Temporary suspension options (Cased hole retrievab
14 July 2008
What's the groups experiences with mechanical bridge plugs used for
temporary suspension ( ~2 years).
The well is in the Central North Sea, normally pressured, suspended
in 9 5/8 casing with kill weight fluid and a 500ft cement plug (set
on a drillable retainer) below.
The cement plug is there in case the suspension period extends
beyond the 2 yrs expected....
The retrievable plug will act as the 2nd temporary reservoir barrier
as per UKOOA guidelines.
The first option always mentioned is the Baker GT plug, but
obviously this is the costly one....
Has anyone used a Weatherford DLT with storm valve or a Halliburton
RTTS for longer term suspension?
What about the Halliburton Isolator or model 3L bridge plugs?
Any other retrievable options to consider (with decent case
I have only really used the GT plug for long term suspensions.
I guess now that they have the market, the prices are heading up.
Not any experience of the other plugs in a long term mode although I
am sure they are all much of the same.
The attraction of the GT plug was always its fishability compared
with some of the others should the worst happen and you leave it in
the hole. I think it is also the better one to have to mill up if
the real real worst happens as most of the others have rings that
you would spin on for years.
I hope this helps
Well Team Leader
We did not use RTTS for that long period as there is a risk of
getting stuck and can not retrieve it, I believe the drillable
bridge plug and cement is the right way to go.
bp Gupco - Egypt
I believe the Norwegians may be in a position to supply
alternatives to the options listed below as a great deal of work
has been done on V0 suspension plugs and lower rated ones too. A
good place to start to avoid the majors would be Pii in Stavanger.
Caledus - Aberdeen
If you have a cement plug that is tagged/tested (primary barrier)
with a mechanical plug (that was also tested) to boot. This could
And with a fluid column (the second barrier) above, that is inside
casing, in a normally pressurised well, then what else do you need?
To keep things simple setting a further cement plug is far better
than any mechanical device.
8. REQUIRED STANDARD FOR SUSPENSION
8.1 Types of Suspension
Wells can be suspended for various reasons and can be classified as
- Short Suspension: for removal of BOPs, batch drilling of
(tophole only, or partially drilled wells down to any depth), to
accommodate pipelay activities in the field, etc.
- Long Suspension: E&A wells that are considered for field
Suspension of E&A wells should be the exception rather than rule.
Proposed suspension period of over 18 months should be specially
justified and in compliance with the DTI and UKOOA requirements
(PON5 and UKOOA Suspension Workgroup - Recommendation 1.2)
8.2 Principles of Suspension
a) Number and Type of Barriers
In common with the Abandonment guidelines, two Temporary
Barriers are required for isolation of Hydrocarbon Bearing or
Overpressured Permeable Zones from surface/seabed. A single barrier
is acceptable for normally pressured water bearing zones. It may be
argued that kill weight fluid will constitute a Temporary Barrier in
certain circumstances. This may include occasions when a full column
of fluid can be monitored and maintained. However, in general a
Temporary Barrier should consist of a pressure tested mechanical
device or good cement as defined and verified in Section 5.4.
Even though Temporary Barriers may be used for Suspension
purposes, it is advisable to consider Suspending a well such (with
Permanent Barriers), that only the wellhead needs removing from the
Suspended well, in order for it to be permanently Abandoned.
b) Well Re-entry Considerations
Since a Suspended well will by definition be capable of
being re-entered, the Suspension must be carried out so that the
well can be re-entered and secured using pressure control equipment
without compromising the barriers in place. Placement of the Second
Barrier, if required, should consider the consequences of potential
failure of the First (deeper) Barrier. Furthermore, consideration
should be given to set the top plug sufficiently deep, in order to
facilitate later Abandonment of the well.
8.3 Acceptable Barriers
The Operator should assess and define the type and
suitability of any mechanical barriers. Due consideration should be
given to the anticipated period of the Suspension, the subsurface
environment and the type of well.
Pressure tested casing is an acceptable barrier to flow into
8.4 Verification of Barriers
Any First Barrier should be pressure and/or inflow tested.
Any plug which may subsequently be used as a Permanent Barrier, i.e.
the well may not be re-entered, should meet the requirements of the
Abandonment guidelines in Sections 4 and 5.
In response to the question raised .. why mess about with GT plugs
or similar for such a long period of time - expensive no matter who
you rent from.
Have you looked at what it would take to abandon the well
permanently in the event that the 'Management' change their mind and
decide to abandon and not to reuse the well at a later date? If so
set a second cement plug to avoid using a GT plug or similar; this
2nd cement plug might also allow the well to be left as a category 1
Even if the well is definitely going to be re-used; I would still
prefer to see a cement plug as opposed to a GT plug especially over
that length of time.
We have received the following reply, from someone who would prefer
to remain anonymous ..
"The Baker GT Bridge plug is generally used for long term (>1 year)
suspension because the manufacturer has documented test data
(evidence) to support/demonstate that it retains its integrity for
a reasonable suspension period in downhole wellbore conditions.
From memory I think Baker did this work for BP to suspend its wells
in Scheilhallion/Foinaven. Given the HSE attention afforded this
development (particularly environmental concerns) they (Baker and
BP) had to demonstrate that the two mechanical barriers they
selected were fit for purpose for the maximum suspension period
I do not know of any one using a storm/hurricane packer or RTTS
mainly due to concerns in retrieving such a device after some
considerable time frame. Milling out such a device would not be easy
on re-entering a well.
The problems associated with some bridge plugs would be the risks
associated with trapped pressure below them and how this could be
monitored/addressed before releasing the slips on drill out. I have
heard of such plugs set near surface coming up the hole! Obviously
designs vary and a design could be selected where pressure
communication to the trapped volume below the BP can be achieved
prior to drilling out/releasing the slips.
I think it all boils down to being able to demonstrate that what is
planned reduces 1) the risk of any leakage from the well during the
planned/unplanned suspension period and 2) reduces the risks to
those who have to re-enter a suspended well to ALARP levels.
I hope this helps......... "