All offshore oil projects are designed with its final day in mind. Long before a floating production, storage and offloading (FPSO) vessel begins producing oil, operators must plan how wells will be sealed, subsea infrastructure managed, and facilities safely removed, reused or retired when production ends.
For ExxonMobil Guyana, decommissioning planning forms part of the lifecycle of each development in the Stabroek Block. The company’s preliminary plans exist because offshore infrastructure cannot simply be abandoned after a field stops producing. Instead the U.S. oil major must demonstrate how environmental risks will be managed and how waste generated during the process will be handled.
Exxon’s end-of-operations decommissioning plan covers Liza 1, Liza 2, Payara, Yellowtail, Uaru, Whiptail and the Hammerhead development in the Stabroek Block. Here’s how that process works.
What happens after the last barrel?
Offshore projects move through several stages, including exploration, construction, installation, production, maintenance and eventual closure.
For ExxonMobil’s projects, detailed decommissioning activities are expected to begin about three to five years before the end of a field’s life. It is expected that the operator submits an updated decommissioning plan to Guyanese regulators for approval. The plan must comply with Guyana’s environmental and petroleum laws, including the Environmental Protection Act and the Petroleum Activities Act, as well as applicable international standards.
What happens to wells, subsea equipment and FPSOs?
Once the plan is approved, the first step in closing an offshore field is permanently sealing wells to prevent hydrocarbons from escaping into the environment.
Hammerhead’s preliminary plan states that wells will be plugged and abandoned using barriers designed to contain reservoir fluids.
Subsea infrastructure, including risers, pipelines, umbilicals, flowlines and other equipment, will also be assessed before a final decision is made. Depending on the results of those assessments, some infrastructure may be removed, while other equipment could remain on the seabed if that option is considered safe and appropriate. The decision depends on factors including safety, environmental impact, technical requirements, social considerations and cost.
FPSOs however, follow a different process because they are floating facilities. Unlike infrastructure fixed to the seabed, these vessels can potentially be disconnected from their mooring systems and moved to another location for reuse or decommissioning.
Managing environmental and safety responsibilities
Decommissioning is not only an engineering activity. It also requires environmental management, waste handling and monitoring throughout the closure process.
Waste generated during decommissioning may include hazardous and non-hazardous materials, which must be handled according to Guyanese regulations, international conventions and industry practices. Management options may include recycling, treatment, approved disposal methods or transportation to licensed facilities onshore.
Decommissioning plans also include measures such as marine safety zones, waste tracking, emissions monitoring and requirements for contractors and workers to follow health, safety and environmental procedures.
How Guyana applies its environmental stewardship to offshore oil risk management | OilNOW
Who pays for decommissioning?
Although Guyana’s offshore projects are expected to produce for decades, discussions have already begun about who will pay when those developments eventually reach the end of their lives.
In October 2024, ExxonMobil Guyana President Alistair Routledge said the company would work with the Guyana government to establish an independent decommissioning fund, which would ensure money is available when offshore facilities eventually need to be retired.
