Activitats

Slickline or electric line operations can be conducted through the jack of a snubbing unit either by rigging up the wireline lubricator on the workstring or screwing an adapter into the stripper bowl and connecting a riser to the work basket.

In both cases normal wireline well control considerations apply, with either a master valve placed on top of the workstring or the snubbing unit blind ram used as a master valve.

6.9.1CONTINGENCIES

In the event of a well control problem occurring during operations, it is the responsibility of the equipment operators in the basket to shut the well in and make safe. The crew chief (chief operator, etc.) is usually working the jack controls and the second man is usually working the BOP/counterbalance panel. This can vary according to crew make-up, breaks, etc.

BOP Sealing Element Leak Ram Type

This can be considered as being in one of two categories:-

• BOP elements changed out as normal routine due to wear

• Leaks around elements occurring unexpectedly

In the case of routine replacement due to wear (the stripping rams are susceptible to this), the inner seals can be changed by closing the safety rams, bleeding off above them and opening the stripping ram bonnets to change the inner seals. It would be normal practice to change the seals in both sets of stripping BOP’s at the same time.

In the case of unexpected leaks, all the BOP’s above the safeties can be repaired by closing the safeties, checking they are holding and then working on the stack. If possible, it is good practice to have two barriers by closing two BOPS' below the one that must be worked on.

Annular

In the case of a leaking annular, it would be necessary to pull back out of the hole, close the blind rams and rig the jack off the well before being able to open the bonnet of the annular. The annular should always start a new job with a fresh rubber and it is indeed a rare occurrence to have to change it during a job. If an annular rubber had to be changed during a job, it would be normal practice to come out of the hole, if at all possible, rather than open the annular with pipe in the hole.

Shear/Seal

In the case of a leaking shear/seal, safety BOP or riser connection, the only choices are to pull back out of the hole and close or plug the wellhead or, if that is not possible to kill the well.

If the well being worked on is low pressure and the safeties will no longer hold pressure, the lower stripping BOP (which has seen little or no use) can be used as a replacement safety until the pipe is out of the hole.

Check Valve Failure

It is not uncommon for the BPV’s to leak if a lot of pumping has taken place. The procedure in this case is to drop the pump down plug and pump it into its nipple. The plug can then be inflow tested and the pipe can be pulled out for a wet trip.

Tubing Pinhole

Prior to using a workstring it should be properly inspected and rattled to minimise the chance of pinholes and scale.

If work strings are not properly cared for, pinholes can develop. Usually pinholes are found when pipe is picked up for the first time. The crews will be looking out for them especially if the pipe quality looks poor.

As the pipe is run the operator can "feel" each tool joint, as it goes through the stripper rubber. As this is the start of a new joint, most operators' first reaction to a sudden egress of fluids out of the top of the pipe is to pull back to the tool joint and back it out. The stabbing valve or other device is then inserted and closed. It should now be possible to bleed down the tubing, which should show that the leak has stopped. Alternately, the tool joint can be run in further until a stabbing valve can be installed and closed.

If the above action does not cure the leak then it must have occurred downhole and the plug must be dropped and seated in the nipple to confirm whether it is the BHA or a tubing hole. If it is a tubing hole, it may be possible to run a wireline set bridge plug that could be used to plug the tubing above the hole and enable the pipe to be pulled otherwise the well will have to be killed.

Any sudden leak occurring before pulling out after washing operations could indicate a washout in the string or BHA (or other problem with the BHA) and will also require the same procedures.

Changing the Stripper Rubber

This is a routine operation, but opens up the topmost containment device, and is performed as follows:-

• Close the annular and lower stripping ram and check they are holding

• Back out the retaining nut and pull out the rubber(s) with a tool joint

• Hang off the pipe and close the safety ram

• Bleed off below the annular through the bleed-off line

• Break the joint in the window

• Install the new rubber by placing on the box and screwing in the pin

• Make up the joint and take the weight of the string

• Open the safety ram and run in to seat the rubber

• Tighten the retaining nut

• Open the BOP’s and RIH

Loss of Power

In the event of a power loss to the snubbing unit, the BOP’s will not be affected as they are on an individual skid with two independent power supplies (e.g. diesel and air)

The worst time for a power loss to occur would be just after having made up a joint with most of it sticking up in the air above the workbasket. If the integrity of the BPV’s was in doubt the counterbalance winch can sometimes be rigged to run from the BOP skid and used to raise a man to install the stabbing valve.