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Wellhead Removal - The case against removal?
08 January 2020
We are looking at doing an abandonment campaign and we are faced with the challenge from the regulators as to whether the wellhead should be removed. My thoughts are that wellhead removal was something that started in shallower waters where the wellhead would present a hazard to other users of the marine environment and then this requirement just migrated into deepwater water depths.

We can point to the recent GOM change in the CFR's where the BSEE will allow (with the district managers permission) the wellhead to be left in place in water depths greater than 305m. There is also precedent from NOPSEMA where a wellhead was left in place in 190m WD of Australia.

My question to the wider group is are there any good examples out there of where the wellhead was removed during abandonment and then there was a requirement to go back to that well?

Much appreciated 
8 answer(s)
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 471
Join Date: 10/01/05
Major accident Hazard wrt well abandonment?: 
'A fluid and as a worst case a hydrocarbon flow results to surface that would need to be investigated'

'Where UK regs clearly state that an operator must not leave a well such that this event shall result. Everything implemented ALARP to prevent such a fluid flow'

For flow to result there must be a
- > hydrostatics pressure source
- permeability within the pressured formation 
- a flow path. 

Risk Mitigation that could result in an 'Inadequate Long Term Abandonment therefore is simply to assure one follows and complies to Norsok, UK, Regional, Operators standard and regs e.g. that exist.

As Mrs Copland states 'On the UK Continental shelf we have 1000's wells P&A'd some from over 30 years ago. So far, there has been no requirement to go back into any of them

So in this region based on all evident data what has been done to date is apparently working? e.g. 

- All Cement slurries to be lab tested and slurries used further tested and affirmed.
- Pump spacer ahead and behind cement slurry to avoid
- Best practice cementing slurry, displacement, operating practices etc (too many times we see failings here!)
- Verify cement plugs through inflow testing, and/or confirm via tagging/pressure testing (again people generally don't fully understand exactly what best practices are needed / required in certain instances)
- Confirm no  hydrocarbon bearing zones are present in overburden (minimum of two barriers present over each zone)
- Confirm no non- cased/cemented pressured zones present in overburden minimum of  two barriers present over each zone

Wells that are depleted. Wheres there is normal pressure for the first 2-x? thousand feet in a well. Where there are no permeable formations that present a pressure or hydrocardon risk. Where reservoir is depleted present a far lower risk that if.
- > Hydrostatic pressure, peremable formations and/or hydrocarbons greater than hydrostatic pressure exist (Here suitable barriers must be verified and confirmed?)  

Typical inflow test (subsea wells)
1. Make up Top drive and space out drill pipe across the BOP stack
o Test rams and #2 Pipe Rams to be used
o Lower choke valves to be used for trapping pressure
2. Using the rig pump, displace the drill string with 6.6ppg base oil to 60m above the wellhead, taking returns to mud pits. This will create 200psi (deemed required in this case) below the sea water gradient above the plug
3. Close the test ram and pipe ram #2 above the lower choke valves
4. Use the mud pump to pressure up the cavity between the two rams to at least 1000psi via the
lower choke line. Trap and monitor this pressure at the choke manifold - this will ensure a seal
from the riser to the well and eliminate a source of flow
5. Line up the trip tank on the riser with 10.5ppg mud and monitor for gain/loss
6. Open the bleed off line on the standpipe and start inflow test on drill pipe as follows:
o Monitor the trip tank for flow for a minimum of 30 minutes. Record volume recovered versus time
o Allow for initial flow due to fluid expansion
o Acceptance criteria - Zero flow for 30 minutes
7. After satisfactory test results, re-apply 200psi differential pressure down the drill pipe
8. Release trapped pressure between the rams and open rams
9. Reverse circulate/U-tube the base oil out of the drill pipe to original SBM
10. Conduct flow check

What should result is a typical SAFE ALARP abandonment schematic as attached (wellhead left in situ where maritime activities permit)

Note: Only Cement plugs barriers have been used in this well's example afforded preference (Because placing bridge plug and then tagging testing does not guarantee verify or can confirm that the cement plug above such a mechanical barrier (the only approved barrier) is good. Note: We have raised this issues so many times!)

