| 摘要 |
There is described downhole apparatus (100) and methods for identifying the position of an interface (170) within a subterranean formation. In some examples, the apparatus is for use at a fixed downhole location, such as a production zone (195), and is configured to determine the encroachment of an interface (e.g. water) into the production zone. In other examples, the apparatus is for use with a drill assembly (290) and is configured to determine the distance of a drill assembly from a subterranean interface during drilling. In some examples, the apparatus uses signals comprising a plurality of frequencies, which may be selected based on the particular subterranean interfaces being measured. |
