Subsea engineering and construction involves the building and maintenance of underwater equipment and pipelines.
Survey ships with specialist technology are used to image, map and examine seabed conditions in advance of drilling wells or installing pipelines. Their work influences decisions over where equipment should be installed and the route of pipelines.
Excavation and trenching
Pipelines and umbilicals are buried below the seabed by digging down before being covered. This is carried out to protect them from damage by currents or items such as fishing nets or anchors.
Crude oil varies in its temperature and thickness (viscosity). It also contains many different chemicals which can hamper its flow through a pipeline. Flow assurance examines how different oil behaves as it moves through a pipeline to help improve the flow.
Separation and processing
Equipment is used to separate oil, gas and water beneath the water surface. Each substance can then be processed individually back on the surface.
Inspections are use to determine the need for maintenance work on underwater equipment. This is normally carried out using divers, ROVs and AUVs, often with specialised electronic equipment to take detailed images or readings.
Equipment can suffer corrosion as a result of being in the sea and from being exposed to chemicals. Equipment is checked by divers, ROVs and intelligent pigging to assess how it is being affected. Corrosion can weaken equipment which may result in leakages or structural failure.
Subsea control systems
Control systems involve the manipulation and monitoring of all underwater equipment such as christmas trees, manifolds and valves. A surface master computer is connected with via umbilicals to underwater control pods on subsea equipment. This allows the operator to monitor and operate equipment to maintain safe production.
The subsea industry uses a variety of equipment to extract oil and gas form beneath the seabed including pipelines and offshore drilling machinery.
Remotely Operated Vehicles (ROVs) are used to access difficult to reach locations in the sea. The unmanned vehicles are connected to the surface by umbilicals and controlled by technicians using a joystick a bit like playing on a PlayStation. ROVs carry out tasks such as video monitoring, inspection, repairs and construction.
Autonomous Underwater Vehicles (AUVs) are similar to ROVs but they can be pre-programmed and piloted by an onboard computer. Once put into the water, AUVs can be left to carry out their tasks unsupervised before returning to base (the surface).
This vital piece of subsea equipment is placed above the well on the seabed to control the flow of oil or gas. Once opened the flow passes through a line to the ship or platform at the surface. Trees can provide additional functions including chemical injection into the well and intervention.
Forcing a pig (a device with blades or brushes) through a pipeline for the purposes of moving or separating fluids, cleaning or inspection is called ‘pigging’. Inspection pigs are sometimes called intelligent pigs and can be used to check for corrosion and the wall thickness of the pipeline to help identify potential leaks.
Dynamic positioning, deepwater positioning
Onboard computers use satellite signals to keep a vessel in a stationary position over a subsea oil well or construction site using thrusters or propellers on the vessel.
A tube or pipe carrying oil, gas or water to the surface. The riser is flexible to allow it to move with the motion of the sea without breaking.