| 摘要 |
A method is provided for drilling of a well bore portion including a short radius curved section followed by a straight section. A drilling tool is provided having a first portion on which the drill bit is mounted and a second portion carrying the motor with a knuckle coupling therebetween. The short radius curved section is completed using the drilling tool with the knuckle coupling diverting to one side of the bore to steer the drill bit to the other side. After the curved section is complete the drilling is controlled in an accuratelystraight orientation by providing an eccentric collar which is attached onto thedrilling tool at a position adjacent the knuckle portion. The eccentric collar holds the drilling tool at a slight angle less than that during the curved section. Simultaneously with the rotation of the drill bit, the drill string, the tool and the collar are rotated more slowly about the longitudinal axis so as to constantly vary the angle of attack of the drill bit. In one arrangement, prior to attachment of the eccentric collar, a cylindrical or concentric collar is attached for drilling of a first short section of the horizontal portion. In an alternative arrangement, the eccentric collar has two flat sides which allow the collar and tool to rotate in a slightly curved bore without binding.
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