Method and apparatus for fracture detection along surfaces and boreholes by means of ultrasonic echography

摘要

A method and apparatus of detecting fractures along the wall of a formation, such as a well formed by test-drilling, provides for the transmission of ultrasonic signals in a direction essentially perpendicular to the wall from a position spaced from the wall by a predetermined distance and the reception of the ultrasonic signals which may be reflected by the wall. The space of predetermined thickness between the transducer which generates the ultrasonic signals and the wall is filled with an intermediate material which does not form a distinct interface with the wall of the type which would be able to produce an appreciable parasitic reflection of the transmitted signals. With this arrangement, if the transducer receives a reflected ultrasonic signal during a time window which begins, following the time of transmission, after a time has elapsed which is essentially equal to the out-and-back travel time of the ultrasonic signals through the space of predetermined thickness, then it will be determined that the wall has no fractures at that point. If no signal is received during the time window, the presence of fractures or small cavities is detected.