Expander for expanding a tubular element

1. An expander for radially expanding a tubular element by axial movement of the expander through the tubular element, the expander comprising an expander member having a front part of a first cross-sectional size, a rear part of a second cross-sectional size larger than the first cross-sectional size, and an intermediate part arranged between said front part and rear part and having a cross-sectional size varying between said first and second cross-sectional sizes, wherein the expander member is provided with fluid supply means for supplying pressurized fluid to the inner surface of the tubular element at a location opposite said intermediate part when the expander member is arranged in the tubular element.

2. The expander of claim 1 , wherein the expander is arranged to be moved through the tubular element by the action of fluid pressure of a body of fluid acting on the expander member, and wherein the fluid supply means includes a fluid passage providing fluid communication between said body of fluid and the inner surface of the tubular element at said location.

3. The expander of claim 1 , wherein said front part of the expander member is provided with sealing means arranged to seal the front part relative to the inner surface of the tubular element.

4. The expander of claim 3 , wherein the expander member includes different elements movable relative to each other between a retracted position in which said rear part has a cross-sectional size smaller than said second cross-sectional size and an expanded position in which the rear part has said second cross-sectional size.

5. The expander of claim 3 , wherein the sealing means includes an annular seal of outer diameter substantially equal to the inner diameter of the tubular element before expansion thereof.

6. The expander of claim 3 , wherein the sealing means is one of a group consisting of ceramic seal, a labyrinth seal and a hard metal seal.

7. The expander of claim 1 , wherein the expander member is cone-shaped.

8. The expander of claim 1 , wherein the expander member is provided with rollers arranged to roll along the inner surface of the tubular element during expansion thereof.

9. The expander of claim 1 , wherein the tubular element is one of a wellbore tube and a surface pipe.

10. A method of radially expanding a tubular element, comprising

a) moving an expander in axial direction through the tubular element, the expander including an expander member having a front part of a first cross-sectional size, a rear part of a second cross-sectional size larger than the first cross-sectional size, and an intermediate part arranged between said front part and rear part and having a cross-sectional size varying between said first and second cross-sectional sizes; and

b) simultaneously with step a), supplying pressurized fluid to the inner surface of the tubular element at a location opposite said intermediate part.

11. The method of claim 10 , wherein in step a) the expander is moved through the tubular element by the action of fluid pressure of a body of fluid acting on the expander member, and wherein in step b) said pressurized fluid is supplied to the inner surface of the tubular element via a fluid passage formed in the expander member, said fluid passage providing fluid communication between said body of fluid and said inner surface of the tubular element.

12. The expander of claim 2 , wherein said front part of the expander member is provided with sealing means arranged to seal the front part relative to the inner surface of the tubular element.

13. The expander of claim 4 , wherein the sealing means includes an annular seal of outer diameter substantially equal to the inner diameter of the tubular element before expansion thereof.

14. The expander of claim 4 , wherein the sealing means is one of a group consisting of ceramic seal, a labyrinth seal and a hard metal seal.

15. The expander of claim 5 , wherein the sealing means is one of a group consisting of ceramic seal, a labyrinth seal and a hard metal seal.