A drilling fluid comprising a pyruvate-free xanthan, which may be an acetate-free pyruvate-free xanthan, and a high density calcium-based brine. The x-ray detector is accommodated on the C-arm so that translation movements can be executed with the x-ray detector in relation to the C-arm. The pointed structures raised from grooves carved into the surface of the sheet material by means of a set of teeth carried on a knife element.