Patent Application
20110155465
The invention relates to tools used in underreaming well bores, providing a underreaming tool with radially extendable and retractable cutting elements.
Underreaming of a well bore is a means of expanding a zone in a well bore to a greater diameter by cutting material away from the side of the well bore. Because the well bore is to be expanded in diameter, it is necessary to provide a tool that can run into the well bore in a “closed” position, then allow the cutting elements of the tool to extend radially outward until the desired bore diameter is reached.
An example of such a tool is described in U.S. Pat. No. 4,282,942 to Longmore. That tool utilizes reverse circulation pressure to drive a cam to pivotally extend the cutting elements. Once the underreaming operation is complete, the reverse circulation pressure is removed and the cutting elements are allowed to collapse back to the tool body by gravity.
Another type of underreamer is described in U.S. Pat. No. 5,853,054 to MaGarian, et al. That tool utilizes hydraulic pistons to pivotally extend and retract the cutting elements of the tool. However, it also anticipates that power to these pistons may be lost, and provides for biasing springs to retract the cutting elements if power is lost to the retracting piston.
While useful, underreaming tools create a risk of having the tool stuck downhole if the cutting elements do not sufficiently or fully retract. Because underreamers are used to selectively increase the diameter of well bores, the nature of the operation will create a shoulder above the underreamed zone where the well bore narrows to its original diameter. Conversely, if the underreaming operation is performed below casing, the casing itself will present a narrow diameter through which the tool must fit to be retrieved from the well bore. Thus, an underreamer that fails to fully retract may become stuck, requiring time consuming efforts (and therefore expensive) efforts to fish it out of the well bore, or to grind through it.
Other reliability problems can occur with current underreamers. For example, the cutting elements may fail to fully extend, preventing the underreaming operation from proceeding to the full desired diameter. Such a circumstance may require retrieving the underreamer from the well bore, repairing or replacing it, and running into the well bore again to complete the underreaming operation. Such instances are extremely undesirable due to the lost time and expense of running in and out of the well bore.
Accordingly, it is an object of the invention to provide an underreamer with improved reliability. Further objects of the invention include further improving reliability by providing a positive indication at the surface when the cutting elements have been fully extended, and again when they have been fully retracted.
The invention is an underreamer comprising a cam-driven mechanism to extend and retract the cutting elements. When activated, the cam applies a radial force to the cutting elements essentially perpendicular to the longitudinal axis of the tool body. Thus, the cutting elements do not pivot relative to the tool body as they extend and retract, but move radially essentially perpendicularly to the longitudinal axis of the tool.
The invention further provides a mechanism for selectively setting the cam in position to extend the cutting elements, and for selectively setting the cam in position to retract the cutting elements after underreaming operations are complete. This mechanism provides two different drop ball seats, the lower one of smaller diameter than the upper one. (As used herein, “upper” is intended to mean only “closer to the surface,” because the tool string may not be vertical.)
When it is desired to set the cutting elements in the extended position, a first drop ball of a diameter small enough to pass through the upper drop ball seat is dropped through the tool string. The first drop ball travels though the tool body, past the upper drop ball seat, and seats in the lower drop ball seat, interrupting fluid flow through the tool body. Hydraulic pressure can then be used to shear a first set of shear screws. When the first set of shear screws shear, the hydraulic pressure shifts the cam and lower ball seat downward, moving the cutting elements into their extended position. Once the cutting elements are fully extended, a lower flow diverter opens to allow fluid flow around the lower ball seat. The resulting reduction in hydraulic pressure provides a positive indication at the surface that the cutting elements are fully extended.
Similarly, when the underreaming operation is complete and it is desired to set the cutting elements in the retracted position, a second drop ball of a diameter sufficient to seat in the upper drop ball seat is dropped through the tool string. The second drop ball seats in the upper drop ball seat, again interrupting fluid flow through the tool body. Hydraulic pressure can then be used to shear a second set of shear screws. When the second set of shear screws shear, the hydraulic pressure shifts the cam and upper ball seat downward, moving the cutting elements into their retracted position. Once the cutting elements are fully retracted, an upper flow diverter opens to allow fluid flow around the upper ball seat. The resulting reduction in hydraulic pressure provides a positive indication at the surface that the cutting elements are fully retracted.
In a preferred embodiment, upper and lower ratcheting followers are provided, so that as each shift of the cam is performed, the ratcheting followers prevent reverse shifting of the cam.
Referring to
Underreamer 10 comprises a tool body 12, cam 14, cutting elements 16, upper ball seat 18, and lower ball seat 20. Cutting elements 16 are aligned with openings 22 in tool body 12 (see also tool body 512 with openings 522 of
A more detailed view of this activation timing is shown in
Similarly,
Referring again to
Once the underreamer 10 is positioned in a well bore (not shown) the cutting elements 16 must be opened to allow underreaming to begin. Referring more particularly to
Those of skill in the art will recognize that, while the use of ball seats and drop balls is embodied in the preferred embodiment of the invention, any seat capable of engaging a plugging device may be used in place of the ball seats described herein, and other plugging devices known to those of skill in the art may be used in place of drop balls.
The increasing hydraulic pressure forces shears first lower shear screws 28, allowing piston 19 to shift downward. This action causes first upper shear screws 62 to shear and releases lower ball seat 20, lower seal sleeve 30, cam 14, and upper ball seat 18 to travel downward until lower seal sleeve 30 engages lower shoulder 32. This displacement aligns the tapers 24 of cam 14 with cutting elements 16 so that cutting elements 16 are extended from the tool body 12. This motion also moves upper retaining ring 66 into contact with upper shoulder 68.
During the course of the opening operation, upper ratchet 94 travels downward along upper ratchet platen 96, providing a positive locking force prevent upward movement of piston 19.
Referring to
As part of the setting process, lower ratchet 42 (see
When underreaming is complete, it is necessary to retract cutting elements 16 to allow retrieval of underreamer 10. Referring to
Fluid pressure shears second upper shear screws 70, upper ball seat 18 shift downward, allowing first upper locking balls 48 drop into upper ball seat grooves 52, locking upper ball seat 18 and upper sealing sleeve 50 together to close first gap 78. Continued downward movement of upper ball seat 18 forces first upper locking balls 48 outward by the curvature of upper ball seat grooves 52, releasing the lock between upper ball seat 18 and upper sealing sleeve 50.
Cam 14 can now move downward, shearing lower shear screws 54. The shearing of second lower shear screws 54 allows lower inner sleeve 56 (and therefore cam 14 and upper ball seat 18) to move relative to lower sealing sleeve 30 and lower ball seat 20. The down-ward shift of cam 14 draws cutting elements 16 inward to a fully retracted position.
Third upper shear screws 76 also shear in this action, releasing seal bushing 64 into annulus 92 to prevent fluid flow through annulus 92 when circulation is reestablished. Seal bushing 92 is allowed to “float” to equalize pressures above and below it.
Downward travel continues until lower retaining ring 67 engages inner shoulder 74. Hydraulic pressure shears fourth upper shear screws 77, allowing a continued downward shift of upper ball seat 18 and spacer 51. As reflected in
Cam 14 is pushed downward until further movement is stopped by contact with intermediate shoulder 58.
Upper ball seat 18 and spacer 51 shift downward, closing second gap 80, until the lower end of spacer 51 shoulders on torn end 81 of bottom push tube 83. (See
Referring to
Referring to
The above examples are included for demonstration purposes only and not as limitations on the scope of the invention. Other variations in the construction of the invention may be made without departing from the spirit of the invention, and those of skill in the art will recognize that these descriptions are provide by way of example only.
