Top plug with transitionable seal

1. A plug, comprising:

a housing having:

a head end;

a tail end; and

a bore extending from the head end to the tail end; and

at least one shearable member; and

a transitionable seal, wherein:

the transitionable seal is partially disposed outside of the housing and seals the bore of the housing when in a first configuration, wherein the transitional seal is in the first configuration prior to the deployment of the plug into a wellbore,

the transitionable seal is attached to the housing by the at least one shearable member in the first configuration,

the transitionable seal unseals the bore when in a second configuration, and

the transitionable seal is triggerable to transition from the first configuration to the second configuration.

2. The plug of claim 1 , wherein the transitionable seal seals the bore of the housing when in an intermediate configuration that is between the first configuration and the second configuration.

3. The plug of claim 1 , wherein the transitionable seal is an expendable cap, wherein the at least one shearable member holds the expendable cap in the housing when in the first configuration, the plug further comprising:

a spring element biased when in the first configuration, and configured to eject the expendable cap from the housing when in the second configuration.

4. The plug of claim 1 , wherein the transitionable seal is an expendable cap that blocks no more than half of a cross-sectional area of the bore at the tail end of the housing when in the second configuration.

5. The plug of claim 1 , wherein the transitionable seal is a sleeve, comprising:

a plurality of sleeve passages that align with ports in the housing when in the second configuration; and

a j-slot that engages with a pin of the housing.

6. The plug of claim 1 , further comprising a recess between the transitionable seal and the housing when in the first configuration, wherein the transitionable seal enters the recess during transition between the first configuration and the second configuration.

7. The plug of claim 1 , wherein the transitionable seal is triggerable by a pressure signal.

8. The plug of claim 7 , wherein either a pressure-drop signal or a multi-step pressure signal causes the transitionable seal to unseal the bore.

9. The plug of claim 1 , further including a reservoir of a dissolving fluid, wherein the bore is unsealed in the second configuration after the transitionable seal is dissolved by the dissolving fluid.

10. A plug, comprising:

a housing having a flow path; and

a transitionable seal releasably fastened to the housing and partially disposed outside the housing in a first position, wherein:

the transitionable seal is configured to unfasten from the housing in response to a pressure increase of a fluid and move to a second position,

the transitionable seal is configured to move from the second position to a third position in response to a pressure decrease of the fluid, and

wherein:

the flow path is sealed when the transitionable seal is in the first and the second position, and

the flow path is unsealed when the transitionable seal is in the third position.

11. The plug of claim 10 , wherein the transitionable seal is an expendable cap including one or more seal members.

12. The plug of claim 10 , further comprising a biasing member between the transitionable seal and the housing configured to move the transitionable seal to the third position in response to the pressure decrease.

13. The plug of claim 12 , wherein the transitionable seal is ejected from the housing in the third position.

14. The plug of claim 10 , wherein the transitionable seal is a sleeve, comprising:

a plurality of sleeve passages that align with a plurality of ports in the housing when in the second position; and

a j-slot that engages with a pin of the housing.

15. The plug of claim 10 , wherein the transitionable seal is fastened to the housing in the first position by one or more shear pins, wherein the transitionable seal includes:

a stopper portion; and

one or more O-rings around the stopper portion.

16. The plug of claim 10 , wherein the transitionable seal is releasably fastened to the housing in the first position by one or more shear pins.

17. The plug of claim 10 , further including at least one of a charge or magnet to assist a biasing member in moving the transitionable seal to the third position.

18. A method of using a plug, comprising:

increasing pressure of a fluid in a wellbore to move a transitionable seal of a plug that is partially disposed outside a housing of the plug from a first position to a second position, wherein a flow path of the plug remains blocked by the transitionable seal in the second position;

decreasing pressure of the fluid to move the transitionable seal from the second position to a third position, wherein the flow path is unblocked when the transitionable seal is in the third position.

19. The method of claim 18 , wherein the plug includes a biasing member configured to move the transitionable seal to the third position in response to the pressure decrease.

20. The method of claim 18 , further comprising:

performing a pressure test, wherein the pressure test includes the increasing of the pressure of the fluid to move the transitionable seal of the plug from the first position to the second position.

21. A plug, comprising:

a housing having:

a head end;

a tail end; and

a bore extending from the head end to the tail end; and

at least one shearable member; and

a transitionable seal, wherein the transitionable seal is an expendable cap, wherein:

the transitionable seal seals the bore of the housing when in a first configuration,

the transitionable seal is attached to the housing by the at least one shearable member in the first configuration, wherein the at least one shearable member holds the transitionable seal in the housing when in the first configuration,

the transitionable seal unseals the bore when in a second configuration, and

the transitionable seal is triggerable to transition from the first configuration to the second configuration; and

a spring element biased when in the first configuration, and configured to eject the transitionable seal from the housing when in the second configuration.