Deepwater Development Update
As part of a new development offshore Ghana, Tullow Oil plc wanted to look at ways to reduce downhole tool failures while still maintaining time-efficient drilling. This led to deployment of the Tomax AST tool.
Delays from downhole failures are costly. Even more costly are the same failures when they happen on a modern drillship far out in deep waters. Tullow Oil wanted to be systematic about their improvements. This meant documenting “cause and effect” so that good solutions could be safely repeated in future wells in order to achieve the goal of shoe-to-shoe drilling.
An 8¼” XC-AST was picked up for test in a dedicated 12¼” section. The tool was combined with already proven choices for BHA and parameters. The combination enabled the driller to balance minimal risk versus speed through all the different sequences of geology. The section was consequently drilled shoe-to-shoe in one run. This was a first for the development.
The new method for drilling yielded a significant improvement: the torsional stick-slip vibrations stayed in green throughout the section. This confirms a very low risk of failure. At the same time, drilling efficiency was up by 36% over a comparable interval, identified by increasing shale content.