Imaging of formation structure ahead of the drill-bit

摘要

The present disclosure is related to apparatuses and methods for downhole acoustic logging. The tool may be used for generating a guided borehole wave that propagates into the formation as a body wave, reflects from an interface, and is converted back into a guided borehole wave. Guided borehole waves resulting from reflection of the body wave are used to image a reflector. Methods may include processing of acoustic logging signals including: wavefield separation, auto-correlation of wavefield components, filtering using a dip filter, and estimating a distance to the reflective interface.

主权项

1. A method of determining a distance to an interface in an earth formation, the method comprising:
(a) conveying a logging instrument into a borehole; (b) activating at least one transmitter on the logging instrument to produce a guided acoustic wave which propagates downward to the bottom of the borehole and produces an acoustic wave in the earth formation; (c) using at least one receiver on the logging instrument to:
receive a first signal responsive to the downward propagating guided acoustic wave, andreceive a second signal responsive to an upward propagating guided acoustic wave resulting from reflection of the acoustic wave in the formation at an interface therein; (d) auto-correlating the first signal and the second signal; (e) filtering the auto-correlated first signal and the auto-correlated second signal using a dip filter; and (f) estimating from the filtered auto-correlated first signal and the filtered auto-correlated second signal a distance to the interface.