Method and apparatus for logging underground formations using radar

摘要

A method of logging an underground formation from within a borehole includes the steps of emitting an electromagnetic signal from a first location in a borehole, determining a time at which the signal is emitted, detecting a direct component of the signal which has passed from the first location to a second location without being reflected, determining a time at which the direct component arrives at the second location and determining the speed of the signal in the underground formation from the time at which the signal is emitted, the time of arrival of the direct component and the spacing of the first and second locations. The speed of the signal can be used for radar logging of the formation. A logging tool for performing the method includes a transmitter at a first position in a tool body for emitting an electromagnetic signal, means located in the tool body for determining a time at which the signal is emitted, a receiver at a second position in the tool body for detecting a signal which has passed from the transmitter to the receiver through an underground formation; and means located in the tool body for processing the detected signal using the time at which a corresponding signal is emitted from the transmitter.