Abstract

Interbedded formations are challenging to drill due to its potential to trigger torsional instability issues while drilling at low depth-of-cut (DOC), which could damage the bit due to impact and result in low penetration rate or an undesired trip. Wells drilled in the Guyana-Suriname Basin face a similar challenge as the wells penetrate interbedded shale and carbonates, causing conventional polycrystalline diamond compact (PDC) bits to lose their cutting efficiency due to impact damage while drilling the hard, interbedded formation.

Using a detailed bench-marking methodology, offset drilling data was analyzed and the results were utilized to optimize bit design to meet these challenges. Mechanical specific energy (MSE), which quantifies drilling efficiency, indicates formation changes and signals the advanced dull condition or damage. When coupled with dull bit forensics, MSE provides insight for iterative bit design optimization to mitigate drilling challenges.

The outcome of a detailed benchmarking process led to the selection and deployment of a 12ΒΌ-in. hybrid bit to drill directionally through interbedded formation, which significantly improved drilling performance and bit durability. The hybrid bit combined PDC and tungsten carbide insert (TCI) rolling cutting elements and delivered balanced aggressiveness to improve torisonal stability. Post-well analysis showed rolling DOC control offered by the hybrid bit delivered higher penetration rate. The comparison of the drilling mechanics of the hybrid versus PDC highlighted limited drilling efficiency of PDC bits in interbedded formation. The hybrid bit drilled 54% more carbonates than the best PDC offset run. Drilling dynamics data also highlighted lower levels of vibrations with the hybrid bit. In addition, the hybrid dull condition was better than the PDC bits, suggesting improved durability compared to the previously-used PDC bits.

This paper demonstrates time and depth based surface and downhole drilling data, when supplemented with rock strength analysis using a suitable benchmarking process, can provide insight about drilling mechanics. When matched with an application specific bit, it leads to sustained drilling performance improvement.

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