System and method for investigating sub-surface features of a rock formation with acoustic sources generating conical broadcast signals

摘要

A method of interrogating a formation includes generating a conical acoustic signal, at a first frequency—a second conical acoustic signal at a second frequency each in the between approximately 500 Hz and 500 kHz such that the signals intersect in a desired intersection volume outside the borehole. The method further includes receiving, a difference signal returning to the borehole resulting from a non-linear mixing of the signals in a mixing zone within the intersection volume.

主权项

1. A method of investigating rock formations outside a borehole, the method comprising:
generating, by a first acoustic source disposed within a borehole, a first conical acoustic signal, the first conical acoustic signal being broadcast at a first frequency; generating, by a second acoustic source disposed within the borehole, a second conical acoustic signal, the second conical acoustic signal being broadcast at a second frequency different from the first frequency, the first frequency and the second frequency being in the frequency range between approximately 500 Hz and 500 kHz, configuring the first acoustic source and the second acoustic source so that the first conical acoustic signal and the second conical acoustic signal intersect in a desired intersection volume within the rock formations outside the borehole; and receiving, by a receiver disposed within the borehole, a detected signal returning to the borehole having a frequency equal to a difference between the first frequency and the second frequency, the detected signal being generated by a non-linear mixing process from the first conical acoustic signal and the second conical acoustic signal in a non-linear mixing zone within the intersection volume; recording the detected signal and storing the detected signal in a storage device; and recording, in the storage device, measurement parameters including a position of the first acoustic source, a position of the second acoustic source, a position of the receiver, and a cone angle and a cone axis orientation of the first signal and a cone angle and a cone axis orientation of second conical acoustic signal to determine a position of the intersection volume where the detected signal is generated and map the detected signal to the position of the intersection volume to characterize the rock formations.