Downhole packer

1. A downhole packer comprising:

a first locking member positioned at least partially around an outer surface of an oilfield tubular, the first locking member comprising an inner surface that engages the outer surface of the tubular, and a tapered outer surface;

a drive ring positioned at least partially around the first locking member and comprising a reverse-tapered inner surface that engages the tapered outer surface of the first locking member;

a first cap movably coupled with the drive ring, disposed at least partially around the first locking member, and axially-engaging the first locking member, wherein moving at least one of the first cap and the drive ring toward the other causes the drive ring to apply a radially-inward force on the first locking member, causing the first locking member to be secured to the tubular; and

a sealing element configured to be disposed at least partially around the tubular and held in position at least axially with respect thereto by the first locking member engaging the tubular, wherein the sealing element is configured to expand radially-outward in response to application of an axially-directed, compressive force,

wherein the inner surface of the first locking member comprises a plurality of teeth, and

wherein relative rotation between the drive ring and the first cap causes the first cap and the drive ring to move closer together.

2. The downhole packer of claim 1 , wherein the drive ring is disposed axially-intermediate of the sealing element and the first cap.

3. The downhole packer of claim 1 , wherein:

an inner surface of the first cap has a plurality of threads formed thereon that engage a plurality of threads formed on an outer surface of the drive ring;

the first locking member is positioned at least partially axially-between the first cap and the drive ring; and

the first locking member is positioned at least partially radially-between the outer surface of the tubular and the drive ring, at least partially radially-between the outer surface of the tubular and the first cap, or both.

4. A downhole packer comprising:

a first locking member positioned at least partially around an outer surface of an oilfield tubular, the first locking member comprising an inner surface that engages the outer surface of the tubular, and a tapered outer surface;

a drive ring positioned at least partially around the first locking member and comprising a reverse-tapered inner surface that engages the tapered outer surface of the first locking member;

a first cap movably coupled with the drive ring, disposed at least partially around the first locking member, and axially-engaging the first locking member, wherein moving at least one of the first cap and the drive ring toward the other causes the drive ring to apply a radially-inward force on the first locking member, causing the first locking member to be secured to the tubular; and

a sealing element configured to be disposed at least partially around the tubular and held in position at least axially with respect thereto by the first locking member engaging the tubular, wherein the sealing element is configured to expand radially-outward in response to application of an axially-directed, compressive force,

wherein the inner surface of the first locking member comprises a plurality of teeth, and wherein the plurality of teeth comprise at least two of: left-hand threads, right-hand threads, and axially-extending threads.

5. The downhole packer of claim 4 , further comprising:

a piston positioned at least partially around the outer surface of the tubular and adjacent to the sealing element, wherein the piston is movable in at least one axial direction, to apply the compressive force to the sealing element; and

a sleeve positioned a least partially around an outer surface of the piston, wherein a chamber is defined between the outer surface of the tubular and the piston, between the outer surface of the tubular and the sleeve, or a combination thereof, and wherein the chamber is in fluid communication with an interior of the tubular through an opening in the tubular.

6. The downhole packer of claim 5 , further comprising a ratchet ring positioned at least partially around the outer surface of the piston, wherein an inner surface of the ratchet ring has a plurality of teeth formed thereon that are configured to engage a corresponding plurality of teeth formed on the outer surface of the piston, thereby allowing the piston to move in a first axial direction with respect to the tubular while preventing the piston from moving in a second, opposing axial direction with respect to the tubular.

7. The downhole packer of claim 6 , wherein the ratchet ring is positioned within a recess or pocket formed in the sleeve.

8. The downhole packer of claim 5 , further comprising a second locking member positioned at least partially around the outer surface of the tubular, wherein an inner surface of the second locking member has a plurality of teeth formed thereon that contact the outer surface of the tubular, and wherein an outer surface of the second locking member is sloped at a non-zero angle with respect to the outer surface of the tubular.

9. The downhole packer of claim 8 , wherein an inner surface of the sleeve is sloped at a non-zero angle with respect to the outer surface of the tubular, and wherein the inner surface of the sleeve is configured to contact the outer surface of the second locking member.

10. The downhole packer of claim 8 , further comprising a second cap positioned at least partially around the outer surface of the tubular, wherein an inner surface of the second cap has a plurality of threads formed thereon that are configured to engage a plurality of threads formed on an outer surface of the sleeve, wherein the second locking member is positioned at least partially axially-between the sleeve and the second cap, and wherein the second locking member is positioned at least partially radially-between the outer surface of the tubular and the sleeve, at least partially radially-between the outer surface of the tubular and the second cap, or both.

