A workover riser is a riser that provides a conduit from the upper connection on the subsea tree to the surface, and which allows the passage of wireline tools into the wellbore. A workover riser is not run inside a drilling marine riser and therefore it shall be able to withstand the applied environmental forces, i.e. wind, waves and currents. A workover riser is typically used during installation/recovery of a subsea VXT, and during wellbore re-entries which require fullbore access but do not include retrieval of the tubing.
A workover riser typically consists of the following (see Figure A.33): the tree running tool; a wireline coiled-tubing BOP, capable of gripping, cutting and sealing coiled tubing and wire; an emergency-disconnect package capable of high-angle release; retainer valve(s) to retain the fluid contents of the riser during an emergency disconnect; a stress joint to absorb the higher riser bending stresses at the point of fixation to the LWRP; intermediate riser joints; lubricator valve(s) to isolate the riser during loading/unloading of long wireline toolstrings; a surface tree for pressure control of the wellbore and to provide a connection point for a surface wireline lubricator system; a means of tensioning the riser, so that it does not buckle under its own weight.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards
Jointed riser that provides a conduit from the subsea tree upper connection to the surface and allows for the passage of tools during workover operations of limited duration, and can be retrieved in severe environmental conditions. NOTE Historically, workover operations have normally been performed in open sea (i.e. for vertical tree systems), but can be performed inside a drilling riser, provided sufficient barrier elements are available.
Source: API Standard 2RD, Dynamic Risers for Floating Production Systems, Second Edition, September 2013. Global Standards
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards