A new method which simplifies drilling operations in unstable formations has been tested by Statoil on the Brage field. This “liner drilling” solution makes it possible to operate with a well liner attached directly to a steerable drillstring, and represents a global innovation.
In conventional drilling, work has to halt while the string is pulled from the well and a liner set to prevent the borehole walls from collapsing.
“Setting liner while drilling means we don’t have to leave the borehole open and minimises the risk of collapse,” explained Geir Slora, head of drilling and well at Statoil.
In order to enhance the profitability of mature fields, Statoil is constantly working to improve their recovery factor. Liner drilling can contribute to these efforts. Developed in-house, the technology helps overcome the challenges of drilling in zones with lower pressure and difficult shale/coal layers, and in formations with varying flow and pressure regimes.
Many fields on the Norwegian continental shelf are mature, where Statoil must work within a narrow operational window with low margins.
“Liner drilling can be an important aid in such conditions,” said Slora. “It can also help to reduce the amount of time lost unnecessarily through drilling problems and technical sidetracks.”
The new technology – known officially as steerable drilling liner (SDL) – is the outcome of many years of collaboration between Statoil and equipment supplier Baker Hughes. It has been subject to extensive testing on land before being tried out in the North Sea on Brage. After a further test on Statfjord in January, SDL will be ready for use on other fields.