Ever seen the effect on the seabed of a 300t BOP dropped from a rig? Marin's George Stroud, aka Boris or the 'Deepwater Red Adair', has and he likens it to a carpet tack being driven into the floor with the force of an impact hammer. The subsea excavation specialist shares his company's learnings to date from 25 successful lost asset recovery operations – including the retrieval last year of a BOP and lower marine riser package offshore Brazil.
The loss of an asset such as a blowout preventer from a rig or vessel can lead to significant operational and financial consequences if no recovery strategy has been put in place. That may appear to state the obvious, but consider this: only around one in ten offshore operators takes a proactive approach. The rest leave it to chance and should the worst happen have no idea how to launch and see through a successful asset recovery. There is instead chaos – the instinctive human response in an emergency is to take action, to do something in a bid to restore the status quo, and all too often an already complex recovery can become even more challenging.
The Marin Subsea team – part of the Marin Group of subsea service companies – has seen this happen on numerous occasions over the past 20 years, and has frequently been called in to unravel the complications of a DIY rescue attempt before going on to complete the actual recovery. In the process Marin has developed the world's only specialist dropped BOP and lost asset recovery service, with a track record of more than 25 successful operations.
The company's capabilities are based on a mix of extensive drilling experience at senior level and its status as the pioneers of mass flow excavation and claycutting (OE December 2010). Understanding the subsea environment from every perspective relevant to asset recovery and possessing the right resources – in terms of equipment and people – enables quick response in an emergency.
Marin Subsea's experience — much of it in challenging locations at depths of up to 2060m and in live fields – has shown most clearly is that the successful recovery of a BOP, riser, template or other asset, is always linked to meticulous planning and implementing a tried and tested procedure that involves identifying the precise tooling mix needed and assigning clearly demarcated roles and responsibilities, both to its own team and those of its clients.
As soon as Marin Subsea is alerted, its first priority is to get from the client as much information as possible and to advise on what should be done – and what should be left alone – before the team reaches the installation. At this stage Marin Subsea starts putting together a basic recovery tooling package, drawing up an outline plan and allocating up to six team members to the operation.
To illustrate the complexities involved in this type of work, take as an example a BOP dropped from a rig. This asset, up to 14m tall, 4m square and weighing more than 300t, may be buried some considerable distance beneath the seabed and also be lying at an angle. When a BOP goes into the seabed, the effect is analogous to a carpet tack being driven into the floor with the force of an impact hammer. As the BOP enters the impact site, there is therefore immediate disruption, with the soil becoming mobile and almost fluid before pushing back with a bow-wave effect.
This can sometimes mean that – despite the enormous impact – there is little sign of the crater in which the asset is now lying. Furthermore, the riser or other equipment that should logically lead to the BOP may also have become buried or detached, or buckled and doubled over.
Once on site, Marin follows a recovery sequence that it knows from experience produces the best results most rapidly, and takes full overall control of the operation from start to finish.
Among the initial elements needed to do this effectively are:
The equipment used to complete a recovery varies from operation to operation, but typically will include:
Once the dropped object has been located, there will be a number of challenges to overcome before it can be pulled to the surface and covering all possible eventualities forms part of the Marin Subsea team's pre-recovery planning procedures. The actual excavation may, for example, involve having to deliberately break down the walls of a very deep crater before re-excavating to create a wider crater with shallower, safer walls.
Debris frequently has to be separated from the asset – or assets – being recovered, and this can become particularly complex if a BOP is for example lying at more than 10° from horizontal.
In this situation, gaining access for lifting is also difficult — where the BOP has landed in a vertical position, it is often possible to stab straight into the top but not when it is lying offset. Where recovery slings were fitted before the asset was dropped they are sometimes inaccessible or found to be damaged, and very accurate excavation may then be needed before new lifting gear can be attached. This in itself is fraught with potential dangers – if the wrong type and strength of sling is used, or the ROV positions the sling even slightly inaccurately, the asset can easily be dropped again.
Pulling the asset to the surface is a complex process requiring meticulous organisation and often involving very rapid decision-making: almost always equipment has suffered damage impossible to identify subsea and judgments have to be made about the likelihood of it failing while being lifted from the seabed, through the splash zone, and onto the installation.
Post-recovery, the Marin Subsea team advises the client on its observations. It does not carry out inspection work but its extensive experience means it is well placed to highlight likely impact damage, including to a BOP's operating and sealing systems, rams, and upper and lower annulars, and flex joint.
Marin Subsea numbers major drilling companies among its contract asset recovery clients but the bulk of the recoveries it conducts remain those that come to it in situations where an operator has lost an asset, quickly realises it does not have the knowledge, expertise or equipment to go it alone, and needs urgent help to retrieve it. OE
About the Author
George Stroud is CEO of the Marin Group of subsea service companies, of which Marin Subsea is a member. He started out in oil and gas as a roustabout, rising through the ranks to become a drilling superintendent before switching direction to join forces with Nick Sills – now Marin Group technical director – and focus on developing mass flow excavation and claycutting systems. Stroud has been involved in asset recovery for more than 20 years and, as leader of the Marin Subsea team, says he is 'personally on call 24/7/365'.
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