Statoil is operating several fields where downhole continuous injection of scale inhibitor is applied. The objective is to protect the upper tubing and safety valve from (Ba/Sr)SO4 or CaCO3 scale, in cases where scale squeezing may be difficult and costly to perform on a regular basis, e.g. tie-in of subsea fields.
Continuous injection of scale inhibitor downhole is a technically appropriate solution to protect the upper tubing and safety valve in wells that have scaling potential above the production packer; especially in wells that do not need to be squeezed on a regular basis due to scaling potential in the near wellbore area.
Designing, operating and maintaining the chemical injection lines demand extra focus on material selection, chemical qualification and monitoring. Pressure, temperature, flow-regimes and geometry of the system may introduce challenges to safe operation. Challenges have been identified in several kilometers' long injection lines from the production facility to the subsea template and in the injection valves down in the wells.
Field experiences showing the complexity of downhole continuous injection systems regarding precipitation and corrosion issues are discussed. Laboratory studies and application of new methods for chemical qualification are presented. The needs for multidisciplinary actions are addressed.