While offshore intervention on subsea equipment is quite common, the increasingly deeper water operations require light weight intervention systems while meeting safe and stringent operating specification. For these new deep offshore challenges, the conventional risers are becoming a more costly and less desirable solution.
Starting with a recollection of the main drivers that motivated the development of drill pipe riser intervention systems (DPRISi ), the paper details the technical and economical challenges in West Africa that have led to the design of such a solution. When non-productive time and financial aspects are taken into account, it makes sense to develop a dedicated system in order to provide fast and reliable intervention.
Depending on the field requirements, two different types of drill pipe riser systems using a proprietary double shoulder connection were used by operators. A first solution was developed in 1999 featuring a seal ring close to the external shoulder. Subsequently, a new solution featuring a gas-tight metal to metal seal on the pin nose was developed in order to address increasingly demanding and challenging operations.
Intensively used in West Africa since 1999, the solution using the seal ring has shown robustness and reliability while being used for several projects in Angola such as Girassol and Rosa and now GirRI. The paper draws a summary of these operations and the feedback on the field use and maintenance. Also it emphasises the successful qualification process for the metal to metal seal solution that has been used in offshore Nigeria since 2010 for the USAN project.