Downhole anchor mechanism
A downhole anchor mechanism ( 110 ) which can be set on at least two successive standard diameters of casing ( 232 ). The tool body has a recess into which a split cone ( 70 ) is located. The increased thickness of the split cone ( 70 ) provides for a greater thickness of slip ( 90 ), giving increased radial travel of the slips 90 when moved axially over the split cone ( 70 ). The cone ( 70 ) and slips ( 90 ) are profiled to provide two ramps/slopes for increased structural integrity and a greater ramp angle to reduce the axial travel of the slips to achieve the increased radial travel. The downhole anchor mechanism ( 110 ) provides anchoring of a work string on two standard diameters of casing in a single trip in a wellbore.
1. An anchor mechanism for gripping wellbore casing, comprising:
a tool body being tubular with a central bore between an inlet and a first outlet, the inlet and first outlet being adapted for connection in a work string to be run into the casing;
a recess provided in and around an outer surface of the tool body;
a cone arranged in the recess, the cone having an outer surface including a first profile, the first profile having at least one ramp;
a plurality of selectively operable slips, each slip having an outer surface configured to grip an inner surface of the casing and an inner surface including a second profile, the second profiling mating with the first profile in a first configuration; and
piston means operable to move the slips over the cone between the first configuration wherein the slips are located within the recess, a second configuration wherein the outer surface of the slips contacts the inner surface of casing of a first standard diameter;
and characterised in that:
the cone is a split cone, of two part construction, as the cone is split longitudinally to create two halves; and
the piston means is operable to move the slips over the split cone to a third configuration wherein the outer surface of the slips contacts the inner surface of casing of a second standard diameter;
wherein the first standard diameter and the second standard diameter are at least two successive different standard diameters of wellbore casing, and the standard diameters for casing are selected from a group comprising: 5″, 5½″, 6″, 6⅝″ 7″, 7⅝″, 8⅝″, 9⅝″, 10¾″, 11¾″, 13⅜″, 14″, 16″, 18⅝″ and 20″.
2. An anchor mechanism according to claim 1 wherein the first profile includes two spaced apart ramps.
3. An anchor mechanism according to claim 2 wherein a first ramp is shorter than a second ramp and wherein the second ramp is arranged towards a base of the split cone.
4. An anchor mechanism according to claim 3 wherein the first ramp ends at a first plateau, the first plateau having a surface parallel to a longitudinal axis through the tool body.
5. An anchor mechanism according to claim 4 wherein the second ramp begins with a second plateau, the second plateau having a surface parallel to a longitudinal axis through the tool body.
6. An anchor mechanism according to claim 1 wherein the tool body is rotatable relative to the slips.
7. An anchor mechanism according to claim 6 wherein a bearing is located between a base of the split cone and a side wall of the recess.
8. An anchor mechanism according to claim 1 wherein the piston means comprises a sleeve axially moveable relative to the tool body and arranged to act on a face of each slip.
9. An anchor mechanism according to claim 8 wherein the piston means is mechanically or hydraulically operated.
10. An anchor mechanism according to claim 9 wherein the piston means is hydraulically operated by action of fluid from the central bore.
11. An anchor mechanism according to claim 8 wherein the sleeve is configured to move in response to fluid pressure acting on the sleeve or at least part of the sleeve.
12. An anchor mechanism according to claim 8 wherein a first end of each slip is located under the sleeve.
13. An anchor mechanism according to claim 1 wherein the anchor mechanism includes biasing means to hold the slips in the first configuration.
14. An anchor mechanism according to claim 13 wherein the biasing means is a spring arranged to act against the piston.
15. A method of using a downhole anchor in a wellbore, comprising the steps:
(a) mounting an anchor mechanism on a work string, the anchor mechanism comprising a plurality of operable slips, each slip having an outer surface configured to grip an inner surface of casing;
(b) running the work string in the wellbore and locating the anchor mechanism in casing of a first standard diameter;
(c) setting the slips to anchor the anchor mechanism to an inner surface of the casing of a first standard diameter;
(d) performing a task in the wellbore;
(e) unsetting the slips to release the anchor mechanism from the inner surface of the casing of a first standard diameter; and
characterised in that, the method comprises the additional steps of:
(f) moving the work string in the wellbore and locating the anchor mechanism in casing of a second standard diameter; and
(g) setting the slips to anchor the anchor mechanism to an inner surface of the casing of a second standard diameter;
wherein the first standard diameter and the second standard diameter are at least two successive different standard diameters of wellbore casing being selected from a group comprising 5″, 5½″, 6″, 6⅝″ 7″, 7⅝″, 8⅝″, 9⅝″, 10¾″, 11¾″, 13⅜″, 14″, 16″, 18⅝″ and 20″.
16. A method according to claim 15 wherein the first and second standard diameters are 9⅝″ and 10¾″.
17. An anchor mechanism for gripping wellbore casing, comprising:
a tool body being tubular with a central bore between an inlet and a first outlet, the inlet and first outlet being adapted for connection in a work string to be run into the casing;
a recess provided in and around an outer surface of the tool body;
a split cone arranged in the recess, the split cone having an outer surface including a first profile, the first profile having at least one ramp;
a plurality of selectively operable slips, each slip having an outer surface configured to grip an inner surface of the casing and an inner surface including a second profile, the second profiling mating with the first profile in a first configuration; and
piston means operable to move the slips over the split cone between the first configuration wherein the slips are located within the recess, a second configuration wherein the outer surface of the slips contacts the inner surface of casing of a first standard diameter and a third configuration wherein the outer surface of the slip contacts the inner surface of casing of a second standard diameter:
wherein the first standard diameter and the second standard diameter are at least two successive different standard diameters of wellbore casing; and
the tool body is rotatable relative to the slips via a bearing located between a base of the split cone and a side wall of the recess.