The increasing complexity of deepwater Bottom Hole Assemblies (BHAs) requires a complete systematic approach to each phase of the drilling process: pre-job planning, execution and evaluation. This approach was successfully applied to a recent multi-well project in the Gulf of Mexico, whose vertical 12¼ in x 13½ in sections were historically plagued by shocks and vibrations while drilling. The root cause of inefficient drilling performance could not be accurately determined based on drilling data, but severe vibrations resulted in multiple downhole tool and BHA component failures.
With the implementation of a complete, holistic approach to the drilling system, the drilling proceeded with no downhole tool failures and a significant reduction in drilling time and costs. The key to these successes were the multistage preparation process that was utilized, which included:
A detailed analysis of all the offset data available for the same field and for fields with similar lithologies and formation properties. A rock strength analysis based on Logging While Drilling (LWD) data and Compressive Confined Strength (CCS) measurements. A bit and reamer matching process taking into account CCS, lithology, directional profile and cutters layout while matching the performance criteria for both drill bit and underreamer.
Advanced tools and technology, including critical speed analysis and asymmetric vibration tool placement, were applied and supported by high-frequency downhole dynamics memory data with corresponding post-run drilling performance and vibration analysis. Some of the major contributors to the successful application were the designed-for-purpose engineered BHA and optimized operational environment.
This approach can be applied to borehole enlargement wells, as well as vertical, directional and horizontal wells. The analyses of the measurements gathered during all phases of the project, including a description of the obtained results, are discussed in detail. The results highlight a consistent improvement in drilling performance for the 12¼ in x 13½ in well section, where vibrations were the main limiting factor. Efficient drilling performance is achieved by implementing this complete approach to the deepwater drilling system and these engineering solutions for vibration mitigation, increasing ROP and improving BHA integrity and wellbore quality.
