A monitoring apparatus for use in a well can include multiple segments, the segments comprising at least one buoyancy control device, at least one communication device, and at least one well parameter sensor. A method of communicating in a subterranean well can include installing at least one monitoring apparatus in the well, the monitoring apparatus including a communication device, a well parameter sensor and a buoyancy control device, and the communication device communicating with another communication device. A well monitoring system can include at least one monitoring apparatus disposed in a wellbore, the monitoring apparatus comprising multiple segments, the segments including at least one buoyancy control device, at least one well parameter sensor, and at least one communication device.