Introduction of New Drilling Technology Improves Performance of Mature North Sea Assets

Abstract

Abstract The Central North Sea (CNS) Cretaceous formations are notoriously difficult for performing directional drilling operations. Oriented drilling using bent housing steerable motors is troublesome and rate of penetration is unacceptably slow with rotary steerable systems. This has historically resulted in well trajectories being planned with minimal directional course changes through these sequences and, when directional course changes are absolutely required, oil based mud is often required to facilitate oriented drilling. With many assets in the Central North Sea reaching maturity, directional drilling course changes in the Cretaceous has increasingly become a necessity to access remaining targets. Talisman Energy (UK) Limited acquired several CNS mature assets in the period 1997 – 2005. A challenge faced by the operator was to improve directional drilling control and overall drilling performance through the CNS Cretaceous while simultaneously moving away from oil based mud requirements. A new generation rotary steerable system which integrates a performance drilling motor with a high speed rotary steerable tool was introduced to meet this challenge. By applying this new system coupled with the latest steerable drill bit technology, precise three dimensional trajectories are now being drilled at more than double the offset rates of penetration & water based mud can now be used more frequently. The results have been easier access to remaining reserves, a dramatic reduction in drilling time, lower environmental impact and overall reduced cost and risk. This paper describes the drilling conditions in the CNS and the new drilling technology applied. It also describes the challenges encountered applying new technology on cost sensitive mature assets, procedures put in place to minimise operational risk while introducing the new system and a comparison of performance now compared with that of offset wells.