Introduction — Offshore operations involve exploring for and producing oil or gas at sea. They use drillships, fixed or floating platforms, subsea wells and specialized transport systems. Projects can access substantial resources, but require high investment, rigorous risk management and planning covering facilities’ entire lives through decommissioning.
Key facts
- Offshore: oil or gas activity at sea, unlike land-based onshore operations.
- Equipment: fixed or floating platforms, subsea wells, pipelines and specialized vessels.
- FPSO: a floating unit producing, processing and storing hydrocarbons before transfer to a tanker.
- Central challenge: well safety and preventing releases into the marine environment.
What does offshore mean?
Offshore refers to activities away from land, in coastal waters or the open sea. It covers prospecting, drilling, production and oil and gas transport. Operations vary with depth, distance from shore, seabed geology and existing infrastructure.
Shallow-water projects can use seabed-supported platforms. In deeper waters, floating units or subsea systems connected to processing facilities may be preferred. Choices depend on deposit size, expected production duration, weather and ocean conditions, and pipeline costs to shore.
How does offshore drilling work?
Exploration campaigns begin with geological and seismic studies. When a prospect appears promising, a drilling vessel or platform drills an exploration well. In deep water, the well crosses the water column and enters rock layers beneath the seabed. Riser conduits and specialized equipment connect the well to the drillship.
Pressure control is fundamental. Teams adjust drilling fluids and install mechanical barriers to prevent uncontrolled reservoir fluid flow. A blowout preventer, or BOP, combines safety valves designed to close the well if control is lost. Equipment must be appropriate, tested, inspected and operated by trained teams.
If a discovery is confirmed, appraisal wells clarify reservoir characteristics and extent. Production wells can subsequently be drilled from a platform, floating unit or seabed. Several wells can be grouped and connected to a shared processing center.
Platforms, subsea systems and FPSOs
Fixed platforms rest on structures anchored to the seabed. They accommodate drilling or processing equipment and personnel work and living areas. They are mainly suitable where depth and seabed conditions permit permanent structures.
Floating production units maintain position through moorings or dynamic systems. Floating production, storage and offloading units, or FPSOs, receive extracted hydrocarbons, separate them and process them. Oil can be stored onboard and periodically transferred to tankers. Gas can be compressed, reinjected into the reservoir, transported by pipeline or processed for liquefaction according to project configuration.
Subsea systems comprise wellheads, manifolds, flexible pipelines and control equipment installed on the seabed. They can connect to a platform or FPSO, allowing remote areas to be developed without a surface structure above every well. Maintenance and intervention sometimes require remotely operated vehicles and specialized vessels.
Main stages of an offshore project
Projects progress through exploration rights, data acquisition, drilling, discovery appraisal and an investment decision. Once development is approved, operators build and install equipment, drill production wells and establish crude or gas export infrastructure.
During production, teams monitor pressure, corrosion, flows, safety systems and well integrity. They also manage produced water, emissions, waste and associated gas. At the end of field life, wells must be plugged and facilities removed or handled according to regulation and the approved plan.
Timelines and costs are generally higher than for onshore projects. Equipment must withstand pressure, corrosion and marine conditions. Vessels, spare parts and specialist teams must be available despite bad weather or remoteness. Delays can affect supply contracts and expected revenues.
Risks, safety and the environment
Offshore operations pose risks to personnel, vessels, facilities and marine environments. Losing well control can cause a blowout, fire or spill. Safety plans rely on multiple barriers: well design, pressure monitoring, preventers, emergency drills, containment equipment and offshore response capabilities.
Leak prevention covers the entire chain, from drilling to pipelines and loading operations. Impact studies must consider marine habitats, fishing, underwater noise, releases and cumulative effects alongside other activities. Monitoring after facility closure is also necessary to detect possible leaks or failures.
Offshore operations and African prospects
Several basins offshore West, Central and Southern Africa host oil and gas projects. Developments in Senegal and Mauritania, including the Grand Tortue Ahmeyim gas field, illustrate cross-border cooperation around offshore infrastructure and LNG exports. In Côte d’Ivoire, Baleine field development highlights deepwater discoveries’ potential and local content challenges.
For host states, offshore projects can generate revenues, specialist jobs, service contracts and infrastructure. Benefits nevertheless depend on contractual arrangements, taxation, local company participation, available skills and operational oversight capabilities. Transparent costs, volumes and payments are essential to assessing value created.
Frequently asked questions
What is the difference between offshore and onshore?
Offshore means operations at sea; onshore means land-based activities. Equipment, costs, logistics resources and risks differ by environment.
What is an FPSO?
It is a floating unit receiving and processing produced hydrocarbons, then storing oil before transfer to a vessel. It can also serve as a production center for connected subsea wells.
Does offshore necessarily mean deep water?
No. Offshore operations can take place near the coast in shallow water or in very deep areas. Depth partly determines technology, costs and project organization.