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Barryroe oilfield, Ireland

To screen and select concept options for development of Ireland’s first major offshore oilfield, we used an innovative matrix approach that strengthened commercial and technical viability.

Our approach resulted in a transparent and totally traceable full field concept selection that matches our clients’ technical, safety, environmental and commercial objectives.

40x10km
size of oilfield
100m
depth of water
50km
distance from mainland
100,000
barrels per day forecast oil capacity
25
years design life

The challenge

Our client Providence Resources and Lansdowne Oil & Gas tasked us to:

  • Identify, evaluate and screen options for offshore oil and gas production facilities, including drilling and oil and gas transport

  • Assess a range of fixed, floating and hybrid systems to define a preferred concept.

  • Fully demonstrate all reasoning.

Key considerations

Oil properties High wax content and pour point temperature mean that heating, insulation and chemical strategies may need to be applied to assure flow.

Production The use of dry ‘trees’ and wellheads – which control well activities – is preferred. They must therefore be located above the water rather than on the seabed.

Environment Located in the Celtic Sea, conditions are challenging because of high wave loads and water swells, similar to North Sea locations.

Qualitative screening

Our multidisciplinary evaluation first measured options against our clients’ key criteria using a definitive, bespoke ‘mind map’.

Incompatibility with dry trees eliminated semi-submersible platforms, WHPs, subsea wells and tie backs and subsea process facilities. FPSOs and compliant towers were not suited to the conditions, unmanned production buoys couldn’t support flow assurance facilities and octabuoys are not yet in use.

Quantitative screening

Next, we ranked the remaining options in a matrix by assigning values to our clients’ selection priorities and ‘scoring’ each facility.

In this way, we discounted GBS and TLP options on cost grounds, as well as highlighting the environmental drawbacks of the GBS option. Hybrid facilities, such as WHP and jack up or FPSO combinations, also proved too costly, as did MOPUs. This mechanism gave our clients a clear system to easily assess viability.

Fixed platform

Our final concept includes three PUQ (process, utilities, quarters) platforms, anchored directly to the seabed with steel supports, and jack-up rigs – mobile, self-elevating drilling platforms.

This flexible option provides robust and proven technology suited to the long life of the field, manageable safety considerations and lowest combined capital, drilling and operating costs. Export of oil and gas could be via subsea pipeline to shore, though floating storage units and shuttle tankers are viable too.

The result

A transparent and totally traceable full field concept selection that matches our clients’ technical, safety, environmental and commercial objectives. The field embraces extended reach drilling, which allows a single platform to exploit a much greater reservoir area.

The two-stage method, which included a bespoke ‘mind map’ and an innovative matrix approach, was undertaken by our offshore design specialist Procyon Oil & Gas, which joined Mott MacDonald in 2012.

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