By Jack Rosebro
|Wind and solar powers the North Sea Cutter platform.|
Royal Dutch Shell has begun pumping natural gas from its wind- and solar-powered Cutter micro-platform, sited on a marginal-production gas field underneath the southern North Sea.
The unmanned platform is supported by a monopost, which is based on offshore wind-turbine designs. Powered by a pair of small wind turbines and a pair of solar panels, the platform measures eight meters square. The use of renewable energy generation equipment not only provides green power, but reduces the cost of providing a subsea cable to power the platforms. The platform’s US$143 million fabrication cost alone is around 40% of that of traditional platforms.
The platform has three main elements. The foundation consists of a hollow pile 4.2 meters in diameter pushed into the seabed. The actual tower is placed on this pile, which projects from the seabed. To minimize the effects of hydrological forces as much as possible the diameter of the tower at sea level is a mere 2.5 metres. The actual platform is situated at a height of around 16 metres.
|The micro-platform design.|
The Monotower is also relatively light in comparison to traditional platform design (around 150 tonnes topsides and 250 tonnes substructure) and so can be installed with a drilling rig rather than a large crane barge. Shell has a controlling interest in the platform; the balance is owned by ExxonMobil.
Safety valves on the platform will be able to shut down production of the wells in case of emergency and the wells themselves are also equipped with subsurface emergency shutdown valves. The platforms carry equipment to inject corrosion and hydrate inhibitors into the wet gas pipeline as well as wind turbines and solar collectors for power, and the mandatory navigation lights.
The Monotower is not equipped with helidecks. Scheduled maintenance will be carried out once every two years with a jack-up rig while interim inspection visits will be made by boat, as is currently carried out on a few other Shell offshore platforms.
Production is projected to be in the range of 3 million cubic feet per day for the next 15 years. The reduced operating energy costs of such platforms help make the recovery of smaller pockets of oil and gas economically feasible.
Cutter is based in the southern sector of the North Sea, some 75 miles (120 km) from the Norfolk coast. It exports to the Bacton Gas Plant over the Shell-operated Carrack and Clipper platforms, a total distance of around 175 km in length to the UK Norfolk coast.
|Mars. Click to enlarge.|
Separately, on the mega-end of the offshore platform scale, Shell announced that it is ahead of schedule to restart production from its Mars Tension Leg Platform (TLP), damaged by Katrina. Mars is the largest producing platform in the Gulf of Mexico that was affected by Hurricane Katrina, representing about 5% of current Gulf of Mexico daily production.
Based on progress to date, Shell expects that construction activity necessary for initial production at Mars will be complete by the end of April. A brief re-commissioning and start-up process will follow, and partial production is expected to resume in the second half of May. Mars production is expected to be restored to pre-Katrina rates by the end of June.
Shell operates the Mars platform with a 71.5% working interest; BP has the remaining working interest.