Last year Metrol announced the award of a contract to provide long-term wireless downhole barrier integrity monitoring (up to five years) as part of a client’s well abandonment program.  As the world-leader of downhole acoustic and electromagnetic wireless telemetry,  Metrol have been supplying SENTINEL™ systems for the remote monitoring of shallow and deep-set plugs in platform and subsea wells for many years.

For this campaign a Light Well Intervention Vessel (LWIV) was used, removing the need for an expensive rig and dual bore riser. A client technical authority quoted… 

“The future of rigless P&A is to perform as much pre-abandonment work without a rig as possible. If the subsea XT can be left on the well the HSE case is also increased.”  

The deployment campaign has now concluded successfully and the SENTINEL™ barriers remain in the 11 subsea wells and can be monitored wirelessly for up to ten years. Importantly, it is now possible for the client to plan and possibly delay re-entry of the well with a standard marine riser rather than a dual bore riser. Barrier envelope data provided to the jurisdiction authorities (HSE) allows the client improved resource planning. It is now possible to reschedule rig and LWIV delivery and delay costly permanent abandonment work.

It is the client’s policy to conduct annual visual inspection surveys during the monitoring phase with an ROV, but TRITON™ also allows data collection from the SENTINEL™ system remotely meaning an ROV deployment is not necessary to collect well integrity pressure data and there is no requirement to spend rig or vessel time verifying barriers when returning to the well.

To date, this campaign has already saved the client an estimated $22million by performing as much pre-abandonment work without a rig as possible. A LWIV can perform seven to ten days of pre abandonment remedial work on a well, it can be used to make the well safe, inspect tubing, punch and displace well to kill weight fluid all prior to barrier installation.

When setting two shallow set plugs close to each other, it is almost impossible to know which plug is holding pressure if the lower plug has been successfully tested.  By using the SENTINEL™ wireless system, pressure test data from below the upper plug can be accurately verified. On previous campaigns advanced diagnostics during pressure testing, particularly when setting annulus plugs if tubing has been punched has seen the SENTINEL™ system immediately show if the leak is downhole or on surface/subsea lines.  This can save vessel/rig time when pressure tests start to go wrong.

During long term monitoring, where Metrol are measuring between two barriers, if the pressure increases (on the gauges) this is an indication of an impaired lower barrier.  This data allows a forward plan to be developed in advance of well re-entry and proper risk assessment to be carried out.  More importantly, no unexpected/potentially hazardous surprises are encountered online rig time.

Industry guidelines in certain jurisdictions recommend that a suspended well isn’t left for more than three years without re-entry and/or verification and monitoring of the barrier envelope.  If the barrier integrity is monitored, then a data driven argument can be made to extend the time period before returning with a LWIV or rig. 

For more information on abandonment techniques please contact us.