Inner Wear Liner for Top Tensioned Riser Sidetrack Drilling Operations

To increase well productivity, sidetrack drilling operations can be conducted through existing production top-tensioned risers (TTRs). Since 2014, Eni Petroleum have successfully conducted plug back, sidetrack, and recompletion of three wells at the Devil's Tower spar platform in offshore Gulf of Mexico. The platform has eight TTRs with subsea wellheads, which were subsequently tied back to the spar and completed in surface wellheads with dry trees. This paper presents the riser system design, challenges and the results from the pre-drill dynamic riser analysis and post-drill riser monitoring assessment due to environmental, vessel, and operational loads. This paper also addresses the key benefits and challenges involving the use of a temporary wear liner through the existing spar top tensioned riser system while working within the available aircan tension capacity and dimensional clearance through the riser pipe. Dynamic global riser analysis is conducted to ensure that there is adequate strength capacity with the wear liner in place. Furthermore, the riser system should tolerate loss of buoyancy through a flooded compartment in the aircan and a shut-in scenario where the drill string is supported by the surface BOP. Results from wear and fatigue damage due to vortex induced vibrations (VIV), vessel induced motion (VIM), drilling induced vibrations (DIV) and wave induced motions are presented based on design motions and monitoring data.