The usual use of drill string deflecting apparatus to change the direction of a progressing bore hole involves application of orienting means with well bore communication means to rotationally control the scribe line of the deflecting apparatus. Occasionally, well drilling does not require the use of down hole communication apparatus. On such occasions, however, it is necessary to prevent the unplanned drift of the related drill string from established limits from the vertical.
Modern drill string deflecting apparatus can be included in the bottom hole assembly with little effect upon the technical and economical burden on the drilling activity. Economical well bore survey equipment is normally essential to verify compliance with well bore deviation limits. When the survey work indicates that the well is approaching an excess drift from vertical, selected drill string deviation influencing apparatus, often called kick subs, can be activated by manipulation of the drilling fluid flow controls.
As commonly practiced, deflecting the well bore is accomplished by orienting the drill string relative to earth azimuth and drilling ahead along the original well gage. That method involves expensive well bore communication equipment. The well bore communication process is well established in the art but involves the drilling operation in a technically burdensome activity. A considerable amount of drilling takes place without the well bore communication activity.
By selectively situating stabilizers and exercising bit load controls, a large amount of footage is drilled while maintaining the well bore within limited deviation from vertical. That process normally sacrifices some penetration rate, and is an expensive process. There is a need for processes that sacrifices less penetration rate.
Modern drill string deflecting apparatus can remain in place in the bottom hole assembly without reducing penetration rate and with little technical burden on the drilling activity. Further, modern deflecting apparatus can be activated from the rig floor by manipulation of the drilling fluid flow rate controls, usually just the mud pump drive throttle controls.
Simple apparatus for use in confirming the deviation of the well bore from vertical has been in use for many years and is usually present on the drill site by regulation compliance needs.
If deviation from vertical, at a selected location, in the progressing well bore is small the bore straightening pendulum influence is slow to take effect and often requires reduced bit loads. The result is reduced penetration rate lasting for an extended period. Further, the required positioning of stabilizers for maximum pendulum influence often invites lateral influence of the drill bit caused by formation peculiarities.
The presence of deflecting apparatus near the drill bit, and the presence of well bore survey equipment makes possible a form of well bore control that is economical in terms of required equipment and loss of time.
The deflecting apparatus, once activated, will tend to enlarge the well bore as drilling progresses. Normally, the bit load can be maintained with little reduction of the penetration rate, after the deflecting apparatus has operated with reduced bit load for a short period of time. The well bore will initially be enlarged with reduced bit load, then the drill bit will walk around the available drilling face with increased bit load.
When sufficient enlarged length of bore is produced, the drill string can be lifted to allow the drill string pendulum effect to drop the bit to the low side of the enlarged hole. The kick sub can then be straightened to allow the bit to proceed along the changed extended axis of the lower end of the drill string. The progressing well bore then is drilled along a line with the departure from the vertical reduced relative to the previous well axis. When such practices are used, a substantial reduction in cost per foot of hole can be realized.
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