ExxonMobil Guyana’s proposed gas-and-condensate developments will rely on floating production, storage and offloading (FPSO) vessels configured differently from the vessels primarily producing crude oil offshore the country today.
Before gas and condensate can begin flowing through one of these facilities, its power, safety, utility and processing systems must be brought online through a carefully sequenced startup.
The proposed Longtail project, which is awaiting regulatory approval in Guyana, provides a look through its environmental impact assessment (EIA) at how that process is expected to unfold.
First, make the FPSO ready
The process begins with the basics. The Fire and Gas System and Integrated Control and Safety System must be fully commissioned and in service. Firefighting equipment must be available, and personnel must be trained to operate the safety and process systems.
How FPSOs in Guyana’s waters work and why they matter | OilNOW
Power generation, instrument air, nitrogen, heating and cooling systems, chemical injection, the flare system, drains, cargo systems, inert gas and seawater treatment must also be brought online.
A laboratory must be ready to analyze incoming fluids.
Preparing to receive hydrocarbons
The condensate (a light liquid hydrocarbon found in natural gas deposits) processing train is then prepared to receive fluids from the wells.
Vessels are filled with water to their normal operating levels and oxygen is removed using nitrogen. This allows fluids to be transferred safely through the separation stages.
The flare system is also purged with nitrogen, while process vessels and compression trains are pressure-cycled and continuously purged.
ExxonMobil’s H1 Stabroek drilling focuses on appraisal, gas, new oil target | OilNOW
Testing what connects the vessel to the wells
Before production begins, the risers, flowlines and umbilicals must be leak-tested.
The subsea oil flowlines and risers are then flushed with marine gas oil (MGO). The operation displaces fluids used during testing and prepares the subsea system for hydrocarbons.
The EIA states that the FPSO topsides will be considered “Live” during this stage. A safety stand-down will be held before the operation begins so personnel understand the work about to take place.
The gas injection system must also be prepared by clearing water from the risers and pipelines that will eventually carry gas. Nitrogen is used during this process to help displace the liquids and prepare the system for operation.
Then comes the first well
Only after the risers have been flushed and their condition confirmed by ExxonMobil can the first well be brought online.
Methanol will be injected during startup to prevent hydrates—ice-like deposits that can block flowlines and equipment—from forming as fluids from the well enter the FPSO.
The well fluids will initially pass through a test manifold and test separator before moving through the crude processing equipment. During the first well’s cleanup, some equipment may be bypassed to reduce the risk of blockages.
Bringing the gas systems online
Once production from the wells becomes stable, the FPSO can gradually bring its gas-processing systems into service.
Gas produced during the early stages of startup can temporarily be used for power generation. As the gas treatment system comes online, treated gas becomes available and the equipment needed to compress gas for injection can be started.
Other compressors are brought online in stages as a stable supply of gas becomes available from the separation process. The vapor recovery system, which captures gas vapors from the FPSO’s cargo tanks, can also begin operating once sufficient gas is available.
Eventually, once the facility is operating steadily and handling non-associated gas, the closed flare system is brought into service. Together, these steps progressively move the FPSO from initial production to normal gas processing and management.
