Multiple cam directional controller for steerable rotary drill

Details Multiple cam directional controller for steerable rotary drill Multiple cam directional controller for steerable rotary drill

1999-05-06

2001-05-22

Pezzuto, Robert E. (Department: 3671)

Boring or penetrating the earth

Means traveling with tool to constrain tool to bore along...

C175S061000

Reexamination Certificate

active

06234259

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates, in general, to a method and apparatus for controlling the direction of drilling a borehole. More particularly, the invention is directed to a method and apparatus for controlling the bending of a rotary drill stem with respect to the borehole to control the direction of drilling, and still more particularly to a multiple cam actuator for producing an accurate and controlled bending of a rotary drill stem.
One commonly-used method for controlling the direction of drilling a borehole is to utilize a “bent sub” at the bottom end of a drill stem, with a hydraulically-driven motor being mounted on the bent sub for operating the drill head. The bent sub positions the axis of the drill bit at a slight angle with respect to the axis of the drill stem and the hydraulic motor drives the drill bit at the angle of the bent sub, for example, at an angle of about one degree from the axis of the drill stem. The drill advances in the direction of the bend, thereby causing the borehole to curve in the direction of the bent sub and the angular position of the drill stem controls the angular direction of the curve. To drill a straight hole, the drill stem is continuously rotated while the drill bit is driven to thereby rotate the direction of the bent sub around the axis of the drill stem. This makes a slightly larger borehole, but causes it to be drilled in a straight line.
Alternatives to the foregoing technique for directional drilling include the technique described in British Patent 2,177,738, published Aug. 3, 1988. This patent discloses a steerable rotary drilling technique wherein a rotary drill stem passes through an enclosure tube, or housing, which is held against the sidewall of the borehole being drilled so that the tube does not rotate. Inside the tube, a system of hydraulically inflatable bags deflect, and thus bend, the drill stem in a controlled way with respect to the enclosure tube, and this bend causes the axis of the drill bit outside the housing to be angled with respect to the axis of the tube and thus of the borehole, causing the drill to advance in the direction of the bend to produce a curved borehole.
Another control mechanism for steerable rotary drilling systems is described in a publication of J. D. Barr et al entitled “Steerable Rotary Drilling with an Experimental System” presented at the 1995 SPE/IADC drilling conference held Feb. 28, 1995 (Paper Number SPE/IADC 29382). As there disclosed, a control mechanism selectively deflects drilling fluid against one of three radial pistons which extend out of the drill stem and against the wall of the borehole. The pistons are sequentially pushed outwardly as the drill stem rotates to press the drill stem away from a selected point on the borehole sidewall to thereby apply lateral force for steering the direction of drilling.
A third known control mechanism is illustrated in U.S. Pat. No. 5,168,941, wherein a stabilizer is anchored to the borehole wall. Drilling fluid actuates four pistons which press against the wall to adjust the location of the stem and to thereby apply lateral force to the drill bit to cause the borehole to curve.
Other control devices have been developed in the art to control drilling direction though the use of eccentric cams which bend the drill stem, as described, for example, in U.S. Pat. Nos. 5,307,885 and 5,316,090.
Each of the foregoing systems has been found to have problems, not only in producing an accurately controllable deflection in the drill stem, but in measuring the actual deflection produced by the control mechanism. Accordingly, there is a need for an improved control mechanism for directional drilling utilizing rotary drill stems.
SUMMARY OF THE INVENTION
Briefly, the present invention is directed to an improved steerable rotary drilling system having a directional controller mechanism incorporating a multiple cam actuator for bending a drill string to control its direction of drilling. In addition, the invention may include, in one embodiment, a detector mechanism for measuring the amount and direction of bending to provide feedback control of the drilling direction.
In general, the invention is directed to apparatus for controlling the direction of drilling in a borehole, and includes an elongated housing locatable in the borehole. A rotary drill stem extends coaxially through the housing and a first actuator set is mounted on the drill stem within the housing. A second actuator set is mounted on the drill stem adjacent the first actuator set, with actuators in the first and second sets being linked to each other for limited rotation relative to each other. Rotation of the drill stem causes the actuators to shift radially in opposite directions with respect to the axis of the drill stem to thereby shift the actuators alternately into and out of engagement with the housing to bend the drill stem with respect to the housing. Drivers are connected to selected actuators in each set to rotate them in order to change the bend in the drill stem.
In a preferred form of the invention, a directional controller mechanism for a rotary drill stem incorporates two axially spaced sets of actuators. These actuators preferably are coaxial, eccentric cams, and herein will be referred to as such, although it should be understood that the actuators can take other forms. Corresponding cams in the two sets are interconnected in pairs and are mounted on the drill stem to enable cams of one set to engage the interior of an elongated, directional enclosure tube, or control housing, surrounding a lower portion of the drill stem near its drill collar, while the cams of the other set are released from engagement. The control housing is located within the borehole being drilled, is restrained from rotating with respect to the borehole, and is secured at its upper and lower ends to the drill stem by suitable bearings which center the drill stem in the housing, with the actuator cams being located approximately midway between the housing ends. The cams are selectively rotatable with respect to the housing and the cams in at least some of the pairs of cams are rotatable with respect to each other. At least one cam engages the housing to shift the location of the drill stem laterally away from the axis of the housing, and thus of the borehole, to bend the portion of the drill stem which is in the housing. The bending of the drill stem causes the portions of the rotary drill stem which are outside the housing, and thus the drill bit carried by the drilling collar on the end of the drill string, to be angled with respect to the axis of the housing and the borehole, so that when the drill is operated, it tends to advance in the direction of the bend. By selective rotation of the cams, the desired amount and direction of borehole curvature can be obtained. To drill in a straight line, the cams are rotated to bring the axis of the drill stem into alignment with the axis of the housing, and thus of the borehole.
Preferably, two sets of side by side cams are provided, with each of the cams of one set being interconnected with a corresponding cam in the second set to form cam pairs. A first pair is fixedly mounted on the outer surface of, or is fabricated as a part of, the drill stem to rotate with the stem. The lobes of the first pair of cams are tiny, and their radii of greatest extension are offset 180° from each other. A second pair of cams is concentric with, and rotatably mounted on, the outer cam surfaces of corresponding cams of the first pair. The cams of the second pair are interconnected, or linked, so that their lobes are offset by an adjustable amount with respect to each other. A third or outer pair of cams are concentric with, and rotatably mounted on, the outer cam surfaces of corresponding cams of the second pair, with the cams of the third pair being interconnected so that their lobes are offset by an adjustable amount with respect to each other.
The first pair of eccentric cams is preferably integral with the drill stem and rotates with it to

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