Selectively degradable passage restriction

1. An actuation system comprising:

a tubular having a passage; and

an assembly disposed with the tubular, the assembly including a degradable restriction, the restriction only partially blocking the passage prior to being degraded, the degradable restriction forming a seat configured to receive a restrictor thereon to block fluid flow through the passage, the assembly configured to be actuated by creating a pressure differential across the restrictor to shift the degradable restriction and the restrictor seated thereon longitudinally with respect to the tubular prior to the restriction being degraded, and the assembly further configured to release the restrictor when the restriction is degraded.

2. The system of claim 1 , further comprising a protective layer on a degradable material of the restriction, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid, wherein the degradable material includes an uncovered area with respect to the protective layer.

3. The system of claim 2 , wherein at least one seal element is included to isolate the uncovered area from the fluid.

4. The system of claim 2 , wherein actuation of the assembly establishes fluid communication between the uncovered area and the passage.

5. The system of claim 4 , wherein fluid communication between the uncovered area and the passage is enabled by a cavity in the tubular, the cavity misaligned with the uncovered area before actuation.

6. The system of claim 2 , wherein the seat is formed at an uphole end of the restriction and the uncovered area is limited to a downhole end of the restriction.

7. The system of claim 1 , wherein actuation of the assembly opens at least one port in the tubular.

8. The system of claim 7 , wherein the assembly includes a sleeve disposed radially between the restriction and the tubular and actuation of the assembly shifts the sleeve to open the at least one port.

9. The system of claim 1 , wherein a degradable material of the restriction is entirely encapsulated by a protective layer, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid.

10. The system of claim 1 , further comprising a protective layer on a degradable material of the restriction, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid, wherein actuation of the assembly causes at least one penetration element to penetrate the protective layer for exposing the degradable material to the fluid.

11. The system of claim 1 , wherein a degradable material of the degradable restriction is a controlled electrolytic metallic material.

12. An actuation system comprising:

a tubular having a passage; and

an assembly disposed with the tubular, the assembly including a degradable restriction, the restriction only partially blocking the passage prior to being degraded, a protective layer on a degradable material of the restriction, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid, wherein the degradable material includes an uncovered area with respect to the protective layer, the assembly configured to receive and prevent further movement of a restrictor through the tubular prior to the restriction being degraded, the assembly further configured to release the restrictor when the restriction is degraded;

wherein the uncovered area is located on an extension from the restriction, the extension operatively arranged to delay degradation of the restriction until the extension is first degraded.

13. A method of operating the downhole system of claim 1 , comprising:

launching the restrictor through the passage in the tubular;

receiving the restrictor at the restriction of the assembly; and,

actuating the assembly with the restrictor for performing a primary function of the assembly.

14. The method of claim 13 , wherein the primary function of the assembly is to selectively open at least one port in the tubular.

15. The method of claim 13 , wherein actuating the assembly aligns an uncovered area of the degradable material with a cavity in the tubular, the cavity establishing fluid communication between the uncovered area and the passage.

16. The method of claim 13 , wherein the degradable material is entirely encapsulated by the protective layer and actuation of the assembly causes at least one penetrating element to penetrate the protective layer for exposing the degradable material to the fluid.

17. An actuation system, comprising:

a tubular defining a passage; and

an assembly disposed within the tubular, the assembly having a restriction operatively arranged for receiving a restrictor, the restrictor enabling actuation of the assembly, the restriction at least partially formed from a degradable material responsive to a fluid in the passage, a protective layer disposed on the degradable material, the degradable material including an uncovered area with respect to the protective layer, the uncovered area located on an extension from the restriction, wherein actuating the assembly performs a primary function, the extension operatively arranged to delay degradation of the restriction until the extension is first degraded.

18. The actuation system of claim 17 , wherein the extension extends longitudinally from the restriction, and the extension is coated by the protective layer except for the uncovered area.

19. The system of claim 17 , wherein the extension extends from a main body of the restriction, the extension having a smaller radial thickness than the main body.

20. The system of claim 17 , wherein the restriction includes a seat configured to receive the restrictor at an uphole end of the restriction, and the uncovered area is limited to a downhole end of the restriction.