US20120199399A1 - Casing rotary steerable system for drilling - Google Patents

Abstract

A system for drilling a deviated borehole, comprises a drill string, a bending mechanism supported on the drill string, a drill bit supported on the bending mechanism such that the axis of the bit does not align with the axis of the drill string where it connects to the bending mechanism, and a liner supported on at least one of the bit and the drill string and having upper and lower ends, wherein the bending mechanism is disposed within the liner such that the upper and lower liner ends are not co-axial.

Description

RELATED CASES
• Not applicable.
FIELD OF THE INVENTION
• The invention relates to a casing-drilling system with directional capabilities. More particularly, the present invention relates to a system in which a bending mechanism supports the drill bit and extends through a casing or liner such that the casing or liner is bent by the bending mechanism.
BACKGROUND OF THE INVENTION
• In oil and gas drilling operations it is often desirable to change direction in the course of drilling. Generally, the goal is to change the direction in which the drill bit at the lower end of a drill string drills, so that it does not drill along the central longitudinal axis of the lower part of the drill string. Many drilling systems and methods have been developed for this purpose. These include “point-the-bit” systems, in which the axis of rotation of the drill bit is deviated from the axis of the bottom hole assembly (BHA), such as by including a bend in the BHA itself, and “push-the-bit” systems, in which eccentric stabilizers or eccentric actuators push the bit into a desired orientation with respect to the axis of the BHA.
• Oil and gas wells are typically drilled using a drill string that supports and propels the bit. After a desired length of hole has been drilled, the drill string is typically removed and a casing or liner is cemented into the hole. “Liner” refers to casing that is set below a preceding length of casing. Unless expandable tubulars are used, a liner will have a smaller diameter than the casing or liner above it. Liners are typically suspended from the upper string by a hanger device. For purposes of the following discussion, casing and liner are considered interchangeable.
• Because of the significant time and effort required to pull the drill string out of the hole and place and set a length of casing, a modification of conventional drilling has been developed, in which a length of casing is used as the drill string. In this type of operation, termed “casing drilling,” the bit is mounted at the lower end of the casing string and rotation of the bit is provided by rotating the casing string. Once the desired depth has been reached, the bit is disconnected from the casing and retrieved through the casing to the surface, whereupon the cycle can be repeated. In some instances, the bit may be directly attached to the casing string and left in place. In these cases, the bit is typically drilled out by the next smaller sized bit.
• When it is desired to combine the concepts of directional drilling and casing drilling, various aspects of the operation make it difficult to combine the mechanical systems that accomplish each, as mentioned in U.S. Pat. No. 7,086,485. It is therefore desired to provide a system that effectively allows directional casing drilling without requiring cumbersome or expensive equipment downhole.
SUMMARY OF THE INVENTION
• In accordance with preferred embodiments of the invention there is provided a system for drilling a deviated borehole, comprising: a drill string, a bending mechanism supported on the drill string, a drill bit supported on the bending mechanism such that the axis of the bit does not align with the axis of the drill string where it connects to the bending mechanism, and a liner supported on at least one of the bit and the drill string and having upper and lower ends, wherein said bending mechanism is disposed within said liner such that the upper and lower liner ends are not co-axial.
• The bending mechanism preferably contacts the inside of the liner at at least three axially spaced-apart locations, and may include a stabilizer. The system may include at least one sleeve surrounding the bending mechanism such that said sleeve transfers a bending force to the liner. The lower end of the liner may be attached to the bit and the liner may rotate with the bit.
• As used in this specification and claims the following terms shall have the following meanings:
• With respect to a borehole, “above” shall refer to positions that are relatively closer to the surface and “below” shall refer to positions that are relatively closer to the bottom of the borehole, even if the borehole is deviated or horizontal.
• As mentioned above “casing” and “liner” may be used interchangeably. Thus, references to “casing drilling” or “liner drilling” are intended to apply equally to both types of drilling.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a more detailed understanding of the invention, reference is made to the accompanying Figure, which is a schematic illustration of a system constructed in accordance with the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
• Referring to the Figure, acasing drilling system10 in accordance with a preferred embodiment extends from the surface (not shown) into aborehole12 in aformation14. A portion ofborehole14 abovecasing drilling system10 may be cased with a previously-placedcasing string16.Casing drilling system10 includes adrill string18, aliner string20, amandrel22, upper andlower latches30,32, respectively, aneccentric bearing34, and abit24. In other embodiments,bit24 may be supported on a mandrel (not shown).
• In the embodiment shown, during drilling, torque is applied todrill string18 at the surface, transmitted fromdrill string18 toliner string20 at the top ofliner20, and fromliner20 tobit24. In some instances, a linerhanger running tool25 may be included between the liner and the drill string, so that torque is applied to the bit via a path that includesdrill string18, linerhanger running tool25, andliner20, as indicated byarrows27,28, and29. Alternatively, torque can be transmitted fromdrill string18 tobit24 at the bottom ofliner20. In still other embodiments (not shown), torque can also be transmitted from the drill string to a torque sleeve, from the sleeve to the liner, and from the liner to the bit. In the discussion that follows, it will be understood that the concepts relating to the invention are not dependent on the mechanism by which torque is transmitted to the bit. It will be understood that mud motors, such as are known in the art, may be used as another source of torque and in some instances could cause the bit to rotate faster than the liner.
