Deploying an untethered object in a passageway of a well

1. A method usable with a well, comprising:

providing a string comprising a passageway and a plurality of tools;

deploying an untethered object in the passageway such that the object travels downhole via the passageway; and

expanding a size of the object as the object travels downhole to cause one of the tools to capture the object, the expanding comprising using the untethered object to wirelessly sense a signal transmitted by the one of the tools and automatically expanding the size of the untethered object before the object reaches the one of the tools in response to sensing the signal.

2. The method of claim 1 , wherein

the providing comprises providing a plurality of tools comprising valves having seats, each of the seats being sized to catch an object having substantially the same size, and

the expanding causes the untethered object to expand to have said same size.

3. The method of claim 2 , further comprising:

using the captured untethered object to lodge in one of the seats to plug the string; and

subsequently pressurizing the string above the captured untethered object.

4. The method of claim 3 , further comprising opening the valve associated with said one of the seats in response to the pressurizing.

5. The method of claim 4 , further comprising treating a zone of the well, comprising communicating fluid through the opened valve.

6. The method of claim 1 , wherein the using comprises using a receiver of the untethered object to sense a signal emitted by a transmitter disposed downhole near said one of the tools.

7. The method of claim 1 , wherein

the deploying the untethered object comprises deploying a dart, and

the expanding comprises radially expanding an element of the dart to cause the dart to lodge in said one of the tools.

8. The method of claim 1 , wherein the deploying comprises pumping the untethered object downhole via the passageway.

9. The method of claim 1 , further comprising:

deploying another untethered object in the passageway such that said another untethered object travels downhole via the passageway; and

expanding a size of said another untethered object as said another untethered object travels downhole to selectively cause another one of the tools to capture said another untethered object.

10. An apparatus usable with a well, comprising:

a body adapted to travel downhole untethered via a passageway of a string extending into the well, the string comprising a tool and the string comprising at least one transmitter to transmit a wireless signal;

a receiver adapted to travel downhole with the body and receive the signal when in proximity to the tool; and

at least one member to radially expand as the body is traveling in response to the receiver sensing the signal to cause the tool to capture the body,

wherein the received signal indicates a proximity of the object to the tool.

11. The apparatus of claim 10 , wherein the apparatus comprises a dart and the tool comprises a valve comprising a seat in which said at least one member lodges to capture the body.

12. The apparatus of claim 11 , wherein said at least one member comprises a fin of the dart.

13. The apparatus of claim 10 , wherein

the tool is one of a plurality of tools on the string,

each tool of the plurality of tools having an opening being sized to catch an object having substantially the same size,

the body is adapted to pass through each of the openings when the member is not radially expanded, and

the body is adapted to not pass through any of the openings when the member is radially expanded.

14. The apparatus of claim 10 , wherein the body is adapted to be pumped downhole through the passageway of the string.

15. The apparatus of claim 10 , wherein the at least one transmitter comprises a plurality of transmitters, and the plurality of transmitters being adapted to transmit signals indicative of identifications for the transmitters.

16. The apparatus of claim 15 , wherein the identifications are unique with respect to each other.

17. A system comprising:

a string comprising a passageway and a plurality of tools; and

an untethered object adapted to:

be deployed in the passageway such that the object travels downhole via the passageway; and

controllably expand its size as the object travels downhole before the object reaches one of the tools in response to the object sensing a wireless signal transmitted by the one of the tools to cause one of the tools to capture the object.

18. The system of claim 17 , wherein

the plurality of tools comprise valves having seats, each of the seats being sized to catch an object having substantially the same size, and

the untethered object is adapted to pass through at least one of the seats and controllably expand to said same size to cause capture of the untethered object by one of the valves.

19. The system of claim 17 , wherein the untethered object is adapted to constrict flow in the passageway through said one of the valves to generate pressure to transition a state of said one of the valves.

20. The system of claim 17 , wherein the string comprises a casing that lines a wellbore of the well.

21. The system of claim 17 , wherein the untethered object comprises a dart comprising at least one fin adapted to radially expand in response to the dart approaching said one of the tools.

22. A system comprising:

a string comprising a passageway;

a plurality of valves disposed in the string and each of the valves comprising a seat, wherein each of the seats is sized to catch an object having substantially the same size traveling through the passageway of the string and each of the valves is adapted to control fluid communication between the passageway and a region exterior to the string; and

a dart adapted to:

be deployed in the passageway such that the dart travels downhole via the passageway; and

controllably expand its size as the dart travels downhole before the dart reaches one of the seats in response to the dart sensing a wireless signal transmitted by a transmitter disposed closer to the one of the seats than to any of the other seats to cause the dart to lodge in the one of the seats.

23. The system of claim 22 , further comprising:

another dart adapted to be deployed in the passageway such that said another dart travels downhole via the passageway and controllably expands its size as said another dart travels downhole to selectively cause said another dart to lodge in another one of the seats.

24. The system of claim 22 , wherein

the string comprises a transmitter disposed in proximity to said one of the seats, the transmitter adapted to transmit a wireless signal; and

the dart comprises at least one fin and a receiver adapted to sense the wireless signal to cause the dart to expand said at least one fin to cause the dart to lodge in said one of the seats.