible to screw
back into the top of the fish and attempt a backoff at a lower depth.
Work in RH torque in the same manner as described above, to ensure
all connections are screwed in before making your next attempt.
The chances of success are lower than for the first attempt. Hold
more tension when working the pipe to increase the chance of getting
a backoff lower than before.

3.3.5. Fishing Operations

What follows is general advice on fishing jobs. It is not meant as
an exhaustive guide to fishing! Where the fishing job may be compli-
cated and/or take a long time it may be worth getting out a specialist
fishing hand and tools.
When anticipating a fishing job, record as much information about
the fish as you can. In particular you need to know:

1. Condition of the top of the fish: cleanly broken or severed or
backed off, cut with explosives, drilled on, bent over, covered with
cable or cavings, etc.

368