Subsea wireline systems
Subsea wireline systems involve the use of subsea pressure control equipment (including a lubricator), attached directly to the top of the subsea tree.
Typical subsea wireline systems use a surface-mounted wireline winch/reel on the intervention vessel.
Designs also exist for systems involving deployment of the winch at the subsea tree, thus decoupling the vertical movement of the wire from the vessel motion, however such systems have the corresponding features of some loss of “feel” for the wireline operator, as well as additional potential leakpaths and more complex subsea machinery.
A key design feature of subsea wireline systems is whether or not hydrocarbon fluids are returned to the intervention vessel during the operations. If hydrocarbons are/can potentially be returned to surface, then the classification requirements for the vessel are much more onerous than for a vessel using a system in which hydrocarbons are not/cannot be returned to the surface.
A typical subsea wireline system (i.e. using a surface-mounted wireline winch/reel) consists of the following major components: a tree connector; a lower lubricator assembly consisting of a wireline cutting valve and wireline BOPs, for pressure control
of the well in the event of an emergency disconnect; an upper lubricator assembly consisting of a connector, tool trap, lubricator sections, wireline BOPs, stuffing box (for slickline) and a grease injection system (for monoconductor line), for loading and unloading of wireline tools; a surface-mounted wireline winch/reel (fitted with a motion compensation system); a control system, similar to a WOCS as described in A.11.2.3, for controlling the subsea tree and downhole safety valves as well as all the valves and functions contained within the subsea wireline equipment; a handling system for deployment and retrieval of the subsea equipment (usually with guidewires); a supporting ROV spread for observation and operation manual overrides, etc., as required.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards