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Preventing and removing hydrates at BOP wellhead or LMRP connector
16 May 2015
Could you tell me how to prevent hydrates at the BOP wellhead or LMRP connector as well as removing hydrates that prevent from disconnecting.

I know that mud mats are one way to prevent hydrates around the BOP.

Thanks,

Soren
7 answer(s)
stevedev
Drilling Consultant
SPREADAssociates
Total Posts: 36
Join Date: 11/02/09
Your wellhead connector should have a port for the ROV to inject a bit of glycol on each dive. If you see hydrates, they can be jetted away by the ROV pumping seawater at them. Injecting glycol into the connector should also help.
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 343
Join Date: 10/01/05

Soren,

See attachment. This well illustration likely many other, ran mud mats as a 'hydrate deflection barrier'. Thus in this case, it disnae work!

What is used as per attachment (as extracted for  IADC deepwater well control guidelines) is a sealed system (like a mud mat).

However in certain cases primarily as this does not address the problem, (preventing hydrate migration at source) the same scenario will  likely result. i.e. well integrity failure that results in a 'channelled flow path' for hydrates to travel. 

As per other posts therefore 'prevention is thus better than cure'. e.g.

Siting well in safest place, good jetting procedures, running flush pipe or thinner OD connector, minimising soil disturbance can prevent hydrate percolation via external conductor.

Via conductor and surface string, good drilling practices to avoid fracturing well or transmitting a fracture at some point (is in my view the most common reason why hydrates then percolate to surface), therefore delivering a good wellbore, (drilling, tripping, casing and cementing), and fully understand pressure regimes, where cementing is most critical and where centralising casing, good cementation to surface etc etc are a selection of further best practices to prevent vs cure.

If hydrates form then surely (something has failed to cause this?) and as posted in this discussion, then hydrate seals, injection port, and daily dive by ROV to remove, is what has to be expedited to prevent connectors getting stuck etc.

Documents uploaded by user:
hydrates on SSBOP_ mud mat included.odt
RuariTruter
SPREADAssociates
Total Posts: 17
Join Date: 17/09/07

Soren

Look at the major enablers of Hydrate formation (5 off the top of my head), with the most obvious being Gas.  A Mud Mat alone does not work, you need to isolate / connect it to the 36" (Or whatever).  Secondly you need to make sure your isolate your HPWHH, with cement & locking it down.  Then you need to make sure you have a hydrate diversion seal on the connector, to prevent gas getting into your connector.

No gas, no hydrate.  This is a Good Thing.

If you do have gas, and the correct environment for Hydrates, this is a Bad Thing.

So what do you do?

Initially, as prevention of hydrates, you pump Glycol into your connector cavity.  This is 'relatively' easily done by ROV.  It is often done as a precaution.  You can also jet the stack to remove hydrate from the outside.

Unfortunately Glycol is more of a prevention rather than a solution. It is not very effective in removing Hydrates.  What you need to remove Hydrates is Methanol, which is nasty stuff.  This is a Bad Thing.

But you pump Methanol, which hopefully removes your Hydrate.

One small thing to be aware of. If you suspect hydrates (Pressures while pumping Glycol, bubbles at seabed etc), do not function the connector, as this merely compresses them.  Which makes them even harder to remove (Even with Methanol), and is generally considered a Bad Thing.

Cheers....Ruari

rpellow
Co Rep
DONG Energy
Total Posts: 4
Join Date: 20/02/14
As mentioned, methanol is the only thing that works to remove hydrates.  It's not a nice thing to have onboard, you have to keep it in a bunded area and you need a lot of salt surrounding it - because it burns with a completely colourless flame - and the salt will burn with an orange one.  So if you see the salt burning you have a major problem.
GeorgeCheyne
Assistant Operations Manager
Stena Drilling Ltd
Total Posts: 1
Join Date: 24/01/15

Hydrates at the connector can be prevented by injecting Glycol at regular frequencies using the ROV to inject and displace the volume.  Glycol is no use for dissolving hydrates already formed and Methanol can be employed to deal with it.  Your geographical location may have an impact on whether or not Methanol is available off the shelf.  Prevention is better than cure so go with the Glycol injection.  

gausingla
Drilling Engineer
Myspread Users
Total Posts: 1
Join Date: 16/05/15
There are generally Glycol injection lines in the BOP. Glycol can be injected from surface through these lines. Gycol injection guidelines/procedures can be found in the Drilling Contractor manuals. Remember here we are talking about preventing hydrate formation in side the BOP and inside wellhead area.
To prevent hydrate formation outside, below mudmat, need to inject glycol with the help of ROV time to time.




RobinWatt
Subsea Engineer
Applied Drilling Technology International
Total Posts: 6
Join Date: 11/02/10
From what I remember, deepwater H-4 connectors can be plumbed to to the BOP to provide a ROV hotstab where glycol can be injected and washed through to a bleed port on the opposite side.  This clears any hydrates surrounding the internal mechanical components.
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