Rising to the subsea challenge

With the increased complexity of today’s subsea production systems giving mooring solutions providers much to think about, Viking Moorings chief executive Wolfgang Wandl discusses how his company is rising to the challenge.

The global mooring industry today is facing significant logistical and safety challenges in the securing of offshore installations.

With operators and rig contractors opening up production in deeper waters, rig numbers increasing, and operators’ continued need to manage costs and move rigs quickly and cost effectively (with a typical rig moving up to 10 times a year), mooring solutions providers are facing more challenges than ever before in meeting operator needs.

From taut leg mooring systems, with high vertical loads on the anchors and a reduced mooring pattern radius, to catenary systems, with a larger mooring pattern radius, higher weights and lengths, and no vertical load on the anchor, and the emergence of pre-set moorings, mooring solutions providers have much to think about in supporting today’s offshore installations.

Songa Delta

Subsea complexity

Take the complexity of today’s mooring operations and the subsea production systems around which they must operate. The typical mooring spread for a semisubmersible rig is between eight and 12 anchor lines, all providing a potential threat to existing infrastructure as well as being costly in terms of deploying the necessary number of anchor handling vessels (AHVs). We must also keep in mind accommodation rigs and FPSOs.

Subsea, there are many more potential pipelines and obstructions to be aware of. For example, when located at Øseberg on the Norwegian Continental Shelf in 102m of water the Songa Delta semisubmersible drilling unit’s mooring lines were up to 2km long and included wire ropes, fibre ropes, buoys and chains – all able to cause significant damage to the area’s densely populated subsea infrastructure.

Another challenging offshore installation Viking has been involved in is the Valhall field in the Norwegian North Sea. That complex today consists of five bridge-linked steel platforms connected to a number of subsea satellites and with live seismic also taking place.

Mooring solutions providers need to be very aware of these subsea obstacles, as well as addressing the issue of cost balanced against the importance of safety. With AHVs costing up to $150,000/day, unpredictable factors such as the weather remain a constant challenge and the 2007 Bourbon Dolphin tragedy is still fresh in people’s minds.

Today’s mooring solutions on offshore installations must ensure that there is no damage to existing seabed infrastructure. They need to be smart and innovative, with the ultimate goal being to ensure that the rigs are moved and secured as seamlessly, cost-effectively and safely as possible. How is this being achieved?

anchor vesselAnchor handling vessels can cost up to $150,000 a day.

Pre-set mooring

One of the most significant developments in mooring offshore installations is the rise in pre-set mooring. Establishing the mooring infrastructure – anchors, chain and wire or fibre rope – in advance of a rig’s arrival, with surface buoys attached for quick recovery, brings with it a number of benefits.

It can ensure greater precision and control over the positioning of the mooring solutions around existing infrastructure. Vikiing has deployed anchors more than once in the same field many times. Other benefits include the overcoming of depth limitations, lower NOx and CO2 emissions, and reduced costs with one AHV able to install each leg of the pre-set mooring system.

Pre-set mooring also enables a more strategic approach in supporting offshore installations. Targets areas can be mapped out and mooring solutions put in place months in advance, with the weather and other unknown variables tackled more directly.

If pre-set mooring can take place weeks before required, for example, situations such as spending 33 days at sea in high waves on an AHV which is unable to return to port or install the mooring (as was the case with one of Viking’s teams recently) will be a thing of the past.

And the potential lost revenue can be staggering. In the example above, if four vessels are at sea at say $125,000 a day, the cost is $16.5 million just to start with and this doesn’t include the lost future revenue from the downtime of the rig.

It is against this context that Viking considers pre-lay mooring to be central to the future of the offshore mooring industry. Today, the company has pre- lay mooring systems laid throughout the world and a future where the mooring infrastructure around target fields remains ever present with operators linking their offshore installations into the pre-set mooring whenever required looks increasingly likely.

