Rigid workover risers
The most conventional LWI system involves the use of a standard rigid workover riser system (as described in A.11.2), deployed from either a semi-submersible/monohull vessel, e.g. a dive-support vessel or light well construction vessel.
A rigid workover riser system allows conventional wireline and coiled/reeled tubing techniques to be used for downhole intervention/service work. Workover riser systems designed for intervention on wells fitted with subsea HXTs require the use of large-bore components [e.g. a 476 mm (18 3/4 in) tree connector, large-bore valves and a large-bore riser] in order to interface with the top of the HXT and to be able to retrieve the largebore plug installed in the TH and possibly in the internal tree cap.
While this system provides maximum operational flexibility in terms of the work that can be performed downhole, it also has the greatest requirements in terms of vessel size, stationkeeping ability, deck space, variable deckload, riser system handling equipment, etc.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards