Abstract
Rig costs account for a substantial part of the total cost of an offshore field development project. Systems and methods that can reduce the non-productive time are therefore of interest to operators. In deep and ultra-deep waters, the duration of drilling campaigns with multiple, closely located wells may potentially be reduced by optimizing equipment-retrieving procedures between moving from one drilling location to another. This may be achieved by not retrieving the whole drilling riser and the BOP to the surface. Instead, retrieving just a few joints and navigating the drilling rig with the drilling riser and BOP suspended may save several days of rig time.
Previous works on this topic have investigated the riser response during the move and delineated under which environmental conditions (waves and current) this operation may be safely executed. The axial displacement of the riser column may be of concern, and it has been presented that the hang-off condition may substantially influence the response of the riser. Instead of looking at the riser hanging either from the spider-gimbal or from the tensioners, this work proposes to use the active heave compensation system of the drillstring to more efficiently decouple motions of the rig from the riser during the move. Thus, mitigating the riser response and enabling the navigation with the suspended riser and BOP to take place under broader environmental conditions.
A commercial program for computational simulations of the riser dynamic responses was used in the study presented in this paper. A representation of the active heave compensation drilling system and the tool used to achieve this purpose were added to the model. The responses of a typical riser used in deep water were determined under several environmental conditions, and the responses of different hanging systems were compared. Results indicate that the proposed approach for suspending the riser may decrease the dynamic forces and stresses during the rig move. The ability of the modeled rig equipment to withstand the move was also investigated.