Anchor handling

Pre-set mooring is just one means of better optimising the use of AHVs. With anchor handling operations sometimes taking up to 10% of the total cost of offshore exploration wells, making the anchor handling and retrieval process more cost effective and flexible is central to the future of mooring offshore installations.

There are significant challenges to anchor operations as well. Take the Baobab oil field, located 16km off the Ivory Coast, with its estimated reserves of 700 million barrels and recoverable reserves of 200 million barrels. This field, with water depths of over 1200m, seabed obstructions, a steeply sloping seabed and soil instability, presented a significant challenge to anchors. In this case, Viking supplied a taut leg mooring system with the rig skidding 900m between drill centres.

One solution expected to make anchor handling more effective is Vryhof Anchors’ new Stevtrack Anchor Data Acquisition System (OE August) which Viking is now installing on some of its anchors for drilling rig operations.

The Stevtrack systems works through a transponder unit on the anchor which communicates with a setback monitor on the AHV, displaying real-time data on variables, such as roll, pitch, drag length, penetration depth and pull-in force. The system can also confirm when the anchor is positioned correctly on the seabed and avoids the need for anchors to be reset, saving both time and money. The result is a real-time overview of the entire anchor installation process on the seabed and faster anchor installations in real-time.

For all the recent technical developments in the oil & gas industry, the anchor retrieval process is surprisingly crude, often relying on grapnels, which are used to retrieve chain and wire from the seabed and can cause a significant threat to pipelines and other subsea infrastructure.

To this end, Viking has developed the Spin Buoy. With this system a submerged buoy can be brought to the surface using a coded acoustic signal. The signal will release the buoy, while the hydrodynamic fairing forces the buoy to rotate, paying out rope. The rope is then connected to the rest of the mooring line making it easier to retrieve the anchor.

The result is time and cost savings on retrieval, reduced risks of any damage, and improved safety during mobilisation and demobilisation.

authorWolfgang Wandl has a civil engineering background and played leading roles in the construction of major oil and gas platforms in Norway and Canada with companies such as Strukturas, NRS and Gleitbau. He joined Viking Moorings as its Norway country manager in 2006 and stepped up to CEO in July last year.

Both systems were tested at the ONS show in Stavanger this August where representatives from E&P operators and drilling contractors, the Norwegian Maritime Directorate, the Petroleum Safety Authority, and partners such as DNV were able to see these new solutions in action.

The last few years have also seen a focus on dynamically positioned rigs which don’t require mooring anchors, but rather are kept in position by computer- controlled thruster propellers.

While the reduced costs of avoiding mooring equipment installation might be attractive, there are a number of disadvantages to DP rigs. These include the cost to operate, which can be up to 150,000 litres of diesel per day, the inevitable environmental implications of this at a time when the oil & gas industry has to defend its environmental credentials, and the potential NOx and CO2 taxes. Some DP rigs have proved so expensive to transport that they end up being permanently moored.

With operators so sensitive to costs, the idea of rigs travelling the world without any mooring requirements might seem attractive. But a more realistic and practical solution would be to ensure that mooring equipment is readily available at a local level.

Stevtrack and Spin BuoyStevtrack and Spin Buoy undergoing offshore tests.

Local partnerships

Today’s mooring service providers need to develop local partnerships and hubs so that that a full portfolio of mooring equipment is available in key regions the world, negating the high shipping and transportation costs and making full use of local teams and their expertise.

Viking has established an extensive network of local partnerships around the world. For example, a partnership in Egypt has ensured that it has extensive storage space in Alexandria with the ability to ship equipment immediately to offshore exploration areas, such as the Gulf of Suez; in Malta, Viking has an extensive stock of mooring equipment, serving the central and western Mediterranean and the markets of Libya, Algeria and Tunisia; and it also has a base in Ghana, an ideal location for large- scale deployments in Angola, Nigeria and Ghana itself. Plans are also advancing to establish partnerships in Brazil and West Africa, and the company recently transported equipment worth US$50 million to both Australia and Singapore to ensure Viking is well positioned to react to the local employment demands of southeast Asia and Australasia. OE

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