Abstract
AbstractThe Åsgard field in the Norwegian sea contains hard, abrasive, and high temperature formations and the reservoir had never been successfully drilled in a single slimhole run over 10 years. Thorough engineering analysis, the application of lessons learned, and the introduction of new generation technology produced a series of improvements. These advances define a sustainable and systematic approach to efficient, cost-effective hard rock drilling in the Norwegian Sea and elsewhere. The method was to define the limitations of the existing approach and then iterate improvements to the system to increase performance. The first step was to define the existing operating envelope: offset data – drilling, downhole, and post-well analysis – was reviewed and weak points were identified. Then, using the most appropriate lessons from hard rock environments worldwide, initial design changes were made to the drilling approach and procedures. These changes delivered the first failure-free well in the field. New technology was then introduced to expand the drilling envelope further and this culminated in the first single run slimhole section in the field. Flat time was drastically reduced, while ROP and borehole quality were improved. Through scrutiny of drilling dynamics, high frequency torsional resonance (HFTO) was revealed to be driving system mechanical inefficiencies. Log analysis enabled the correlation of the onset of HFTO to lithology type, and new drilling parameter limitations – principally management of Weight On Bit (WOB) – were then defined. Real-time drilling optimization engineers were enlisted to support this approach. Rock strength analysis and post-run equipment inspection determined the need for more durable bit and Bottom Hole Assembly (BHA) designs. A custom drill bit was designed and a ruggedized, new generation Rotary Steerable System (RSS) and Measurement and Logging While Drilling (MWD/LWD) suite introduced. Within the established operating framework, this new technology enabled enhanced drilling parameters to be applied and resulted in a 53% improvement in penetration rate. High density survey data from the new MWD/LWD platform showed that the new generation drilling technology delivered an extremely high quality wellbore, where the cumulative tortuosity was within 5% of the theoretical well plan. This allowed the installation of the completion string in a new record time, reducing the technical limit. Overall, flat time was reduced by 56% and then 76% versus the offset average. Robust, new generation technology and a rigid adherence to system limits as defined by advanced engineering analysis provided a framework for rapid continuous improvement and a blueprint for repeatable, efficient performance. This can be used to drive efficiency improvements in similar offshore hard rock environments elsewhere.