11. The downhole packer of claim 10 , wherein relative rotation between the sleeve and the second cap causes the second locking member to apply a radially-inward gripping force against the outer surface of the tubular.

12. A method for assembling a downhole packer, comprising:

positioning a first cap, a first locking member, a drive ring, and a sealing element around an outer surface of a tubular, wherein the first locking member is positioned at least partially axially-between the first cap and the drive ring, and wherein the first locking member is positioned at least partially radially-between the outer surface of the tubular and the drive ring, at least partially radially-between the outer surface of the tubular and the first cap, or both; and

moving the first cap and the drive ring toward one another, thereby causing the first locking member to apply a radially-inward force against the outer surface of the tubular to secure the packer in place on the tubular,

wherein an inner surface of the first cap has a plurality of threads formed thereon that are configured to engage a corresponding plurality of threads on an outer surface of the drive ring, and wherein moving the first cap and the drive ring toward one another comprises rotating the first cap with respect to the drive ring.

13. A method for assembling a downhole packer, comprising:

positioning a first cap, a first locking member, a drive ring, and a sealing element around an outer surface of a tubular, wherein the first locking member is positioned at least partially axially-between the first cap and the drive ring, and wherein the first locking member is positioned at least partially radially-between the outer surface of the tubular and the drive ring, at least partially radially-between the outer surface of the tubular and the first cap, or both;

moving the first cap and the drive ring toward one another, thereby causing the first locking member to apply a radially-inward force against the outer surface of the tubular to secure the packer in place on the tubular; and

positioning a piston, a sleeve, a second locking member, and a second cap around the outer surface of the tubular, wherein the piston is positioned adjacent to the sealing element, wherein at least a portion of the sleeve is positioned radially-outward from the piston, wherein an inner surface of the second cap has a plurality of threads formed therein that are configured to engage a corresponding plurality of threads on an outer surface of the sleeve, and wherein an inner surface of the sleeve and an outer surface of the second locking member are sloped at non-zero angles with respect to the outer surface of the tubular and configured to contact one another.

14. The method of claim 13 , further comprising inserting a ratchet ring into a pocket or recess formed in the sleeve, wherein an inner surface of the ratchet ring has a plurality of teeth formed thereon that are configured to engage a corresponding plurality of teeth formed on an outer surface of the piston, thereby allowing the piston to move in a first axial direction with respect to the tubular while preventing the piston from moving in a second, opposing axial direction with respect to the tubular.

15. The method of claim 13 , further comprising:

selecting a location for the packer on the tubular between ends of the tubular;

forming one or more pressure-communication openings through the tubular at the location; and

aligning a chamber with the one or more pressure-communication openings, wherein the chamber is defined radially between the sleeve and the tubular and at least partially defined by the piston.

16. A method for actuating a packer in a wellbore, comprising:

running the packer into the wellbore, wherein the packer comprises:

a first locking member positioned at least partially around an outer surface of a tubular, wherein an inner surface of the first locking member has a plurality of teeth formed thereon that contact the outer surface of the tubular, and wherein an outer surface of the first locking member is sloped at a non-zero angle with respect to the outer surface of the tubular;

a drive ring positioned at least partially around the outer surface of the tubular, wherein an inner surface of the drive ring is sloped at a non-zero angle with respect to the outer surface of the tubular, and wherein the inner surface of the drive ring is configured to contact the outer surface of the first locking member;

a first cap positioned at least partially around the outer surface of the tubular, wherein an inner surface of the first cap has a plurality of threads formed thereon that are configured to engage a plurality of threads formed on an outer surface of the drive ring;

a sealing element positioned at least partially around the outer surface of the tubular and adjacent to the drive ring;

a piston positioned at least partially around the outer surface of the tubular and adjacent to the sealing element; and

a sleeve positioned a least partially around an outer surface of the piston, wherein a chamber is defined between the outer surface of the tubular and the piston, between the outer surface of the tubular and the sleeve, or a combination thereof, and wherein the chamber is in fluid communication with an interior of the tubular through an opening in the tubular; and

causing a pressure of a fluid in the tubular and in the chamber to increase, wherein, in response to the increased pressure, the piston moves axially toward the sealing element, causing the sealing element to actuate radially-outward from a collapsed state to an expanded state.

17. The method of claim 16 , wherein the first locking member is positioned at least partially axially-between the first cap and the drive ring, and wherein the first locking member is positioned at least partially radially-between the outer surface of the tubular and the drive ring, at least partially radially-between the outer surface of the tubular and the first cap, or both.