Hydraulically powered centralizer device for borehole and method

1. A centralizing device configured to centralize/decentralize an associated tool in a well, the centralizing device comprising:

a body that extends along a longitudinal axis, the body having a bore that extends from one end to another end of the body;

a first piston shaped as a cylinder and provided around a central portion of the body;

a second piston shaped as a cylinder and provided around the central portion of the body;

a bridge provided around the central portion of the body, between the first and second pistons; and

a pair of arms, each arm being attached with one end to a corresponding one of the first and second pistons and with another end to each other,

wherein the second piston, the bridge, and the central portion of the body define a first sealed chamber containing a gas that exerts a pressure tending to separate the first piston and the second piston.

2. The centralizing device of claim 1 , wherein the first piston, the bridge, and the central portion of the body form a second sealed chamber.

3. The centralizing device of claim 2 , wherein the gas contained within the first sealed chamber comprises air at a given pressure.

4. The centralizing device of claim 3 , wherein the centralizing device is configured such that a hydrostatic pressure inside the well tends to move the first piston and the second piston towards each other so that the pair of arms fold and a joint of the arms moves radially away from the longitudinal axis.

5. The centralizing device of claim 1 , wherein the gas contained within the first sealed chamber comprises air at a given pressure.

6. The centralizing device of claim 5 , wherein the centralizing device is configured such that a hydrostatic pressure inside the well tends to move the first piston and the second piston towards each other so that the pair of arms fold and a joint of the arms moves radially away from the longitudinal axis.

7. The centralizing device of claim 1 , wherein the second piston forms with the body a variable gap, that communicates with an ambient environment within the well.

8. The centralizing device of claim 7 , wherein the second piston is configured to move along the longitudinal axis, under a hydrostatic pressure formed in the variable gap, to reduce a size of the first sealed chamber.

9. The centralizing device of claim 1 , wherein at least one of the one end or the another end of the body is configured to be attached to a perforating gun.

10. The centralizing device of claim 1 , further comprising:

additional pairs of arms, each pair connected between the first and second pistons.

11. The centralizing device of claim 10 , wherein the pair of arms and the additional pairs of arms are symmetrically distributed around the body to centralize the tool relative to a central axis of the well.

12. The centralizing device of claim 10 , wherein the pair of arms and the additional pairs of arms are asymmetrically distributed around the body to decentralize the tool relative to a central axis of the well.

13. The centralizing device of claim 1 , further comprising:

a roller attached to a joint of the pair of arms.

14. The centralizing device of claim 1 , further comprising:

a weight attached to the pair of arms to obtain a desired orientation of the body relative to gravity.