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Stoneley wave generation by an incident P‐wave propagating in the surrounding formation across a horizontal fluid‐filled fracture
Author(s) -
Ionov Andrei M.
Publication year - 2007
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.2006.00577.x
Subject(s) - borehole , amplitude , mechanics , wavelength , wave propagation , geology , fracture (geology) , acoustics , physics , optics , geotechnical engineering
This study investigates the generation of the low‐frequency borehole Stoneley wave (tube wave) by a plane P‐wave propagating through the surrounding elastic formation, which is intersected by a fluid‐filled fracture. A model is constructed taking into account the dynamic fluid coupling between the borehole interior and the fluid‐filled fracture of infinite extent with parallel walls. The basic mechanism of such coupling is due to the contraction of the fracture walls by the incident P‐wave, leading to seismic radiation into the fracture. The dynamic fluid flux from the fracture into the borehole interior, and vice versa, is the source of the low‐frequency Stoneley wave. An expression for the monopole pressure source, exciting the tube wave, is obtained. The tube‐wave equation in the long‐wave approximation is derived in the presence of a fluid‐filled fracture of infinite extent. Amplitudes and waveforms of Stoneley waves are analysed in the seismic wavelength range for P‐wave pulses of various shapes. It is shown that the amplitude and waveform of the Stoneley wave depends significantly on the two dimensionless parameters of the problem: (1) the ratio of the borehole radius to the dominant wavelength of the incident pulse; (2) the ratio of the fracture width to the borehole radius. It is found that the amplitude of the generated Stoneley wave can be of the order of the P‐wave amplitude in the borehole fluid. Stoneley waveforms are found to be completely different from those of the incident pulse.