Abstract
The use of the tethered BOP at Petrobras intends to enable the operation of Dynamically Positioned Rigs in shallow waters, allowing drilling or workover in wells in congested areas or subject to environmental restrictions due to corals or marine fauna. The BOP tethering technology also allows the use of newer generation rigs, whose BOPs are larger and heavier, in old wells not designed for such loads. ROV and surface images of the critical moments for the BOP tethering show the lessons learned in this operation, such as schematics and drawings of improvements implemented or suggested for future opportunities. During the operations, many opportunities for improvement were identified, such as: the ideal drilling schedule to launch the anchors with the Anchor Handling Tug Supply Vessel (AHTS); the imprisonment of the cables by the cement of the surface casing in the mud line; the knots that occurred in the cable after replacing the tensioner system; the feasibility to use the rig drill string instead of an RSV to replace the tensioner; and the need of unlatching the BOP to replace the tensioner system, with suggestions to avoid this in the future. The challenges overcome in this operation allowed the development of new solutions and procedures for tethering the BOP, dispensing with the use of a RSV, and improving the contractor's initial procedure. The success of this system enables rig operations in several locations that are currently unfeasible, whether for plug & abandonment of old wells or for drilling new locations in shallow water. The first use of tethered BOP in association with real-time Riser Analysis in Brazil resulted in the reduction of the risk associated with an emergency disconnection, providing a larger operational window and a more accurate analysis of well structure fatigue.
