Apparatus and methods for providing information about one or more subterranean variables

摘要

In some embodiments, a method of obtaining information about at least one variable existing at a target location in an underground well bore and/or surrounding subterranean formation includes delivering a plurality of signal generating devices to the target location(s), emitting at least one detectable signal from the target location and receiving at least one such signal. Information about the variable(s) is derived from at least some of the received signals.