As the ageing subsea well stock continues to grow, operators are seeking more efficient intervention solutions to maximise and extend existing production. Applications which require only the delivery of fluids to a reservoir or flowline such as acid stimulation, scale squeeze, and flushing may be accommodated for using an open-water hydraulic access (OWHA) system. When in-well access is not required, an open-water downline may be deployed from a vessel, connected to a subsea access point, and used to convey fluids. For deep water applications, the use of coiled tubing as an open-water downline has emerged as the preferred solution.
A method for riserless intervention of a subsea well includes connecting an intervention assembly to a bottom hole assembly (BHA). The BHA is connected to coiled tubing. The method further includes lowering the intervention assembly to a blowout preventer (BOP) fastened to a subsea production tree using an injector of a support vessel engaged with the coiled tubing fastening the intervention assembly to the BOP slacking the coiled tubing using the vessel injector engaging a stripper of the intervention assembly with the coiled tubing and driving the BHA through the tree and into a wellbore using a subsea injector of the intervention assembly while synchronizing both injectors to maintain the slack in the coiled tubing.