| 20090065258 | METHOD AND APPARATUS FOR DIRECTIONAL DRILLING WITH VARIABLE DRILL STRING ROTATION - Apparatus and methodology is provided for directional drilling which avoid the effects of static friction between the drill string and the borehole. The drill string is rotated continuously in one direction during rotating drilling and during steering. During steering, the rotary speed of the drill string is varied within a revolution and substantially similarly for each of a plurality of subsequent revolutions. The drill string is be rotated very slowly when oriented at or near the desired orientation to achieve the desired change in direction and then rotated much faster during the balance of each revolution. This angular velocity profile results in drilling at or near a desired orientation for a high percentage of the time it takes for each revolution. Changes in an effective tool-face orientation can be effected by shifting the phase of the velocity profile. | 03-12-2009 |
