Downhole fluid detection using surface waves

1. A communication system that is positionable in a wellbore, the communication system comprising:

a first transceiver positioned externally to a casing string and operable to detect a presence or an absence of a surface wave, determine a location of a fluid in the wellbore based on the presence or the absence of the surface wave, and transmit data indicative of the location to a second transceiver, wherein the surface wave comprises an electromagnetic wave that includes a magnetic field or an electric field that is non-transverse to a direction of propagation of the surface wave; and

the second transceiver positioned externally to the casing string and operable to receive the data.

2. The communication system of claim 1 , wherein the first transceiver is electrically coupled to a sensor comprising a pressure sensor, a temperature sensor, a microphone, a resistivity sensor, a vibration sensor, or a fluid flow sensor for determining a characteristic of the fluid, the casing string, or a cement sheath.

3. The communication system of claim 2 , wherein the first transceiver comprises:

a processing device; and

a memory device in which instructions executable by the processing device are stored for causing the processing device to:

receive a sensor signal from the sensor;

determine a property of the wellbore or the fluid based on the sensor signal;

select a transmission mode from a plurality of transmission modes based on the property; and

transmit a signal using the transmission mode and indicating the location.

4. The communication system of claim 3 , wherein the plurality of transmission modes comprise magnetic induction, acoustic transmissions, vibrations, mud pulse telemetry, surface waves, radio frequency communications, and pulsed optical signals.

5. The communication system of claim 1 , wherein the first transceiver comprises:

a processing device; and

a memory device in which instructions executable by the processing device are stored for causing the processing device to:

receive a wireless communication from another transceiver;

determine a characteristic of the wireless communication;

determine a property of the wellbore or the fluid based on the characteristic;

select a transmission mode from a plurality of transmission modes based on the property; and

transmit a signal using the transmission mode and indicating the location.

6. The communication system of claim 1 , wherein the second transceiver is positioned on a second casing string with an inner diameter that is larger than an outer diameter of the casing string.

7. The communication system of claim 1 , further comprising a third transceiver positioned within a well tool, wherein the second transceiver is operable to relay the data to the third transceiver, and the third transceiver is operable to relay the data to a surface of the wellbore via a wireline or fiber optic cable.

8. The communication system of claim 1 , wherein the first transceiver and the second transceiver are positioned for generating and detecting surface waves that propagate along an interface surface between the casing string and a cement sheath.

9. A system comprising:

a first transceiver positioned externally to a casing string for detecting surface waves in a wellbore and communicating data, wherein the surface waves each comprise a magnetic field or an electric field that is non-transverse to a direction of propagation of the surface waves; and

a second transceiver coupled to the casing string for receiving the data for determining a location of a fluid in the wellbore based on the data.

10. The system of claim 9 , wherein the first transceiver is electrically coupled to a sensor comprising a pressure sensor, a temperature sensor, a microphone, a resistivity sensor, a vibration sensor, or a fluid flow sensor for determining a characteristic of the fluid, the casing string, or a cement sheath.

11. The system of claim 10 , wherein the first transceiver comprises:

a processing device; and

a memory device in which instructions executable by the processing device are stored for causing the processing device to:

receive a sensor signal from the sensor;

determine a property of the wellbore or the fluid based on the sensor signal;

select a transmission mode from a plurality of transmission modes based on the property; and

transmit a signal using the transmission mode and indicating a presence or an absence of the surface waves.

12. The system of claim 11 , wherein the plurality of transmission modes comprise magnetic induction, acoustic transmissions, vibrations, mud pulse telemetry, surface waves, radio frequency communications, and pulsed optical signals.

13. The system of claim 9 , wherein the first transceiver comprises:

a processing device; and

a memory device in which instructions executable by the processing device are stored for causing the processing device to:

receive a wireless communication from another transceiver;

determine a characteristic of the wireless communication;

determine a property of the wellbore or the fluid based on the characteristic;

select a transmission mode from a plurality of transmission modes based on the property; and

transmit a signal using the transmission mode and indicating a presence or an absence of the surface waves.

14. The system of claim 9 , wherein the first transceiver is positioned on a second casing string with an inner diameter that is larger than an outer diameter of the casing string.

15. The system of claim 9 , further comprising a third transceiver positioned within a well tool, wherein the second transceiver is operable to relay the data to the third transceiver, and the third transceiver is operable to relay the data to a surface of the wellbore via a wireline or fiber optic cable.

16. The system of claim 9 , wherein the first transceiver and the second transceiver are positioned for generating and detecting the surface waves that propagate along an interface surface between the casing string and a cement sheath.

17. The system of claim 9 , wherein the first transceiver comprises an antenna positioned coaxially around the casing string for detecting the surface waves.

18. A method comprising:

detecting, by a transceiver positioned externally to a casing string, a presence or an absence of a surface wave that comprises an electromagnetic wave with a magnetic field or an electric field that is non-transverse to a direction of propagation of the surface wave;

determining, by the transceiver, a location of a fluid in a wellbore based on the presence or the absence of the surface wave; and

transmitting, by the transceiver, data indicative of the location to a second transceiver.

19. The method of claim 18 , further comprising:

receiving a sensor signal from a sensor;

determining a property of the wellbore or the fluid based on the sensor signal;

selecting a transmission mode from a plurality of transmission modes based on the property, wherein the plurality of transmission modes comprise magnetic induction, acoustic transmissions, vibrations, mud pulse telemetry, surface waves, radio frequency communications, and pulsed optical signals; and

transmitting a signal using the transmission mode and indicating the presence or the absence of the surface wave.

20. The method of claim 18 , further comprising:

receiving a wireless communication from another transceiver;

determining a characteristic of the wireless communication;

determining a property of the wellbore or the fluid based on the characteristic;

selecting a transmission mode from a plurality of transmission modes based on the property; and

transmitting a signal using the transmission mode and indicating the presence or the absence of the surface wave.