Success in future abandonment and leaving wellheads in situ where regs and lack of seabed / maritime activities in these areas permit.
Documents uploaded by user:
Subsea abandonment.pdf
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 471
Join Date: 10/01/05
One always has to consider the physical hazards and risks presented from each well at the end of its life.
The greatest risk hydrocarbons to surface is diminished because reservoirs are severely depleted and well sealed with multiple barriers to prevent them from plate tectonics recurrences that may happen over tens or hundreds of thousands of years to change residual risk. 
Leaving a Well with most casings particularly the wells foundation strings is a lower risk based option on all accounts. 
We spent a lot of time reviewing all the issues to confirm this from several aspects. Where the conclusion was. Due and diligent abandonment with cement. Verification of dual barriers etc is leaving a well according to regional regulations and standards required. 
Senior Wells & Technology Manager
Oil & Gas Authority (UK)
Total Posts: 4
Join Date: 18/10/16

On the UK Continental shelf we have 1000's wells P&A'd some from over 30 years ago. So far, there has been no requirement to go back into any of them.

Realistically, I don't think an old wellhead and the associated casing would be in a suitable condition that we would trust it to provide seals and  a barrier.

Well Intervention and Integrity Engineer
Total Posts: 3
Join Date: 20/06/19

Good day Team,

I’m no expert on decom, can probably figure out much of it, but here’s my take:

The decom industry is [relatively speaking] very much in it’s infancy, and the decisions taken in these early days will have to last not 20-30 years like many well lifetimes, but hundreds, or possibly thousands of years.

In our engineering mitigation thinking, we ty never to go down a path that we cannot return from if things start go a little off track.

As was mentioned by CasingCutter, re-entering an old well for whatever reason will never be easy if the casing is cut below sea bed.

My bet is, and I doubt I will be alive to see it, that in the distant future, there will be an instance of cement degradation, casing rot, ground shift or similar, and, unless there is sufficient sea water margin of course, a breach will occur.

Now, it’s possible, if not highly likely that by then, any wellhead left in place, and more so the pipe underneath it will be too rotten to be of any use, but at least it’s a locator.

As for platform wells cut below the sea bed, and with jackets removed, well, then it’s not really an option, but at least there should be a big enough target to make it all easier to find.

D&C Project Coordinator / Decommissioning
SPREAD Associates
Total Posts: 35
Join Date: 25/01/16
It is an issue of attitude.  The best one is to leave a location as you found it.  This includes recovering the production casing and setting balanced cement plugs while rotating the cementing string to avoid annular channeling.
.  Each time I was on an abandonment beginning in 1978 there was gas behind production casing so need to perforate with a control system as it is usually bottom hole pressure.  To severe the surface and conductor casing can use explosives and pull with the well head.  If there is a 30" or so structural casing set the severing charge just below the 30"connector so it bells open the latch letting it release as difficult to sever from 13 3/8"/
Pete Thomson
Decommissioning Manager
Baker Hughes
Total Posts: 13
Join Date: 12/12/15

Hi Myles, Jamie, Christian

Just a couple of comments.  The post from Myles relates to my post and responses received back in September / October last year "re-entering old abandoned wells", so you could have a look at that.

A major reason to leave the wellhead in place is for CCS where the well may have to be re-entered to re-cement with slurries resistant to CO2.

Or you could try and make a case for leaving it for future recoil tests of the LMRP and marine riser system.

As an aside to the specific question, different governments have varied views on what can be left on the seabed, being related to the maximum depth for commercial fishing or other users of the sea, and influenced by whichever international standards that country may have signed up to.

The maximum depth for commercial fishing is around 600m.

Accordingly, what is deemed as "deep water" is varied as well.  For example, I believe that Norway works on 600m, Angola's presidential decree has a cut-off of 400m, Brazil is 800m, GoM used to be 800m as well, most of west Africa is 700m, but Vietnam is over 1000m.  With the UK's goal setting regime, depths are not specified.

 It sounds to me that there must have been a good reason for leaving wellheads in water depths of 160m or 190m - that's appears to be a little too shallow!!

Hope this assists

Well Abandonment Manager
Total Posts: 10
Join Date: 30/09/13

Talking specifically about subsea wellheads - a few years back we were asked to attend a meeting with an operator to offer up how 1) we can find the exact locations of previously abandoned subsea wells and 2) reconnect to the casings and conductor previously cut at 15' below seabed.

The reason for re-entry was never disclosed to us. Obviously a difficult task to reattach.

We have just finished a P&A project in Malaysia where the wellheads were left in place after reservoir and intermediate abandonments and that was around 160m water depth.

Total Posts: 3
Join Date: 14/01/18

can't give you a direct answer to your question - the only reason to go back to an abandoned well is if the well is leaking...but that is not a good reason to argue with the regulator.

Some other examples:

- the regulator in Egypt specifically requires operators to leave the wellheads on for later re-entry and or production purposes (although that has never happened)

- in Norway we have to remove them, however we are allowed to leave them in place if covered by a so-called "net guard" to protect the fishing nets.

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