Boring or penetrating the earth – Processes – Boring curved or redirected bores
Reexamination Certificate
2000-10-04
2002-11-26
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Processes
Boring curved or redirected bores
C166S066000, C175S026000, C175S045000, C175S073000, C175S279000
Reexamination Certificate
active
06484819
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of borehole drilling, and particularly to systems and methods for controlling the direction of such drilling.
2. Description of the Related Art
Boreholes are drilled into the earth in the petroleum, gas, mining and construction industries. Drilling is accomplished by rotating a drill bit mounted to the end of a “drill string”; i.e., lengths of pipe that are assembled end-to-end between the drill bit and the earth's surface. The drill bit is typically made from three toothed cone-shaped structures mounted about a central bit axis, with each cone rotating about a respective axle. The drill bit is rotated about its central axis by either rotating the entire drill string, or by powering a “mud motor” coupled to the bit at the bottom end of the drill string. The cones are forced against the bottom of the borehole by the weight of the drill string, such that, as they rotate about their respective axles, they shatter the rock and thus “dig” as the drill string is turned.
Boreholes are frequently drilled toward a particular target, and thus is it necessary to repeatedly determine the drill bit's position. This is typically ascertained by placing an array of accelerometers and magnetometers near the bit, which measure the earth's gravity and magnetic fields, respectively. The outputs of these sensors are conveyed to the earth's surface and processed. From successive measurements made as the borehole is drilled, the bit's “present position” (PP) in three dimensions is determined.
Reaching a predetermined target requires the ability to control the direction of the drilling. This is often accomplished using a mud motor having a housing which is slightly bent, so that the drill bit is pointed in a direction which is not aligned with the drill string. To effect a change of direction, the driller first rotates the drill string such that the bend of the motor is oriented at a specific “toolface” angle (measured in a plane orthogonal to the plane containing the gravity vector (for “gravity toolface”) or earth magnetic vector (for “magnetic toolface”) and the motor's longitudinal axis). When power is applied to the motor, a curved path is drilled in the plane containing the longitudinal axes.
One drawback of this approach is known as “drill string wind-up”. As the mud motor attempts to rotate the drill bit in a clockwise direction, reaction torque causes the drill string to tend to rotate counter-clockwise, thus altering the toolface away from the desired direction. The driller must constantly observe the present toolface angle information, and apply additional clockwise rotation to the drill string to compensate for the reaction torque and to re-orient the motor to the desired toolface angle. This trial and error method results in numerous “dog leg” corrections being needed to follow a desired trajectory, which produces a choppy borehole and slows the drilling rate. Furthermore, the method requires the use of a mud motor, which, due to the hostile conditions under which it operates, must often be pulled and replaced.
SUMMARY OF THE INVENTION
A system and method of drilling directional boreholes are presented which overcome the problems noted above. The invention enables a desired drilling trajectory to be closely followed, so that smoother boreholes are produced at a higher rate of penetration.
The invention employs a controllable drill bit, which includes one or more drilling surfaces which are dynamically positionable in response to respective command signals. Instrumentation located near the bit measures present position when the bit is static, dynamic toolface and drilling surface position information when the bit is rotating, and stores a desired trajectory. This data is processed to determine the error between the present position and the desired trajectory, and the position of one or more of the bit's drilling surfaces is automatically changed as needed to make the bit dig in the direction necessary to reduce the error.
The controllable drill bit is preferably made from three cone assemblies, each of which includes a cone and an eccentric cam that rotate about a common axis. In response to a command signal, the cam is either locked to the cone to cause concentric rotation of the cone, or locked to the axle to cause eccentric rotation of the cone—which causes the bit to dig in a preferred direction.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.
REFERENCES:
patent: 3825081 (1974-07-01), McMahon
patent: 4040003 (1977-08-01), Beynet et al.
patent: 4491186 (1985-01-01), Alder
patent: 5160925 (1992-11-01), Dailey et al.
patent: 5314030 (1994-05-01), Peterson et al.
patent: 5341886 (1994-08-01), Patton
patent: 5467832 (1995-11-01), Orban et al.
patent: 5813480 (1998-09-01), Zaleski et al.
patent: 5880680 (1999-03-01), Wisehart et al.
patent: 6109370 (2000-08-01), Gray
patent: 6230822 (2001-05-01), Sullivan et al.
patent: 3704077 (1987-08-01), None
patent: WO 93/12319 (1993-06-01), None
LandOfFree
Directional borehole drilling system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Directional borehole drilling system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Directional borehole drilling system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2923438