Going deep and getting heavy

Fred Tholen

December 1, 2014

The global fleets are growing – not least in order to cater for new deep water challenges. Fred Tholen takes a look.

Subsea 7’s new heavy construction vessel, under construction in South Korea, is set to make a splash when it joins the company’s fleet in 2016. The 160m-long, 32m-wide, vessel includes a new-design, 900-tonne, Huisman rope-luffing, knuckle-boom crane.  Photo from Subsea 7.

The pressure to innovate within the oil and gas sector is intensifying. Exploration and production from deep and ultra-deep water regions are set to increase compared with conventional production plays on the continental shelf. While operators need to maximize volume to make their operations profitable and sustainable, not all oil and gas is viable in shallow water. Meeting future energy demands from offshore oil and gas will depend on those operators who are increasingly looking to extract from reservoirs in deeper waters.

This trend is supported by Douglas Westwood, a research and consulting company, that identified an increase of 67% in deepwater production during the last decade, and is forecasting a further growth of 37% in 2020, which indicates a strong growth prospect.

Water depths are increasing and average tree water depth is now around 800m with indications that this could increase to around 1400m by 2020. In Brazilian waters, operators are reaching vast depths of 3000m and the question for industry is where the technical and commercial limits can be taken next.

So where are these contributing factors likely to have most impact? The geological-plays include areas such as Americas, Brazil, Africa and Asia Pacific and in regions such as Malaysia, Indonesia and India. Mexico is another hotly pursued area after recent changes in legislation now present a serious game play for international companies to set up operations off the coast of Mexico, and where a large part of the challenge is around deepwater drilling.

The challenges of operating in deepwater will inevitably have an impact on designs and requirements of the vessels needed for operating in these regions. Deepwater operations are normally further offshore and require larger and more complex units with increased endurance. There are also different facets of the operations that affect vessel design.

The challenges around deepwater are recognized as driving the design for larger multipurpose support vessels for remotely operated vehicle operations, which are inevitably needed replace traditional diving operations.

Also, with increased water pressure, subsea modules become larger and heavier which require more complex load handling equipment. This increases the size of the vessels used in deepwater operations. In the future, construction vessels with larger crane capacity to support this subsea work will be needed, and the increasing crane lifting capacity will drive the manufacture in larger sized vessels.

Larger load-handling equipment requires more complex structural interfaces with the vessel and can affect the vessel’s stability offshore, particularly in adverse conditions – a critical driver of vessel design.

Construction vessels with crane capacity of 250-tonne are fast entering the market and larger vessels with even larger crane capacity, up to 900-tonne, are being designed and built.

Photo from Royal IHC.
 

Consider also the water depth, which in itself can be challenging for vessel designers. For a subsea crane that is utilizing steel wire rope, the lifting capacity at 3000m water depth is reduced to approximately 50% compared to at sea-level. In other words it is not just the weight of subsea modules that dictates the crane capacity but importantly the water depth. In this area, innovative solutions such as module handling towers and artificial bounce assessments can be introduced.

Pipe laying vessels with deepwater capabilities are able to operate to depths of 2500-3000m, with large pipe storage capacity under construction to meet the increasing industry demand in deep and ultra-deep water operations.

The trends for vessels operating further offshore are generating new design specifications for greater carrying capacity, such as larger deck areas and storage capacity below deck with flexible tank configuration.

Likewise, regulations need to complement the changes and complexities of industry demand which, for example, require larger amounts of chemicals to be transported for supply, well testing and intervention.

Larger quantities of hazardous noxious liquids substances in bulk than the current 800cu m that today is the limit, stipulated in A.673(16), is in debate. The International Marine Organization is tackling this issue head on with a dedicated chemical code for offshore support vessels. When launched, this code will allow for larger quantities to be managed coupled with requirements for increased and robust contingencies around damage limitation and other safety related aspects inspired by the IBC (Dangerous Chemicals in Bulk) code.

With all the technical challenges and different statutory regulations imposed on vessels because of variances in operational challenges and different features, class needs to fulfil an important collaborative role in supporting the operator and industry stakeholders to ensure a sustainable supply chain.

The latest vessel designs responding to a more complex industry include:

Sapura Diamante: Pipe laying vessel (above)


 

Fredrik Tholen is Principal Specialist – Global OSV Market Manager. He graduated from the Technical University of Denmark with an as BSc in Naval Architecture in 1989, and started his career with design and construction of submarines at the Swedish Shipyard Kockums, and then later moved on to join Lloyds Register Group.

Tholen has been with Lloyds Register for more than 20 years, working with design support aspects with designers, shipyards and owners in different positions and locations, and recently managing Copenhagen’s Technical Support Office.