Numerical study on 3D acoustic field in borehole generated by eccentric sources

Abstract

Two new tools for well logging, circumferential acoustic device (CAD) and sector bond test (SBT), are used in oil fields in which the transmitting transducers are either pressed onto or located close to the borehole wall and the acoustic field thus generated is three-dimensional. We calculated the acoustic field along a fluid-filled cylindrical borehole in an elastic medium generated by a point source in the hole and close to the wall. The method called real axis integral is used. The spectrum of the acoustic field in the domain of the frequency and axial wave number is expressed as an infinite series of Bessel functions. Its truncation is analyzed which is dependent on the frequency and radius of the borehole. In the calculation Bessel functions up to the 60th order are used. The spectrum is first calculated and then transformed to the time-space domain. The waveforms at some receiving positions and some snapshots are given in the paper. It is shown that the field consists of the direct wave, reflected waves, and interface longitudinal and transverse waves. [Work supported by Nature Science Foundation of China, No. 19974059.]