Exploration and production operations in increasingly deep and difficult waters demand advanced technical expertise. Continuous technological progress has led to the development of large-scale platforms and production vessels, as well as high-performance drillships and robotic equipment that resembles a subsea factory.
At water depths of less than 200-300 meters, offshoreRefers to sea-based oil exploration and production operations, as in "offshore license" or "offshore drilling". platforms are fixed structures built on steel or concrete legs resting directly on the sea floor. They are connected to wellheads and pipelines via rigid tubes. Greater depths require the use of floating facilities that are kept in place by floats, tensioned cables or anchoring systems. They are connected to the wells using flexible risersIn offshore oil production, risers link the seabed to the surface and are primarily used to transfer oil....
Deepwater operations at water depths of more than 500 meters require major resources and sophisticated solutions. For a large field this can mean an investment worth billions of euros1.
Deep Offshore Drilling
A drillship is a massive vessel equipped with extra-long cables and heavy pipes that are used to drill wells at water depths of up to 3,000 meters. The wells themselves can exceed 7,000 meters. Drillships often feature two drillingThe process of boring a hole into the ground using special equipment... derricks to improve efficiency and output. This is important, as operating one of these specialized vessels can cost up to $1 million per day.
Another way to reduce costs is to limit the number of vertical wells by drilling long horizontal or high angle wells designed for optimal drainage.
4°C: the temperature of the sea below 600 meters
Instead of using platforms to pipe up oil from large reservoirs in areas where pipelinePipeline used to transport gas over a long distance, either on land or on the seabed. infrastructure is non-existent, producers use huge Floating Production Storage and OffloadingA self-contained floating vessel that can process crude oil and store until it is transferred (offloaded) to a tanker... vessels that are anchored to the seabed.
The largest FPSOs are more than 300-meters long and 60-meters wide. The hull has a storage capacity of two million barrels and the deck can accommodate production and processing facilities weighing thousands of tons, as well as the crew quarters. TankersVessel used to transport bulk liquids in huge tanks. The best-known tankers are oil tankers, which carry crude oil. can moor alongside the vessel and load directly at sea. Some producers are planning to build floating liquefied natural gas (FLNG)Intended for the development of offshore gas deposits, Floating Liquefied Natural Gas (FLNG) facilities are designed to... facilities that will enable them to liquefy natural gas immediately after production.
The vessels are connected to the seabed by an assembly of pipes, known as risers, that transfer well fluids to the surface. The conduits are several dozen centimeters in diameter and up to three kilometers in length.
The deepwater environment is cold, dark and subject to high pressure. At a water depth of 600 meters, the temperature drops to 4°C. At a depth of 1,500 meters, the pressure is 150 bar, equivalent to a force of six tons exerted on a surface area the size of a credit card.
A combination of low temperatures and high pressures can cause hydratesA hydrate is a compound formed by the addition of water to another molecule. Hydrates have a crystalline structure, which means that... or bits of ice to appear in the risers, thereby preventing the oil from flowing upward.To inhibit plug formation, various solutions have been developed, including insulation and heating systems and high-performance materials similar to those used for astronauts' spacesuits.
Deep offshore operations take place at water depths of more than 3,000 meters, and some wells go down 7,000 meters below the sea.
A Subsea Factory
A growing number of operations can be performed directly on the sea floor. Gas can be separated from the oil, for example, and compressed for long-distance shipping. Water too can be separated from the hydrocarbonsThe final phase in petroleum system formation, after a deposit has accumulated.... This is an important operation since the water cut increases as the oil field ages. Deepwater seabed treatment of water is also under study.
These techniques, combined with traditional monitoring and maintenance, involve the development and installation of hydraulic or electrically-operated robotic equipment. The resulting subsea factory is controlled by an FPSO.
Oil and Gas Extraction
FPSOs aren't suitable for extracting oil and gas from small, isolated fields often located several hundred kilometers from the coast. To extract oil, producers use electrically-heated pipes. In the case of gas, it's necessary to use chemical products called inhibitors to prevent hydrate formation since there are no heating or insulation systems able to deal effectively with the cold temperatures.