The Upper Cretaceous is a challenging drilling environment in Santos Basin, offshore Brazil. The lithology consists of highly intercalated layers of sandstone, siltstone and conglomerate from Santos and Jureia Formations. These formations are drilled vertically in 17 ½" intermediate hole and the length of the section varies from 1600 m up to 2000 m. Optimizing the drilling efficiency in this section is crucial to reducing drilling costs and non-productive time. During a recent exploratory campaign in Santos Basin, severe levels of shocks and vibrations were encountered while drilling this large and intercalated hole section, resulting in a low rate of penetration, premature bit wear, damaged tools, unplanned trips and drill string failures. Three to four bit runs were required to reach section TD. Post job information and drilling data were reviewed by an integrated operator-contractor team. A detailed engineering analysis of bit, BHA design and drilling mechanics was conducted to address the challenges of this section and propose a new approach to the drilling process. The key was the determination of the best combination of WOB and RPM to drill the different lithologies, together with more stable PDC bits, use of downhole motors and combined with specific operational procedures to mitigate shocks and vibrations. The proposed changes in bit selection and BHA configuration, drilling parameters and procedures, real-time monitoring and training have been successful. For the first time in the drilling campaign in Santos basin, it has proved possible to drill the 17 ½" hole in one bit run. The section was finished without any incident, under budget and under time. The improvement in drilling performance achieved with the implementation of this engineering study helped the operator to mitigate shocks and vibrations and save money, thus ensuring a more efficient drilling operation and preventing further drill string failures.
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