Hangoff Procedures During Bad Weather

Whilst 'Waiting on Weather' it might be necessary to hang the drill string off from the wellhead or BOPs. In severe cases, it might also be necessary to disconnect the riser from the BOP stack. The decision to 'hang-off should be taken to allow sufficient time for the bit to be pulled safely into the casing shoe. A natural tendency for the driller to pull up too quickly could perhaps induce swabbing and a possible kick situation later.

The preferred method to hang-off the string is to use a special hang-off tool which supports the pipe in the wellhead. It consists of a fluted hanger that is designed to land on the wear bushing, casing hanger or seal assembly, a slick joint around which the pipe ram(s) can be closed and an upper sub containing both a coarse left hand thread and a drill pipe thread box. Each hang-off assembly should be appropriate to the particular wellhead (BOP) in use so that once it is in place and disconnected the pipe ram(s) can be closed round the slick joint and the shear rams can be closed above the top sub.

For some wellhead systems, only one fluted hanger is needed and can be run whatever size wear bushing or casing hanger is in the wellhead. Other systems require the hanger to be changed according to the size of the last casing string run. Various spacer subs appropriate to the distance between the hang-off point and the shear rams might also be required.

In order to provide additional safety, it is usual practice to install an inside BOP (or inside BOP with an open Kelly cock underneath it) one joint below the fluted hanger.

The general procedure for running a hang-off tool is as follows, assuming drilling has been in progress:

  1. Pull the bit into the casing shoe plus the distance from the rotary table to the wellhead.
  2. Install the inside BOP and make up the hang-off assembly to the string.
  3. Run the tool to the wellhead and land on the bore protector, compensating for the weight of the running string.
  4. Turn to the right to release the running sub from the top sub.
  5. Pull the running sub above the shear rams. Close both pipe and shear rams and circulate the riser to seawater (if time and conditions allow).

By the time step 4 is reached, the rig could be heaving quite a lot so if possible the Kelly/Top Drive should be used to release the running sub. It is good practice of course to have the hang-off assembly (appropriate for the wear bushing size) permanently made up and stood back in the derrick ready for use.

  • rilling S Well Services Training
  • rilling S Well Services Training

If it was necessary to unlatch the lower riser package, the procedure to recover the string would be:

  1. Re-latch the package onto the stack (check by taking an overpull) and test the integrity of the choke and kill lines by pressure testing again the outer failsafe valves.
  2. Run the retrieving tool (possibly with a stabiliser for centralisation) to above the shear rams.
  3. Circulate the riser to mud.
  4. Open the failsafe valve against the choke to check for any pressure trapped under the rams.
  5. Open the shear rams and stab into the top sub, turning to the right until the required amount of torque is shown to indicate that the drillpipe thread is made up.
  6. Circulate/condition the well if thought necessary, then pull the hang-off tool and redress for use the next time.

In the event that there is pressure under the rams, this could be caused by gas swabbed into the well whilst pulling to the shoe and which had migrated whilst waiting on weather. If so, it might be possible to safely remove it by circulating under the ram — down the kill line and up the choke line. The alternative would be a 'top kill' or stripping operation.

Barite settling out from the mud and causing a reduction in hydrostatic can also be a problem during the prolonged periods of waiting on weather.

In the event that a very severe storm blows up without warning, there might not be sufficient time to pull the bit into the casing and use the hang-off tool. If this emergency arises, the bit should be pulled just the distance from the rotary table to the stack so that one of the drillpipe connections can be broken and made up again only chains tong tight. The string is then run again and the loose tool joint landed carefully on the upper pipe ram. With the weight slacked off, the string is turned to the left to back it of at the loose connection. The other pipe rams, shear rams and ram locks (if applicable) can then be closed.

Note that in this case, it might be better not to run an inside BOP since it is very likely that the string, being hung off in open hole, will be found to be differentially stuck and wireline backoff operations could be necessary. If the string does have to be hung-off in open hole, then the hang-off tool should not be used at all.

As an alternative to a special hang-off tool, it is possible to use a joint of drillpipe with a square shouldered upset on it which can be landed on the pipe rams. Such a method is satisfactory but is not preferred to landing the string in the wellhead.

When running long strings of casing, it is always advisable to have a suitable casing/drillpipe crossover available to enable the hang-off tool to be used to hang-off the casing string if necessary.

Another method of hanging-off the string is to support it from a retrievable packer set in the casing just below the wellhead. To do this requires more time than if a hang-off tool were used but in some circumstances, it might be the most suitable means available.

In addition to the retrievable packer (which seals off the annulus) a special storm valve is used in the string. This is made up into the packer and serves both as means of releasing the running string and sealing off the bore of the drill pipe. The valve, which is a sleeve type operated by left hand rotation.

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Responses

  • odo
    How to hang off drill pipe in a bop stack?
    8 years ago
  • frank schiffer
    What are hang off drills in oil fields?
    3 years ago
  • ray
    Can you hang off a drill string on a vbr?
    1 year ago
  • Anna
    How to calculate hangoff weight on pipe rams?
    1 year ago
  • teija
    What is the function of hang off bushing on rotary table?
    1 year ago
  • maura
    How to unlatch a drilling riser?
    11 months ago
  • rocco
    Can you hang off pipe with vbr ram blocks?
    8 days ago
  • bildad goodbody
    What does shear the drill pipe after hangingoff mean?
    9 hours ago

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