Liquid spring communication sub

1. A communications sub, comprising:

a fluid chamber;

a pressure-activated indexing device positioned within the fluid chamber, the pressure-activated indexing device including a lock mandrel configured to incrementally move between an engaged state and a disengaged state when subjected to two or more pressure cycles; and

a latch body positioned in the fluid chamber, the latch body configured to be fixed in place by the lock mandrel and close a fluid path from the fluid chamber to a control line when the lock mandrel is in the engaged state, and configured to be allowed to move and open the fluid path from the fluid chamber to the control line when the lock mandrel is in the disengaged state, wherein the lock mandrel radially supports the latch body when in the engaged state and radially de-supports the latch body when in the disengaged state.

2. The communications sub as recited in claim 1 , wherein the latch body includes a collet configured to engage with a profile in an outer housing to keep the latch body fixed in place when the lock mandrel is in the engaged state and configured to disengage from the profile to allow the lock mandrel to move when the lock mandrel is in the disengaged state.

3. The communications sub as recited in claim 1 , wherein the latch body includes a seal member, the seal member configured to engage with one or more seals to close the fluid path from the fluid chamber to the control line when the latch body is fixed in place and open the fluid path from the fluid chamber to the control line when allowed to move.

4. The communications sub as recited in claim 1 , further including a spring member coupled to the latch body, the spring member configured to move the latch body when the lock mandrel moves from the engaged state to the disengaged state.

5. The communications sub as recited in claim 1 , further including an inner tubing string, an outer housing, and a floating piston located in an annulus between the inner tubing string and the outer housing, the floating piston defining the fluid chamber.

6. The communications sub as recited in claim 5 , wherein the fluid chamber includes a fluid restrictor positioned therein, the fluid restrictor separating the fluid chamber into a low-pressure fluid chamber and a high-pressure fluid chamber.

7. A method for activating a downhole device, comprising:

providing a communications sub, the communications sub including:

a fluid chamber;

a pressure-activated indexing device positioned within the fluid chamber, the pressure-activated indexing device including a lock mandrel configured to incrementally move between an engaged state and a disengaged state; and

a latch body positioned in the fluid chamber, the latch body configured to be fixed in place by the lock mandrel and close a fluid path from the fluid chamber to a control line when the lock mandrel is in the engaged state, and configured to be allowed to move and open the fluid path from the fluid chamber to the control line when the lock mandrel is in the disengaged state, wherein the lock mandrel radially supports the latch body when in the engaged state and radially de-supports the latch body when in the disengaged state; and

subjecting the pressure-activated indexing device to two or more pressure cycles to move the lock mandrel between the engaged state and the disengaged state and allow the latch body to move to open the fluid path between the fluid chamber and the control line coupled to a downhole device.

8. The method as recited in claim 7 , wherein subjecting the pressure-activated indexing device to two or more pressure cycles opens the fluid path between the fluid chamber and the control line to activate the downhole device.

9. The method as recited in claim 7 , wherein the latch body includes a collet configured to engage with a profile in an outer housing to keep the latch body fixed in place when the lock mandrel is in the engaged state and configured to disengage from the profile to allow the lock mandrel to move when the lock mandrel is in the disengaged state.

10. The method as recited in claim 7 , wherein the latch body includes a seal member, the seal member configured to engage with one or more seals to close the fluid path from the fluid chamber to the control line when the latch body is fixed in place and open the fluid path from the fluid chamber to the control line when allowed to move.

11. The method as recited in claim 7 , further including a spring member coupled to the latch body, the spring member configured to move the latch body when the lock mandrel moves from the engaged state to the disengaged state.

12. The method as recited in claim 7 , further including an inner tubing string, an outer housing, and a floating piston located in an annulus between the inner tubing string and the outer housing, the floating piston defining the fluid chamber.

13. The method as recited in claim 12 , wherein the fluid chamber includes a fluid restrictor positioned therein, the fluid restrictor separating the fluid chamber into a low-pressure fluid chamber and a high-pressure fluid chamber.

14. A well system, comprising:

a wellbore located in a subterranean formation;

a tubing string located within the wellbore;

a communications sub coupled with the tubing string, the communications sub including:

a fluid chamber;

a pressure-activated indexing device positioned within the fluid chamber, the pressure-activated indexing device including a lock mandrel configured to incrementally move between an engaged state and a disengaged state when subjected to two or more pressure cycles; and

a latch body positioned in the fluid chamber, the latch body configured to be fixed in place by the lock mandrel and close a fluid path from the fluid chamber to a control line when the lock mandrel is in the engaged state, and configured to be allowed to move and open the fluid path from the fluid chamber to the control line when the lock mandrel is in the disengaged state, wherein the lock mandrel radially supports the latch body when in the engaged state and radially de-supports the latch body when in the disengaged state; and

a downhole device coupled to the control line.

15. The well system as recited in claim 14 , wherein the latch body includes a collet configured to engage with a profile in an outer housing to keep the latch body fixed in place when the lock mandrel is in the engaged state and configured to disengage from the profile to allow the lock mandrel to move when the lock mandrel is in the disengaged state.

16. The well system as recited in claim 14 , wherein the latch body includes a seal member, the seal member configured to engage with one or more seals to close the fluid path from the fluid chamber to the control line when the latch body is fixed in place and open the fluid path from the fluid chamber to the control line when allowed to move.

17. The well system as recited in claim 14 , further including a spring member coupled to the latch body, the spring member configured to move the latch body when the lock mandrel moves from the engaged state to the disengaged state.

18. The well system as recited in claim 14 , further including an inner tubing string, an outer housing, and a floating piston located in an annulus between the inner tubing string and the outer housing, the floating piston defining the fluid chamber.

19. The well system as recited in claim 18 , wherein the fluid chamber includes a fluid restrictor positioned therein, the fluid restrictor separating the fluid chamber into a low-pressure fluid chamber and a high-pressure fluid chamber.