Abstract: An apparatus for performing operations on an offshore well includes a subsea wellhead assembly. A riser extends from the subsea wellhead assembly to a surface vessel. A tool connects to a running string and is lowered through the riser into the wellhead assembly for performing operations at the wellhead assembly. A subsea controller is located adjacent the subsea wellhead assembly. The subsea controller controls the operation of the tool. A surface controller is positioned on the surface vessel, and is in communication with the subsea controller via a control line extending downward from the surface controller to the subsea controller. The control line extends downward from the surface controller along an exterior of the riser.

Abstract: A method performing an operation in a subsea wellhead assembly through a riser extending between the wellhead assembly and a surface platform includes the step of connecting a surface blowout preventer to an upper portion of the riser. Then a tool is connected to a string of conduit. A control line is then connected to the tool, extended alongside the conduit. The tool and control line are lowered through the blowout preventer and riser. The method also includes the step of mounting a slick joint to an upper end of the conduit when the tool is near the wellhead assembly. The control line is then linked through the slick joint and extends to the surface platform. The method also includes the step of communicating with the tool via the control line and performing an operation in the wellhead assembly with the tool.