Through-flowline system intervention
TFL servicing can be used in subsea wells to perform various well-servicing operations, including: setting and retrieving flow control devices such as plugs (downhole and wellhead), static chokes, gaslift valves and inserting subsurface safety valves; gathering bottomhole pressure and temperature information via the use of temporary downhole gauges; acidizing, bailing, drifting, fishing, perforating, sandwashing, wax cutting, well killing, etc.
TFL servicing involves shutting in the target well and then pumping the required tools through a flowline/service line from the host facility to the subsea completion and thence downhole. Once the tools are pumped into position, the required functions are actuated by means of application of differential pressure to shear a pin, shift a sleeve, etc. Upon completion of the required task the TFL toolstring is pumped back to the host facility through the flowline/service line.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards