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P&A offshore wells
03 December 2020
My apologies, if my question is  very basic one.

But I was wondering what happens to the permanently P&A offshore wells,  especially the old wells,  and how are their integrity  is monitored (and how frequent)  to make sure the well barriers in place are still doing their job , for example, no leakage to the surrounding environment

9 answer(s)
Drilling Mgr
Philippine Geothermal Prodn Co
Total Posts: 1
Join Date: 12/12/20

Prior to retirement I was involved in global P&A and had the chance to evaluate different country standards.  Also had the chance to review and input standards to countries that are still developing.  Like Gordon mentioned, different countries have different standards.  In the absence of existing regulation, as the company I was working for has global barrier standard - our standard will be followed.  Our global standard is risk based and as a general guideline..on areas our standard is not very specific .. risk assessment is recommended.

Hope the above helps

SPREAD Associates
Total Posts: 6
Join Date: 11/02/10
Many thanks for sharing this great world wide overview, Gordon.
Very valuable and very helpful, and important for our company when it comes to strategy versus technologies and methodologies we work on for rig-less P&A.

PS: We were recently challenged by a North Sea operator that observes gas leaking from a seabed well entry, where the wellbore was permanently P&A´d some time ago. Now we are outlining a plan and a technology for containing the leak within the wellbore, where we are basing this on using bismuth alloy (melting metal).

Technical Director / Trainer
SPREAD Associates
Total Posts: 14
Join Date: 31/03/20
See attached overview of worldwide regulations, which does touch on Post Abandonment guidelines
However as you can see from the summary everywhere has a different take as well as interpretation of the rules.

Hope i have not confused you further

Documents uploaded by user:
Overview of Regs.pdf
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 502
Join Date: 10/01/05
Lots of good posts and best practices to consider.

The UK and Norwegian reg's are quite clear.
'Nothing can ever leak to surface'.

- UK Oil and Gas P&A guidelines. rev 3
- Norsok D-010 rev 4 well design and integrity regs,
- BSEE regs
- Best cement plug practices.
- New Technologys that exist BisN etc
Offer safe, effective and efficient abandonment solutions for onshore/ offshore wells if hazards/risks within each well during final P&A are fully comprehended mitigated and addressed.

Where as has been stated a 'hazard/Risk assessment approach' is needed because wells are rarely classed or exist as exactly the same.

Key well factors to further consider in offshore P&A.

- In the first xxxxm of offshore wells, all formations are both porous and permeable! So there could be a problem as all permeble formations must be safely abandoned!
- If normally pressure exist, a low risk exist.
- Is abnormal pressure (hazards/ higher risks) exist? these must be mitigated with necessary added barriers, assured in place.

- During abandonment this then sets up the discussion of whether it is better to leave structural casings / wellhead in place (with more barriers) or cut and pull casings to potentially now have less barriers and potentially increase risk.
- And whether wells need to be checked, if at all? Risk based? 

Commonly they are not. Low risk wells.
High risk wells, may need to be checked periodically.

- With intermediate and production strings again if permeable, abnormally pressures zones exist are not confirmed or verified as having good cement.
- Potential risks exists across all permeable zones to be further assured against in abandonment.
- And why one verified and one further confirmed two barrier assurance is required.
- Wells may be several depleted, and despite being permeable there is no pressure risk. These wells are low risk.

- vs live exploration, appraisal or other wells to be abandoned for what ever reason. (present much Higher risk)

- Wells that have existing or potentially well integrity barrier issues? Normal P&A methods may not work, where new technologies such a Bisn etc are needed and being used to safely abandon wells and reduce all risks to ALARP

- Technologys that are being validated in certain areas.

- Verification of all abandonment barrier, notable cement plugs via a inflow test is the most preferred method, when/if practicable to do so.
- Otherwise other confirmation methods exist. (Volumetrics, surface cement samples, tagging pressure testing.)  

- If a bridge plug or mechanical barrier is set below and a cement plug then placed on top. Cement plugs cannot be verified. So a low but potential risk will always exist in such cases. 

- In some offshore areas where no maritime or fishing activities exist wellhead can be left in place.
- In some offshore areas wells are left in situ. Trawling caps may be fitted or not. Globally rules and regs are not the same.    

In truth, there are so many variances, that a one suit does not fit all. (Regulators and governing bodies should appreciate this)

Despite all best intents, there are wells that inevitably do not meet all required P&A best practices / hazard/risk base approach criteria. That will probably be very difficult and expensive to fix.

