During well construction, it is important to know when a bit is damaged to the point where it must be tripped out and replaced with a new bit. Continuing to drill with a damaged bit or pulling out a bit prematurely are both bad decisions leading to increased drilling costs. A bit pull advisory system was therefore developed and deployed in the field to help the rig crew make better informed bit pull decisions.

A bit degradation metric was first developed to estimate the wear on the drill bit as it is drilling. This bit degradation metric utilized a physics-based model to be generalizable both for vertical as well as horizontal wells. Next this metric along with other trends in data were combined using a Bayesian network to arrive at a bit effectiveness belief. This was then further combined with calculations of the time to trip out a damaged bit and replace it with a new bit, to arrive at bit pull beliefs for various scenarios of expected future ROP and distance to total depth (TD).

The bit degradation metric was first applied offline on 80 historical wells that consisted of wells drilled in Egypt, North Sea and the US land, and verified to a high degree of accuracy. It was then integrated into a drilling data aggregator and deployed in the field. The physics-based model utilized in the calculation of the bit degradation metric required contextual data, which was automatically routed to the data aggregator from various data sources. The bit pull beliefs for a range of expected ROPs and distance to TD were made available both as channels that can be visualized in vertical charts as well as a heat map. When a bit pull belief suggested a trip out, the driller was first asked to monitor for drilling dysfunctions such as stick slip, bit balling, whirl, etc., and attempt to correct it. Failing that, the bit was to be pulled out. This system is now operational on rigs in Egypt, North Sea and the US, and the response from the field personnel has been positive to date.

This is the first drill bit damage tracking advisory that has been deployed on a rig site data aggregator. Using the bit degradation metric and the bit pull beliefs, the rig site team is always able to determine the extent of damage to the bit and whether the bit must be pulled out or not. The system thus helps in reducing ILT and NPT costs by reducing the time drilled with damaged bits and eliminating premature trips out.

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