How FPSO and FLNG Projects Move from Discovery to Construction
A practical guide to the path from discovery and appraisal through concept select, pre-FEED, FEED, FID, EPC and start-up.
FPSO and FLNG projects often seem to appear overnight. A final investment decision is announced, contractors are named, and hull and topsides work soon follows. Inside the operator's organization, however, years of work have already taken place. After a discovery, the team must appraise the resource, compare development concepts, carry out pre-FEED and FEED, negotiate commercial terms, secure permits and financing, pass internal reviews and finally reach FID. Five to ten years from discovery to FID is not unusual for a large deepwater development, and some take longer.
The floating solution is not chosen from scratch during FEED. The oil and gas mix, distance from shore, existing infrastructure, route to market, development scale and host-country requirements all influence the decision much earlier. By the time FEED begins, the main development concept has usually been selected. The work then shifts to defining the design, improving the cost estimate and settling the project's risks and contractual boundaries.
1. A Discovery Must First Be Appraised
A successful exploration well only proves that a hydrocarbon accumulation exists. It does not mean development will begin immediately. Appraisal wells, seismic data and well tests are used to judge reservoir continuity, recoverable volumes, well productivity and the likely production profile. Many discoveries are never developed because their scale, cost or risk does not support a commercial project.
Fluid properties shape the engineering from the outset. Gas-oil ratio, pressure and temperature set the broad size of the processing system. Carbon dioxide, hydrogen sulfide and mercury can add material, equipment and safety requirements. Distance from shore, water depth, metocean conditions, permitting, local-content rules and regional security also enter the assessment. The operator is deciding whether the resource justifies more time and money.
2. FPSO and FLNG Are Not Default Choices
Once appraisal is far enough along, the operator moves into concept select. An oil-dominant deepwater project may compare an FPSO with a fixed platform and pipeline or a subsea tieback. A gas-dominant development may compare FLNG with an offshore pipeline to an onshore LNG plant, a regional pipeline or supply to the domestic market. A gas discovery does not automatically lead to FLNG, just as an oil discovery does not always require an FPSO.
An FPSO separates and treats the wellstream, stabilizes the crude, stores it and offloads it. Associated gas may be used for power, reinjected or exported. The facilities are complex, but their interfaces are well understood and the work can be divided into a number of systems and packages.
An FLNG facility must also pretreat the gas, liquefy it, store it at cryogenic temperature and transfer LNG to carriers. A change in feed-gas composition can alter the pretreatment and liquefaction design. Liquefaction duty then affects power generation, refrigeration, equipment layout and hull size. These systems are more tightly linked. FLNG is often considered for remote resources without suitable pipeline or onshore infrastructure, or where direct LNG exports make commercial sense, but it still has to compete with shore-based alternatives on cost, market access and execution risk.
The aim at this point is to choose the development route, not the final contractor. Once that route has been selected, the engineering team has a firm basis for the next phase.
3. Pre-FEED Gives the Concept an Engineering Shape
Pre-FEED turns the selected concept into an engineering scheme that can be tested and compared. The operator and its engineering contractors define which systems sit offshore and which are handled by another facility or onshore. They prepare early process diagrams, size the main systems, estimate topsides weight and footprint, test the layout and study storage, mooring and export arrangements.
For an FPSO, this work sets preliminary capacities for oil treatment, water injection and associated-gas compression or reinjection, along with the expected offloading frequency. For FLNG, it establishes feed-gas capacity, pretreatment boundaries, liquefaction capacity, storage volume and the proposed LNG carrier interface. The project is more than a concept drawing by this point, but many values are still moving. Cost remains a range estimate, and uncertainty of around 30% or more is common depending on how much engineering has been completed.
4. FEED Defines a Project for Investment and Tendering
FEED develops the project far enough to support investment approval, contract tenders and financing review. The process scheme, major equipment, redundancy philosophy, overall layout and key interfaces are defined in greater detail. Responsibilities between the hull, topsides, mooring, export system and subsea production system also have to be clear. The operator uses this work to update the capital estimate, choose a contracting strategy and prepare the FID submission.
For an FPSO, FEED checks whether oil-processing capacity matches the production and water-cut profile. It defines how associated gas will be exported, reinjected or used for power, and sizes the compression and water-injection systems. The mooring or turret arrangement is tested against availability, maintenance and safety requirements, while the need for equipment redundancy and online maintenance is reviewed.
FLNG FEED concentrates on the continuous chain from gas pretreatment through liquefaction to cryogenic storage and offloading. Changes to carbon dioxide removal, dehydration or mercury removal can affect the liquefaction plant. Liquefaction technology and energy demand influence equipment size, power generation and operating stability. Storage tanks, boil-off gas management and LNG transfer must meet both cryogenic and offshore safety requirements. A change to one major condition can quickly affect several other systems.
5. FEED Is Followed by Internal Review
As FEED nears completion, the operator subjects the project to a concentrated series of reviews. Engineering assurance teams challenge design assumptions, interfaces, redundancy and integrity. Economists rerun the effect of oil or gas prices, delays and cost overruns on internal rate of return and net present value. HSSE and ESG reviews cover permits, emissions, venting or flaring and the consequences of major accidents.
The contract model, financing plan and allocation of risk among project partners also need to be largely settled. The operator compares EPC, EPCIC, lease-and-operate and other structures, while confirming local-content obligations, government approvals, oil or LNG sales arrangements and sources of capital. The board or investment committee then decides whether the company is prepared to take the investment risk.
Many projects stop here for reasons other than technical feasibility. Cost, returns, contract terms, permitting or financing may fail to line up at the same time. A project can be put on hold and return years later under different market or resource conditions.
6. FID Is a Commitment, Not the First Day of Construction
At FID, the project partners formally approve the full investment, authorize the main capital commitment and allow the core EPC, lease or other project contracts to take full effect. For a large FPSO or FLNG development, this can mean approving several billion dollars of spending and locking in the main technical and commercial structure.
FID does not mean that a yard cuts first steel on the same day. To protect the schedule, an operator may sign conditional contracts, issue a limited notice to proceed or order long-lead equipment beforehand. FID matters because the project moves from a preparatory phase in which it can still be delayed or reshaped into full execution.
Fewer FLNG concepts reach FID than FPSO projects. FLNG usually carries a larger capital commitment and a more tightly integrated process plant. The developer must also align long-term gas supply, LNG sales, liquefaction technology, shipping arrangements and financing. If one part remains unresolved, the investment decision can slip.
7. Execution Begins After FID
After FID, the project moves through detailed engineering, procurement, hull and module fabrication, integration, offshore installation, commissioning and start-up. An FLNG project also requires extensive testing across the liquefaction modules, cryogenic storage and LNG transfer systems. Interface problems left in the design tend to surface during procurement, construction and commissioning.
The time from FID to first production varies widely. A conversion or redeployment can be quicker, while a large newbuild FPSO or FLNG facility still takes several years. News coverage often begins at FID or EPC award, but the project itself has already been active for years. For the operator, the nature of the work has simply changed: studies and approvals give way to engineering, procurement, construction and commissioning.