<p>Acoustic logging while drilling (LWD) is one of the most advanced in-situ sonic measurements in geophysical prospecting and petroleum engineering. To investigate the acoustic fields of LWD, we develop the 3D finite-difference in cylindrical coordinates for numerical simulations of wave propagation in radially layered structures. The proposed algorithm aims to solve the excessive size inflation of grid cells in the far fields. We compensate inflation of grid cells by refining the spatial step in the azimuthal direction. The key feature of the algorithm is the establishment of bidirectional FFT interpolation at the discontinuous grid areas, which combines interpolation inwards and outwards. And the data transmission based on MPI in overlapping zone eliminates the artificial reflection after sharp changes of the grid azimuth step size. In numerical examples, we analyze the acoustic signals of LWD in a fluid-filled borehole intersecting with fractures. It is revealed that mode conversion occurs between the collar and the Stoneley waves at the discontinuity of the borehole wall. And parts of scattered Stoneley waves can even leak through those fluid-filled fractures. Due to the shielding effect of the rigid drill pipe, the received signals in varying azimuths evaluated the directions of reflectors according to the echo amplitudes. As the tool rotates during downhole measurements, it can scan the azimuthal reflectors continuously. By evaluating reflection moveouts and amplitudes at the sensor arrays, one can recognize the azimuths and inclinations of geological interfaces outside the borehole.</p>

Acoustic Fields of Logging While Drilling in Heterogeneous Formations: Numerical Simulations

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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