Numerical simulation of azimuthal acoustic logging in a borehole penetrating a rock formation boundary

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Abstract
We have developed a new 3D acoustic logging tool (3DAC). To examine the azimuthal resolution of 3DAC, we have evaluated a 3D finite-difference time-domain model to simulate a case in which the borehole penetrated a rock formation boundary when the tool worked at the azimuthal-transmitting-azimuthal-receiving mode. The results indicated that there were two types of P-waves with different slowness in waveforms: the P-wave of the harder rock (P1) and the P-wave of the softer rock (P2). The P1-wave can be observed in each azimuthal receiver, but the P2-wave appears only in the azimuthal receivers toward the softer rock. When these two types of rock are both fast formations, two types of S-waves also exist, and they have better azimuthal sensitivity compared with P-waves. The S-wave of the harder rock (S1) appears only in receivers toward the harder rock, and the S-wave of the softer rock (S2) appears only in receivers toward the softer rock. A model was simulated in which the boundary between shale and sand penetrated the borehole but not the borehole axis. The P-wave of shale and the S-wave of sand are azimuthally sensitive to the azimuth angle variation of two formations. In addition, waveforms obtained from 3DAC working at the monopole-transmitting-azimuthal-receiving mode indicate that the corresponding P-waves and S-waves are azimuthally sensitive, too. Finally, we have developed a field example of 3DAC to support our simulation results: The azimuthal variation of the P-wave slowness was observed and can thus be used to reflect the azimuthal heterogeneity of formations.
Funding Information
  • National Natural Science Foundation of China (11204380)
  • National Natural Science Foundation of China (11374371)
  • National Natural Science Foundation of China (61102102)
  • National Natural Science Foundation of China (11134011)
  • National Science and Technology Major Project (2011ZX05020-009)
  • China National Petroleum Corporation (2014B-4011)
  • China National Petroleum Corporation (2014D-4105)
  • China National Petroleum Corporation (2014A-3912)
  • PetroChina Innovation Foundation (2013D-5006-0304)
  • PetroChina Innovation Foundation (2014D-5006-0307)

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