• Regardless of the path, torque is ultimately transmitted tobit24, causingbit24 to rotate and advance throughformation14.Liner string20 advances with the bit.
• Liner string20 andbit24 are preferably connected by a releasable mechanism that allows torque to be transmitted fromliner string20 tobit24 during drilling and also allowsbit24 to be disconnected fromliner string20 when the desired hole depth has been reached. An example of a suitable mechanism for this function is sold under the name “E-Z Case” by Hughes Christensen Company of Houston, Texas. As mentioned above, in other embodiments, the bit may be left in place. Similarly, upper andlower latches30,32 andeccentric bearing34 are supported in the liner in a manner that allows them to be retrieved.
• In order to drill a deviated hole, it is necessary to apply a lateral force that deflects the bit, so that the bit cuts along a path that is different from the axis of the hole immediately above the bit. As mentioned above, in non-casing-drilling systems, push-the-bit and point-the-bit systems rely on mechanisms that push against the formation so as to apply an opposing force to the bit, forcing its axis to differ from the main tool axis.
• According to preferred embodiments of the present invention, a lateral force is applied to the bit by a three-point system that is contained withinliner string20. The three-point system may includeupper latch30,lower latch32, andeccentric bearing34. As shown in the Figure, upper andlower latches30,32 may holdmandrel22 in a central position withinliner string20, whileeccentric bearing34 has an off-center bore through whichdrill string18 passes. The eccentricity of the bearing is illustrated byarrows44,46, which are unequal in length.
• Unlikeliner string20, bearing34 does not rotate relative to the formation. Instead, it is provided with means that cause it to rotate aroundmandrel22 in a direction opposite to the direction of rotation ofliner string20, as indicated at37. Such a device is preferably an actively powered device that is capable of sensing its position and can apply counter-rotation to theeccentric bearing34, allowing it to remain substantially motionless with respect to the borehole. Such devices are known and are commercially available.
• For example, rotation ofbearing34 can be provided by an actively powered device applying counter-rotation to thebearing34, thereby allowing it to remain rotationally motionless with respect to the earth. One example of such a device is a hydraulic power unit. In contrast, latches30 and32 can rotate in a 1:1 ratio withliner string20.
• Because of the off-center support provided byeccentric bearing34,mandrel22 tends to be pushed toward one side withinliner20. The competing forces exerted by eccentric34 bearing and latches30 and32cause mandrel22 to bend in one direction andliner20 to bend in an opposite direction. The degree bending of each component will depend on the relative stiffnesses ofmandrel22 andliner20. Ifmandrel22 is sufficiently stiff relative toliner20,liner20 can be bent by a desired amount, with the result that both the distal end ofliner20 andbit24 will be pointed in a desired direction.
• Becauseeccentric bearing34 does not rotate relative toformation12, the direction in which bit24 is pointed will remain substantially constant. Asliner string20 rotates, it will undergo cyclic or periodic deflection. For this reason, it may be desirable to consider material selection and expected stress levels when designing the components of the system, as is known in the art. Thus, in one exemplary embodiment,liner string20 comprises a composite material with a low transverse stiffness, whilemandrel22 comprises a relatively stiff material, such as beryllium, aluminium-beryllium composites, beryllium titanium composites, and the like.
• It will be understood that theeccentric bearing34 can be replaced with a set of selectively retractable pads (not shown) that periodically extend and retract as the liner rotates and serve to keep the eccentricity of the bending mechanism oriented to a constant azimuth.
• If desired, one ormore stabilizers40 may be provided at various points along the liner string.Stabilizers40 serve to center the equipment in the borehole and reduce movement of the tool during drilling. In preferred embodiments, at least one stabilizer is included near the upper end ofliner string40. It is preferred thatstabilizers40 be close toupper latch30 so as to maximize the effect of the bending.
• It will be understood that the preceding discussion has described the concepts of the present invention with respect to certain preferred embodiments and that variations in the components of the system can be varied without departing from the scope of the invention, which is set out in the claims that follow.

Claims (8)

1. A system for drilling a deviated borehole, comprising:

a drill string;

a bending mechanism supported on the drill string;

a drill bit supported on the bending mechanism such that the axis of the bit does not align with the axis of the drill string where it connects to the bending mechanism; and

a liner supported on at least one of the bit and the drill string and having upper and lower ends,

wherein said bending mechanism is disposed within said liner such that said upper and lower liner ends are not co-axial.

2. The system according toclaim 1 wherein the bending mechanism contacts the inside of said liner at at least three axially spaced-apart locations.

3. The system according toclaim 1 wherein the bending mechanism includes a counter-rotating device that maintains the orientation of the bending substantially fixed relative to the borehole.

4. The system according toclaim 1 wherein the bending mechanism includes a mandrel that is stiffer than the liner.

5. The system according toclaim 4 wherein the mandrel is constructed of a material that comprises beryllium.

6. The system according toclaim 1 wherein the lower end of the liner is attached to the bit and the liner rotates with the bit.

7. The system according toclaim 1 wherein the upper end of the liner is attached to the drill string.

8. The system according toclaim 1, further including a stabilizer disposed between the liner and the borehole.

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