Traditionally, semi-submersibles have been used to perform interventions on subsea wells using a riser based system. However this method can be time consuming, expensive and requiring long lead times for both rig and riser system. Almost two decades ago a true breakthrough came with the courage to run e-line through open water to intervene in a subsea well, also referred to as Riserless Light Well Intervention – RLWI.
Capitalizing on existing, more readily available equipment to accomplish interventions, RLWI can be accomplished with purpose built vessels or a vessel of opportunity. No rig nor riser is required.
By far most interventions can be performed by wireline with applications covering from conventional e-line conveyed logging, perforation etc. to mechanical manipulation, obstruction removal to spotting chemicals or other fluids. Riser conveyed intervention is only required for complete workover where tubing is retrieved and/or where the application is to pump major amounts of fluid.