Downhole anti-rotation tool

A tool to prevent rotation of a downhole tool suspended in a wellbore casing comprising:

• a tubular housing having a wall for engaging the casing and having at least one end for connection to the downhole tool;
• a jaw having a radial tip and which is rotatable from a point on the housing opposing the casing engaging wall for varying the effective diameter of the tool, and
• a hinge, acting between the jaw and the housing so as to permit the jaw to rotate between a first outwardly extending casing-engaging position wherein the radial tip is positioned outwardly from the housing to increase the tool's effective diameter so that the radial tip engages the casing and the housing wall engages the casing for arresting tool rotation and a second compressed position wherein the jaw is temporarily compressed towards the housing for minimizing the tool's effective diameter and permitting movement within the casing, the hinge connected to the housing so as to permit sufficient movement of the jaw relative to the hinge to permit the jaw to engage the housing and transfer substantially all of the force directly to the housing, minimizing the force on the hinge, the hinge having
• a linearly extending flexible torsional member connected rigidly to the housing at a first end and connected to the jaw at a second end so as to twist the member into torsion upon rotation of the second end relative to the first;
• and
• a tubular conduit having first and second ends extending along an edge of the jaw for accepting the torsional member.

An improvement to a tool used to prevent rotation of a downhole tool suspended in a wellbore casing, the tool having a housing and at least one jaw having an edge which is pivotable at a hinge on the housing, the hinge having first and second ends pivotally connected to the housing, the improvement comprising:

• a torsional member having first and second ends;
• and
• a first holder for pinning the first end of the torsional member to the housing;
• and
• a second holder pivotable with the jaw and for pinning the second end of the torsional member to the jaw so that when the jaw pivots towards the housing, the torsional member is twisted for biasing the jaw outwardly.