Borehole Deviation Facility
Drilling in conjunction with construction and operation of a repository for spent nuclear fuel at Forsmark requires careful control of borehole geometry in various applications.
Foreseen pilot holes for deposition tunnels, up to 300 m long, where the boreholes are required to stay within the tunnel perimeter calls for careful control of the drilling process. This requires development not only of drilling methodology but also of instruments and methodology for providing the necessary steering and successive verification of borehole geometry. To this end SKB has devised a facility where indirect deviation measurements can be verified relative to the known geometry of a simulated borehole on ground surface.
The 300 m long near horizontal simulated borehole was constructed during 2013 on the Äspö island. The equipment consists of a plastic tube anchored to the rock. The tube, which essentially follows ground surface topography, has been carefully surveyed geodetically. In order to allow for testing adapted to the very strict requirements of the KBS-3H project, the facility features a 60 m segment with very small scale variation and undulation. The facility is used by SKB and can possibly be used by SKB’s external partners as well.
Initial tests of deviation equipment of different types, including magnetic tools, gyro based tools have been carried out during 2014. These measurements have provided important results that have been used in the planning and execution of recently concluded drilling operations at the Äspö HRL.
Experiences gained during the initial testing will be used to improve the facility and the methodology for carrying out and comparing results and different instruments. These results will guide SKB in the selection of methodology and equipment to be employed in the planned repository.