Stage cementing system

1. A stage cementing system, comprising:

a stage cementing assembly having a stage tool, the stage tool comprising:

an outer mandrel,

an inner mandrel coupled to and disposed inside of the outer mandrel,

an annular chamber between the outer mandrel and the inner mandrel,

a first outer port through the outer mandrel, and

longitudinally spaced first and second inner ports through the inner mandrel; and

an inner string assembly configured to be located inside the inner mandrel, the inner string assembly comprising:

a tubular body having a central throughbore and longitudinally spaced first and second side ports,

a lower external seal element below the first and second side ports,

a middle external seal element between the first and second side ports,

an upper external seal element above the first and second side ports, and

a bypass configured to fluidically connect a first zone below the lower external seal element with a second zone above the upper external seal element.

2. The stage cementing system of claim 1 , wherein the stage tool further comprises a closing sleeve disposed in the annular chamber, the closing sleeve movable between:

a first position in which the closing sleeve permits fluid communication between an interior of the stage cementing assembly and an exterior of the stage cementing assembly through the first inner port and the first outer port, and

a second position in which the closing sleeve prevents fluid communication between the interior of the stage cementing assembly and the exterior of the stage cementing assembly through the first inner port and the first outer port.

3. The stage cementing system of claim 2 , wherein the closing sleeve is actuated to the second position by an application of hydraulic pressure through the second inner port.

4. The stage cementing system of claim 1 , wherein in use:

the middle external seal element is located between the first and second inner ports of the stage tool;

the lower external seal element is located below the first and second inner ports of the stage tool; and

the upper external seal element is located above the first and second inner ports of the stage tool.

5. The stage cementing system of claim 4 , wherein the lower, middle, and upper external seal elements contact an inner wall of the inner mandrel.

6. The stage cementing system of claim 1 , wherein an interior of the inner mandrel does not include an internal movable sleeve.

7. The stage cementing system of claim 1 , wherein the stage tool further comprises a second outer port through the outer mandrel, the second outer port having a relief valve.

8. The stage cementing system of claim 1 , wherein the stage cementing assembly further comprises a packer coupled to the stage tool.

9. The stage cementing system of claim 1 , wherein the stage cementing assembly has an internal location profile configured for engagement with a locator of the inner string assembly.

10. The stage cementing system of claim 1 , wherein the inner string assembly includes a relief port configured to fluidically connect a third zone between the upper and middle external seal elements with the bypass.

11. A method of cementing a casing string including a stage tool, the method comprising:

pumping a first fluid through an inner string located inside the casing string, into a first annular space below the stage tool, and through a bypass of the inner string into a second annular space above the stage tool;

then opening a first side port of the inner string;

pumping a cementing second fluid through the first side port, into a third annular space between the inner string and the casing string, through a first inner port of an inner mandrel of the stage tool, and a first outer port of an outer mandrel of the stage tool;

then opening a second side port of the inner string; and

applying a hydraulic pressure through the second side port into a fourth annular space between the inner string and the casing string, and through a second inner port of the inner mandrel of the stage tool, thereby moving a closing sleeve of the stage tool to a position preventing fluid flow through the first outer port.

12. The method of claim 11 , further comprising engaging a locator of the inner string with an internal location profile of the casing string.

13. The method of claim 11 , further comprising setting a packer coupled to the stage tool after opening the first side port and before causing the cementing second fluid to flow through the first outer port of the outer mandrel of the stage tool.

14. The method of claim 11 , further comprising defeating a barrier member before causing the cementing second fluid to flow through the first outer port of the outer mandrel of the stage tool.

15. The method of claim 11 , further comprising applying a test pressure to the stage tool after moving the closing sleeve of the stage tool to the position preventing fluid flow through the first outer port.

16. The method of claim 11 , wherein:

opening the first side port further comprises landing a first actuating object in a first seat associated with the first side port, and applying a first opening pressure to the first actuating object;

opening the second side port further comprises landing a second actuating object in a second seat associated with the second side port, and applying a second opening pressure to the second actuating object; and

displacing the first and second actuating objects to a time-delay releasable seat after moving the closing sleeve of the stage tool to the position preventing fluid flow through the first outer port, and before pressure testing the stage tool by applying a test pressure via the inner string.

17. The method of claim 16 , further comprising:

applying the test pressure to the second actuating object, thereby moving a sleeve of the time-delay releasable seat from a seat-retaining position to a seat-releasing position; and

then causing the first and second actuating objects to move to a catcher.

18. The method of claim 11 , further comprising retrieving the inner string from the casing string.

19. The method of claim 11 , further comprising:

opening a circulation port of the inner string prior to pumping the first fluid into the first annular space.