Downhole anchoring device

Abstract

There is disclosed an apparatus for axially anchoring a tool downhole in a well casing, the apparatus comprising: an anchor configured to be disposed in, and actuatably and rotatably engaged with, the casing; and a rotatable tool being configured to be disposed within the casing; whereby the anchor, when rotatably engaged with the casing, prevents movement of the rotatable tool in the axial direction A whilst allowing for rotation of the tool about the axial direction. A corresponding method of anchoring a tool downhole is also disclosed.

1 . An apparatus for axially anchoring a tool downhole in a well casing, the apparatus comprising:
 an anchor configured to be disposed in, and actuatably and rotatably engaged with, the casing; and   a rotatable tool being configured to be disposed within the casing;   whereby the anchor, when rotatably engaged with the casing, prevents movement of the rotatable tool in the axial direction whilst allowing for rotation of the tool about the axial direction.   
     
     
         2 . The apparatus of  claim 1 , wherein the rotatable tool is connected below the anchor in the axial direction. 
     
     
         3 . The apparatus of  claim 1  or  2 , wherein the anchor and the rotatable tool are rotationally locked to one another. 
     
     
         4 . The apparatus of any preceding claim, wherein the anchor is arranged to be actuated into rotatable engagement with the casing by a fluid, preferably drilling mud. 
     
     
         5 . The apparatus of any preceding claim, wherein the anchor comprises a substantially hollow body. 
     
     
         6 . The apparatus of any preceding claim, wherein the anchor comprises a plurality of extendable casing engagement blocks. 
     
     
         7 . The apparatus of  claim 6 , wherein the blocks are actuatable from a retracted position in which the blocks are substantially housed within the body to an actuated position in which the blocks extend radially from the body. 
     
     
         8 . The apparatus of  claim 6  or  7 , wherein the plurality of blocks are disposed circumferentially around the anchor in at least one plane perpendicular to the axial direction, each plane comprising at least two blocks. 
     
     
         9 . The apparatus of any of  claims 6  to  8 , wherein the plurality of blocks are disposed in more than one plane perpendicular to the axial direction, and preferably in at least two planes perpendicular to the axial direction. 
     
     
         10 . The apparatus of any of  claims 7  to  9 , wherein the blocks are biased towards the retracted position. 
     
     
         11 . The apparatus of any of  claims 7  to  10 , wherein the body comprises at least one opening through which the plurality of blocks extends through in the actuated position. 
     
     
         12 . The apparatus of  claim 11 , wherein a plurality of openings is provided, and wherein there is preferably one opening for every block of the plurality of blocks. 
     
     
         13 . The apparatus of any of  claims 6  to  12 , wherein the blocks comprise at least one engagement wheel rotatably mounted thereto in a plane perpendicular to the axial direction, the at least one wheel being configured to rotatably engage with the inner surface of the casing. 
     
     
         14 . The apparatus of  claim 13 , wherein each of the at least one wheels on each of the plurality of blocks has a knife-edge circumference arranged to cut into the surface of the casing. 
     
     
         15 . The apparatus of  claim 13  or  14 , wherein each of the at least one wheels on each of the plurality of blocks has a circular outer circumference. 
     
     
         16 . The apparatus of  claims 13  to  15 , wherein each of the wheels is formed of high carbon steel or tungsten carbide. 
     
     
         17 . The apparatus of any of  claims 13  to  16 , wherein the engagement of the wheels with the casing forms a groove in the casing, whereby the wheel may freely rotate against the casing in a plane of the groove whilst preventing movement of the wheels in the axial direction. 
     
     
         18 . The apparatus of any of  claims 13  to  17 , wherein a wheel on each of the plurality of blocks is axially aligned with at least one other wheel on another block. 
     
     
         19 . The apparatus of any preceding claim, wherein the rotatable tool is a casing cutter for cutting through the casing. 
     
     
         20 . The apparatus of  claim 19 , wherein the casing cutter comprises a plurality of blades, the blades being hydraulically actuatable into contact with the casing. 
     
     
         21 . The apparatus of  claim 20 , wherein the blades comprise high carbon steel, or tungsten carbide. 
     
     
         22 . A drillstring comprising the apparatus of any preceding claim, wherein the drillstring extends downwardly from a rig or vessel, and wherein rotation of the drillstring drives the apparatus into simultaneous rotation. 
     
     
         23 . The drillstring of  claim 22 , configured to allow fluid to pass down therethrough to engage the apparatus. 
     
     
         24 . The drillstring of  claim 22  or  23 , further comprising a length compensating device (LCD) disposed above the apparatus in the axial direction. 
     
     
         25 . The drillstring of  claim 24 , wherein the LCD is a bumper sub. 
     
     
         26 . The drillstring of  claim 24  or  25 , further comprising a controller associated with the LCD, the controller being configured to alter the length of the LCD. 
     
     
         27 . The drillstring of any of  claims 22  to  26 , wherein the drillstring is connected to a surface heave compensator disposed at the rig or vessel. 
     
     
         28 . A method of anchoring a tool downhole within a casing of a subsea oil well comprising the steps of:
 providing:
 a drillstring extending downwardly from a rig or vessel; 
 an actuatable anchor rotatably mounted on the drillstring; and 
 a rotatable tool disposed on the drillstring; 
   locating the tool in a desired position downhole within the casing;   actuating the anchor into rotatable engagement with the casing; and   actuating the tool;   whereby the anchor prevents axial movement of the actuated tool.   
     
     
         29 . The method as claimed in  claim 28 , wherein the tool is a casing cutter. 
     
     
         30 . The method as claimed in  claim 29 , further comprising extending the casing cutter into rotational contact with the casing whilst allowing the casing cutter to rotate about the axial direction so as to cut through a depth of the casing. 
     
     
         31 . A method of cutting a casing of a subsea oil well comprising the steps of:
 providing the drillstring of any of  claims 22  to  27 ;   lowering the drillstring from the rig or vessel to align the anchor and the casing cutter in a desired position within the casing; and   passing a fluid down the drillstring to activate the anchor and the casing cutter, wherein,   the fluid actuates the anchor into rotatable engagement with the casing and the casing cutter into contact with the casing such that the anchor prevents movement of the casing cutter in the axial direction whilst allowing the casing cutter to rotate about the axial direction to cut through a depth of the casing in a radial plane perpendicular to the axial direction.   
     
     
         32 . The method of  claim 31 , further comprising the use of a length compensation device controlled by a controller. 
     
     
         33 . An apparatus for cutting a casing of a subsea oil well, the apparatus comprising:
 a drillstring extending downwardly from a rig or vessel;   an anchor rotatably mounted on the drillstring and configured to be disposed in, and rotatably and actuatably engaged with, the casing; and   a rotatable casing cutter disposed on the drillstring and configured to be disposed within and cut through the casing;   
       whereby the anchor, when rotatably engaged with the casing, prevents movement of the casing cutter in the axial direction whilst allowing for rotation of the casing cutter about the axial direction.