FISHING TOOLS AND MILLS
We made a total of four milling runs and eight fishing attempts to try to
remove the failed drill pipe and BHA from the hole. Each deployment is
documented in the body of this report. We used both 8-7/8" and 9-1/2"
overshots in our fishing attempts. We used a 6-7/8" basket grapple and
mill control to engage the upset connection on the 5" drill pipe tool joint
(7" OD) on the first attempt and ultimately recovered 497 m of 5" drill
pipe. For all subsequent fishing operations, we used a 5" basket grapple
and mill control to try to engage the tube body of the failed 5" drill pipe.
These attempts were all unsuccessful. We considered using a taper tap
fishing tool to attempt engagement of the inside diameter of the fish, but
this was ruled out for several reasons. First, the failed end of the tube
was crushed where the pipe buckled upon impact with the seafloor. Unless
the milling attempts were successful we would not have been able to
engage the fish internally. Second, the taper tap had no way to circulate to
the bottom of the fish, which was likely firmly stuck in the hole at that
point. If the fish was engaged with the tap, and was indeed stuck in the
hole, we had no jars in the string and no way to disengage the tap. To
prevent sidetracking the fish, we fabricated a wall hook from a 9-1/2"
extension sub and an 8-7/8" extension sub. This would not have been a
problem if the 5" basket grapples and mill controls for the 9-1/2"
overshot had been available, but they were only available for the 8-7/8"
size overshot. In addition, we had some incompatibility associated with
the 8-7/8" overshot hardware that limited our tool make-up. We had one
top sub with a 6-5/8" box and another with an old Hycalog box thread
dating back to the Glomar Challenger days. We really did not want to run
the Hycalog thread because the fish weight was nearly 100K w/o overpull,
and the thread possibly could see some bending loads for which it was not
designed. The bottom threads on the top subs were different, so we ended
up with only one overshot bowl that would screw onto the stronger top sub
and two that would only fit the weaker top sub. In addition, the extension
subs we had would not make up to the stronger top sub. After the first run
the Hycalog box thread was damaged (egged and shoulder damage) and was
very hard to make up on later runs. It was the only option, however, when
we wanted to run an extension sub to try to swallow the fish deeper.
We returned all of the 8-7/8" overshot parts to shore. We felt that this
was the most practical way to solve the thread incompatibility problems
and get things back in shape for future potential fishing jobs.
The following 9-1/2" overshot parts were used on Leg 176 and were either
damaged or lost: One each OF2020 lip guides, one each OF0132 mill
control, one each OF0035 basket grapple, one each OF0140 inner seal, one
each OF0630 9-1/2" Extension Sub, and one each OF2023 flat bottom
guide.
The following list of overshot parts would help out future fishing
operations:
1. 2 each — 9-1/2" OD lip guides for the 8-7/8" overshot
2. 2 each — mill controls for the 9-1/2" overshot assembly
3. 2 each — basket grapples for the 9-1/2" overshot assembly
4. 1 each — 9-m long 8-7/8" extension sub
This would allow fishing the next tool joint instead of trying to fish
a damaged tube. It would have to have heavy duty thread protectors
on it because it would be stored in the riser hold. Also a short
crossover would be good to allow running a 9-1/2" overshot with the
long extension sub.
5.Beef up our inventory of lip guides for both the 8-7/8" and 9-1/2"
overshots.
6.Do away with the Hycalog top subs altogether. This is a really poor
connection for fishing operations. It also requires running a long bit sub as
a crossover, which is also weak because it is bored out for the float and
bearing. We also have the same connection for one of the 9-1/2" overshot
assemblies that needs to be replaced.
7. Sort out the thread compatibility problems with the 8-7/8" overshot
top sub to bowl.
8.Provide a junk mill with an extreme concave face to center a drill pipe
tube better and not allow it to fall so easily off the fish you are
attempting to dress.
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