Watch: Shell's Monster Vessel for LNG Production
David Wagman | July 05, 2017
In an undated photo, the final topside module is lifted onto the Prelude FLNG vessel.
Royal Dutch Shell’s Prelude floating liquefied natural gas (FLNG) facility left the Samsung Heavy Industries shipyard in Geoje, South Korea, in late June and was being towed to North West Australia.
On arrival at the Prelude offshore gas field, 475 kilometres (295 miles) north-north east of Broome, Western Australia, pre-installed mooring chains will be lifted from the seabed and secured to the facility. Once secure, the hook-up and commissioning process will begin. Cash flow from the project is expected in 2018.
Shell says that floating LNG consolidates the traditional offshore to onshore LNG infrastructure into a single facility that is based over the fields.
The FLNG facility gathers, processes, stores, and offloads natural gas and condensate products at sea.
The Prelude FLNG facility is 488 meters long and 74 meters wide, making it one of the largest offshore floating facilities ever built. Its lifespan is expected to be 20-25 years.
A team of between 120-140 people will work on board Prelude during operations. The project will also be supported by teams and contractors across Perth, Darwin and the Kimberley in Australia.
The Prelude FLNG facility will be operated by Shell in joint venture with INPEX (17.5%), KOGAS (10%) and OPIC (5%).
FLNG removes the need for pipelines to shore, dredging, and onshore works. Shell says it is also a competitive solution for fields like Prelude, that are remote and hard to access.
The Prelude FLNG facility will be moored near to the Prelude field location in 250 meters of water, by four groups of mooring chains. Each mooring chain will be held to the sea floor by piles.
The facility has been designed to withstand severe weather, including up to a "10,000 year" storm, and will remain onsite during all conditions.
Seven production wells will feed gas and condensate from the reservoirs via four flexible risers into the facility. All subsea connections join the facility via the turret. The turret’s swivel design enables the facility to pivot according to wind and sea conditions while it remains fixed to the sea floor.
The Prelude FLNG facility has thrusters to ensure it remains steady during production and offloading, but it is a fixed facility, with no means of propulsion. The management of subsea wells and manifolds is carried out via umbilicals connected through the turret to the control room on the facility.
The processing of gas and condensate occurs in modules onboard that occupy an area approximately one quarter the size of a typical onshore LNG plant.
Shell’s Dual Mixed Refrigerant (DMR) process is used to liquefy the gas. Prelude’s LNG and LPG will be offloaded via a side by side vessel configuration using specially designed cryogenic loading arms. Ships will load condensate from the rear of the facility using a floating hose arrangement. The products will then be shipped directly to customers around the world.
