Patent ID: 9080389
Filing Date: 2015-07-14
Classification: E21B

Abstract:
1. A method for drilling shafts in ground layers consisting of rock, clay and/or related materials, comprising arranging a borehole casing in the ground in a manner such that it admits substantially no water on its underside, lowering into the borehole casing a hollow drill string provided with a drill head with cutting tools, arranging a water column in the borehole casing, then setting the drill string into rotation in the borehole casing so that ground material is dislodged by the cutting action of the cutting tools and is discharged using a flow maintained by the water column in the hollow drill string, wherein at the position of the drill head a first fluid is injected under a first pressure of at least 200 bar into the ground layers by one or more nozzles, the nozzles being positioned such that they inject the first fluid outward into ground layers situated at a greater depth than a lower outer end of the borehole casing.