In the 1st and 2nd reports, by an experimental reappearance of the crooked-hole phenomenon of a deep boring the mechanism of the crook and the influences of the circulating rate of water, the wearland of tips of the bit and the thrust on the bit were described, by means of the inclined angle of 30° of th e boundary of layers.
In this paper, the relation between the crook of the borehole and the inclined angle of the boundary of layers were investigated, by the artificial rock samples changing the inclined angles as 15°, 30°, 45°, 60°, 75°.
Then, the followings were obtained within this experiment.
(1) In consequence of change of the inclined angle the drift angles showed different values at the larger wearland of tips. And, at the inclined angle of 45 the drift angle reached even the value of 10°.
(2) The direction of the crook of borehole was recognized towards the up-dip side even if the large inclined angle of 75°.
(3) The twisted angle as the value of the clock-wise deflection of the orientationwas considerable in any cases of inclinations in this experiment, and at the angle of 75° this value was shown up to 112°.
(4) Then, the larger the inclined angle was, the larger the horizontal shift of borehole was, and at the inclination of 75° the horizontal shift was amounted up to 28mm.
(5) Here, an index for the phenomenon of a dogleg was proposed and this was large at the smaller angle of the inclination in this experiment.
