Patent ID: 7225887

Claim:
A method of drilling a borehole into an earth formation using a drill string having an upper part and a lower part which is more flexible than the upper part, the method comprising: drilling a first section of the borehole; drilling a second section of the borehole from said first borehole section, said second section extending at a selected inclination angle relative the first section, wherein during drilling of the second section the drill string is lowered through the borehole in a manner that the upper drill string part remains in the first section and the lower drill string part extends into the second borehole section, the first borehole section being substantially straight and the second borehole section being a curved section, wherein the lower drill string part is guided from the first borehole section into the second borehole section by means of a tubular housing or a tubular element arranged in the first borehole section, said tubular housing or tubular element having a passage through which the drill string extends, said passage having a lower end part directed towards the second borehole section, wherein the upper drill string part is provided with a downhole motor, which rotates the lower drill string part during drilling of the second borehole section, and wherein the lower drill string part is provided with a drill bit which is tilted relative to the longitudinal axis of the lower drill string part, wherein an orienting shaft extends between the downhole motor and the drill bit for orienting the drill bit in the borehole, and wherein the method further comprises rotating the orienting shaft over a selected angle so as to orient the drill bit in the second borehole section in correspondence with the desired direction of drilling of the second borehole section.