This paper describes the strategy, design and the drilling fluid and cement operations in the first two wells drilled with Coil Tubing on the Gullfaks field. The strategy and design is explained in great detail. Excellent hole cleaning was achieved in both wells.
A serious problem of differential sticking was eliminated by a radical change in drilling fluid strategy and design. It was possible to successfully drill a 3 ¾" hole, log and run/cement a 2 7/8" liner at a maximum inclination of 122°.
A virtually solids free Potassium Formate Brine/Polymer drilling fluid with a density from 1.50 – 1.56 g/cc was used. The flow properties of the drilling fluid is characterised by a very low fluid loss due to a high extensional viscosity, a low viscosity at all shear rates and a low degree of shear-thinning.