Buoyant Turret Mooring Developed for typhoon or iceberg prone areas where a rapid disconnection/ reconnection is required. The disconnectable part of the turret is a submerged buoy which supports the crude oil and gas risers and the mooring legs. In the operating mode, the mooring buoy is connected to the turret by a structural connector. The turret structure is located in the forepeak of the tanker and supported on a weathervaning bearing. The turret extends up through the tanker with the reconnection winch, flowline and control manifolds and fluid swivels located above the main deck. The disconnection and subsequent reconnection is carried out from the tanker without external intervention.
Catenary Anchor Leg Mooring A floating structure that performs the dual function of keeping a tanker moored on a single point and transferring fluids (generally oil, gas or by-products) while allowing the ship to weathervane. It consists of a circular floating buoy anchored to the seabed by means of four, six or eight chain legs draped radially in a catenary curve. The bottom ends of the chains are fixed to the seabed by either conventional anchor legs or piles. The buoy itself is free to move up and down, sideways and in pitching and rolling motions. The tanker is moored by hawsers to a turntable attached through heavy-duty roller bearings to the top of the buoy. This turntable is free to rotate through 360 degrees and is fitted with piping, valves, mooring equipment, floating hose connections, navigation aids and, in most cases, lifting facilities to support maintenance activities.
Liquids condensed from a gas stream, made up of a range of heavier hydrocarbons. For gas fields, condensate typically refers to the hydrocarbon liquid separated from the well stream fluid, which can be stabilised, stored and exported as a high value liquid product.
A ship-shape vessel with one crane or semi-submersible vessel with one or two cranes for lifting platform modules and structures at sea. The crane hoisting capacities are substantial and range from 300 tons to 8000 tons. Cranes allow for moving the hook-load vertically and horizontally (in a 360 degree radius). Nowadays also frequently used to install heavy equipment on the seabed. In medium water depths the crane vessel is anchor-moored. In deepwater areas the vessel is dynamically positioned.
Low temperature processing, generally sub zero. For LNG this can be as low as minus 162 degrees centigrade.
Dry Completion Unit A floating facility carrying surface completed wells, i.e. the xmas trees are located above the surface of the sea, on the floater, as opposed to the seabed. The rigid pipes (tubing, casing etc.) that link the trees to the wells require high tension to avoid buckling. A key feature of a DCU is therefore the need for constant tension to compensate for the floating heave motion. Generally, a DCU also carries basic drilling equipment to allow down-hole intervention on a tender assist mode. It can also feature a full drilling capability.
More than 300 metres water depth.
The removal of sulphate ions from seawater prior to use as injection water. This operation is required when the formation contains barium and strontium and to a lesser extent calcium to prevent re-agitation of sulphates which will cause plugging of the flow-path of the produced fluids from the reservoir.
Dynamic positioning A station keeping system for floating units which uses thrusters to compensate wind, wave and current forces in a dynamic controlled mode to keep the unit on a predetermined location and heading at sea.
A ship-shape vessel for drilling and completing wells in medium to deepwater applications. The drilling equipment onboard of the ship enables drilling the well, running the protective casing in the well (preventing collapse of the drilled hole), and installation of the subsea xmas tree. In medium water depths the drill ship is anchor-moored. In deepwater areas the ship is dynamically positioned.
Dry production trees
See Surface (xmas) trees.
Diving Support Vessel A dedicated vessel, most frequently d.p., for assistance of subsea diving and installation work.
Dry Tree Unit A motion stabilized floating vessel that supports vertical steel risers from sea floor well-heads providing well access for drilling or work-over operation.
Dead weight , The total weight of cargo, fuel, fresh water, stores and crew that a ship can carry when immersed to her load line.