In the Norwegian sector of the North Sea west of Bergen, unstable shales, coals and paleosols in the reservoir have regularly resulted in problems when running liner. Conventional mitigations learnt from previous wells or taken from similar fields have been adapted, but running 7″ liners successfully to TD at the first attempt has continued to be a challenge and it is desired to drill longer horizontal wells through these unstable formations in order to improve the recovery factor. New mitigations are therefore considered, including a turbine power shoe that had been used successfully in other countries.
The turbine power shoe provides the ability to rotate a reamer shoe without rotating the whole string from surface, while it requires limited changes to the liner string and running parameters. It is an additional tool to cross ledges and unstable intervals. The tool has been used in four wells in Gullfaks Satellites and Oseberg fields. In all these cases, the turbine shoe was activated and the liner was run to TD. Therefore the turbine power shoe will continue to be considered as an additional mitigation for running liner at high inclination through unstable formations.