In view of this we always try and assure in each case we 'do the right things' and 'get things right first time' during P&A to assure no flow can reach surface ALARP.
Drilling Consultant
Total Posts: 3
Join Date: 01/07/19
Our practice is to run an ROV inspection once a year to make sure the abandoned wells are not leaking. But AUV will be a cheaper and faster solution especially at the oilfields where you have multiple wells. Other cost-efficient solution is to install a sonar that will detect the sound of the leakage. And as a safeguard for the integrity of well is to install a protection structure with anti-trawl feature to prevent the well being damaged by marine operations and fishing activities.
SPREAD Associates
Total Posts: 6
Join Date: 11/02/10
Monitoring an abandoned offshore well, even after the wellhead have been cut and removed, is fully possible. 
We can mount a device on top of the well entry, where this device detects and measures leak rate from the wellbore, and this information may be transmitted to a nearby installation, to a vessel, etc.
A device can even collect leakages, where the fluid from this leak (not at least if its oil) can be safely retrieved. Hence, the wellbore can be monitored and it can be verified if the situation improves or gets worse.

It may also be possible to sample the leak to analyze where it´s coming from. Sometimes it may only be gas generated from the upper end of the borehole from the abandonment process, where this "leak" will suspend after some time without causing any reasons for concern
Drilling Supt
China National Offshore Oil Corporation
Total Posts: 18
Join Date: 24/09/09
that's a good question. after the well is permenently abanded, never do any monitoring, it is difficult infact. So before we P&A the well, we shall do a integrity acessment, malke sure the well in good conditon. after P&A, the well can be has no leakage to the seabed.I think some times the subsea wellhead can be left in the seabed if no influence to the navy or other marine activities. Does any body know is there any regulations of subsea well P&A? or any good practice of  P&A a subsea well , share with me, much appreciation.
Wells Mgr - Wellspec
Total Posts: 48
Join Date: 23/03/16


Permanently abandoned offshore wells are generally not monitored. The challenge with these wells is generally that most of the time the wellhead has been cut below the seabed and finding the well and monitoring becomes complex.

If there are problems with abandoned offshore wells, they are generally discovered due to escaping gas or escaping oil which is spotted at surface or during some other survey.

Currently working on a leaking subsea abandoned well in Africa, where (luckily) the wellhead was left in place. Gas was discovered during an ROV survey of a nearby well. Re-entering an abandoned well and finding the origin of the leak source and isolating the zone is incredible complex and expensive.

Connecting a rig to an abandoned leaking well and safely drilling out cement plugs which potentially can have gas below them takes a great deal of planning. Once connected and re-entered, finding and isolating the producing source zone will be the next challenge. Sometimes these zones are thin gas producing sands that were often not even seen when the well was drilled. These zones can be leaking from annuli behind casing strings where direct access is not possible.

It is critically important that offshore well abandonment is done correctly. Re-entering an abandoned well to fix a leak will be very costly and there is no financial return on that investment. It is important that well abandonment is done right the first time.

Workover Engineer
SPREAD Associates
Total Posts: 21
Join Date: 01/08/18
Hi Raed,

Good question.

Here are my suggestions :

A. For how long shall be monitored

It can be as low as 0 and as high as 10 years

Use the practical tools (risk-based analyse, in place local and international legislation)


Risk based analyse shall include:


-         A record of issues during the life of the well (no significant issues might not require any monitoring to be carried out post-decommissioning)

-        The presence of at least one operational well (the full suite of monitoring is still undertaken at the site and shall stop only when the last well at a site is decommissioned)

-        A record of the post-decommissioning pressure test (if tests passed the likelihood is that an adequate seal has been achieved for short to medium period of time)

-        Impact of post decommissioning activities on well integrity  (new well accidentally drilled through a decommissioned well, the wellbore can be cut at a critical depth horizon due to natural or induced1 fault re-activation)

1 High pressure injected fluids into the formation

 Fault reactivation assessments and micro-seismic monitoring should be considered best practice for shale gas wells

-        Understanding the long-term performance of materials2 used to plug and abandon wells, particularly where there are hostile chemical environments (e.g. H2S and CO2), or in high temperature wells

2 Corrosion of steel well tubulars / joints and eventual chemical breakdown of the cement

It shall be considered that adverse environmental effects from these slow processes may not be seen for many decades or even hundreds of years.


Local environmental regulations might require regular monitoring for a specific period of time.

B. How often

I will follow also the risk assessment approach

I hope this is useful for you.


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