Self-anchoring device with force amplification

1. A downhole tool comprising a grip assembly for contacting a well formation, the grip assembly comprising:

a gripper body;

a centralizer that is attached to and radially expandable with respect to the gripper body and that has a geometry which is lockable by a locking device;

a force amplifier in force transmitting relation with the centralizer, wherein the force amplifier transfers a force in a first direction to a much larger force in a second direction when the centralizer is locked by the locking device;

wherein the force amplifier comprises a saddle having a surface for contacting the well formation in area contact;

wherein the grip assembly has a power stroke and a return stroke, and wherein the saddle remains in contact with the well formation during both the power stroke and the return stroke; and

wherein the saddle has a first coefficient of friction with the well formation during the power stroke and a second coefficient of friction with the well formation during the return stroke, and wherein the first coefficient of friction is higher than the second coefficient of friction.

2. The downhole tool of claim 1 , wherein the centralizer comprises a force transmission member in force transmitting relation to an inclined surface on the saddle to form said force transmitting relation between the force amplifier and said centralizer, such that an interaction between the force transmission member and the inclined surface on the saddle causes said force transfer by the force amplifier.

3. The downhole tool of claim 2 , wherein said first direction is an axial direction with respect to the tool body, and wherein said second direction is a radial direction with respect to the tool body.

4. The downhole tool of claim 3 , wherein said force in said axial direction is a force applied to the grip assembly which causes the remainder of the tool to move in an opposite direction from said axial direction.

5. The downhole tool of claim 1 , wherein the saddle is anchored to the well formation during the power stroke, and the saddle is moveable relative to the well formation during the return stroke, and wherein the centralizer centralizes the downhole tool with respect to the well formation during the return stroke.

6. The downhole tool of claim 1 , wherein the force amplifier is a mechanical force amplifier.

7. The downhole tool of claim 1 , wherein the force amplifier is a hydraulic force amplifier.

8. The downhole tool of claim 1 , wherein the hydraulic force amplifier comprises a first hydraulic cylinder in fluid communication with a second hydraulic cylinder, and wherein the first hydraulic cylinder has a higher fluid contact area than the second hydraulic cylinder.

9. The downhole tool of claim 1 , wherein the centralizer comprises a plurality of linkages.

10. The downhole tool of claim 1 , wherein the centralizer comprises a plurality of linkages, and wherein each linkage comprises a force receiving member which interacts with a force transmitting member on the gripper body to create said radial expansion of the centralizer with respect to the gripper body.

11. The downhole tool of claim 1 , wherein said force receiving member on the linkages is a wedge and wherein said force transmitting member on the gripper body is a wheel.

12. The downhole tool of claim 1 , wherein the downhole tool is a tractor.

13. The downhole tool of claim 12 , wherein the downhole tool is a tractor that is bi-directionally operable.

14. The downhole tool of claim 12 , wherein the well formation is an open hole formation.

15. The downhole tool of claim 1 , wherein the downhole tool is a mechanical services tool capable of performing an mechanical services operation.

16. The downhole tool of claim 1 , wherein said surface of said saddle for contacting the well formation in area contact is harder than a remainder of the saddle.

17. A downhole tool comprising a grip assembly for contacting a well formation, the grip assembly comprising:

a gripper body;

a centralizer that is attached to and radially expandable with respect to the gripper body and that has a geometry which is lockable by a locking device;

a force amplifier in force transmitting relation with the centralizer, wherein the force amplifier transfers a force in a first direction to a much larger force in a second direction when the centralizer is locked by the locking device;

wherein the force amplifier comprises a saddle having a surface for contacting the well formation;

wherein the grip assembly has a power stroke and a return stroke; and

wherein the saddle has a first coefficient of friction with the well formation during the power stroke and a second coefficient of friction with the well formation during the return stroke, and wherein the first coefficient of friction is higher than the second coefficient of friction.