Reducing swab pressure generated behind a well liner expansion cone

1. A method of expanding at least an upper section of a well liner configured within a lower section of a previously installed liner, the method comprising:

pulling an expansion mandrel up through the well liner, in an area of overlap between the well liner and the previously installed liner, using a tubular pull string assembly that comprises a tubular string provided with at least one flow port in the vicinity of the expansion mandrel through which fluid is permitted to flow from the exterior to the interior of the tubular string, which flow port is open when the expansion mandrel reaches, and pops out of, a top of the area of overlap.

2. The method of claim 1 , wherein the at least one flow port is arranged at a distance of less than 5 meters from the expansion mandrel.

3. The method of claim 1 , wherein the at least one flow port comprises a valve that is opened shortly before the expansion cone pops out of the area of overlap.

4. The method of claim 1 , further comprising:

providing the expansion mandrel with a streamlined tail section having an inwardly tapered outer surface that intersects a longitudinal axis of the expansion mandrel at a sharp angle which is less than 20 degrees over a length of at least 5 centimeters (cm).

5. The method of claim 4 , wherein the sharp angle is less than 15 degrees.

6. The method of claim 1 , wherein the expansion mandrel comprises a gauge section having a gauge diameter Dcone, followed by a tail section having a streamlined inwardly tapered outer surface that intersects a longitudinal axis of the expansion mandrel at a sharp angle which is less than 20 degrees and has a length of at least 5 centimeters (cm), wherein said tail section comprises two consecutive tapered zones of the angles of which, both within a range of between 9 and 13 degrees, consecutively increase at larger distances away from the gauge section, over respective lengths L4 and L5, wherein a ratio L4/Dcone is in a range of from 0.10 to 0.12 and a ratio L5/Dcone is in a range of from 0.40 to 0.46.

7. A method of expanding at least an upper section of a well liner configured within a lower section of a previously installed liner, the method comprising:

providing an expansion mandrel with a gauge section having a gauge diameter Dcone, and followed by a streamlined tail section having an inwardly tapered outer surface that intersects a longitudinal axis of the expansion mandrel at a sharp angle which is less than 20 degrees and over a length of at least 5 centimeters (cm);

pulling the expansion mandrel up through the well liner, in an area of overlap between the well liner and the previously installed liner whereby the expansion mandrel reaches, and pops out of, a top of the area of overlap;

wherein said tail section comprises two consecutive tapered zones of the angles of which, both within a range of between 9 and 13 degrees, consecutively increase at larger distances away from the gauge section, over respective lengths L4 and L5, wherein a ratio L4/Dcone is in a range of from 0.10 to 0.12 and a ratio L5/Dcone is in a range of from 0.40 to 0.46.

8. The method of claim 7 , wherein the tail section acts as a diffuser, which converts kinetic energy of the fluid around the tail section of the expansion mandrel into static pressure and thereby reduces the pressure drop in the fluid when the expansion mandrel accelerates during pop out from the area of overlap.

9. A system for expanding at least an upper section of a well liner configured within a lower section of a previously installed liner, the system comprising:

an expansion mandrel with a gauge section having a gauge diameter Dcone, and followed by a tail section having a streamlined inwardly tapered outer surface that intersects a longitudinal axis of the expansion mandrel at a sharp angle which is less than 20 degrees and has a length of at least 5 centimeters (cm);

a tubular pull string assembly that is connected to the expansion mandrel; and

wherein said tail section comprises two consecutive tapered zones of the angles of which, both within a range of between 9 and 13 degrees, consecutively increase at larger distances away from the gauge section, over respective lengths L4 and L5, wherein a ratio L4/Dcone is in a range of from 0.10 to 0.12 and a ratio L5/Dcone is in a range of from 0.40 to 0.46.

10. The system of claim 9 , wherein the sharp angle is less than 15 degrees.

11. The system of claim 9 , wherein said tubular pull string assembly comprising a tubular string provided with at least one flow port in the vicinity of the expansion mandrel through which fluid is permitted to flow from the exterior to the interior of the tubular string.

12. The system of claim 11 , wherein the at least one flow port is arranged at a distance of less than 5 meters from the expansion mandrel.

13. The system of claim 11 , wherein the at least one flow port comprises a valve.

14. An expansion mandrel for expanding of a well liner inserted at least partially inside a previously installed liner, said expansion mandrel comprising:

a pull direction side;

a gauge section having a gauge diameter Dcone;

a tail section on a side of the gauge section opposite from the pull direction side, said tail section having a streamlined inwardly tapered outer surface that intersects a longitudinal axis of the expansion mandrel at a sharp angle which is less than 20 degrees over a length of at least 5 centimeters (cm) wherein said tail section comprises two consecutive tapered zones of the angles of which, both within a range of between 9 and 13 degrees, consecutively increase at larger distances away from the gauge section, over respective lengths L4 and L5, wherein a ratio L4/Dcone is in a range of from 0.10 to 0.12 and a ratio L5/Dcone is in a range of from 0.40 to 0.46.