A Study For Fluid-filled Borehole Acoustic Wave Propagation Rules In Transverse Isotropic Media

In order to study the acoustic propagation rules in fluid-filled borehole of transversely anisotropic formation, this thesis carries out borehole acoustic field numerical simulation excited by multipole acoustic source with discrete wave number method, on the basis of Biot acoustic wave propagation mechanism in porous media.Through the numerical simulation of the borehole acoustic field excited by the multipole acoustic source in the homogeneous isotropic porous medium, the acoustic velocity and the attenuation of the stoneley wave are both affected by formation permeability, the theoretical basis for integrating the acoustic velocity and attenuation of the stoneley wave to invert permeability. Different with stoneley wave, the velocity of the flexural wave is almost not affected by formation permeability while its attenuation increases with the increasing permeability. This provides possibility for the attenuation of the flexural wave to invert formation permeability.A formation model with transverse anisotropy is built. The effects of formation parameters, such as formation permeability and gas saturation, on the characteristic attributes of stoneley wave excited by monopole acoustic source and flexural wave excited by dipole are studied in terms of dispersive curve, attenuation curve and full waveform, respectively. On this basis, a racially layered formation model is built to analyse the sensitivity of mode wave to formation parameters, and further the investigation depth of the mode wave is given. As to transversely anisotropic formation, regardless of soft or hard formation, the longitudinal permeability shows little effect on the mode wave, nearly equal to zero, while the presence of gas in formation affects the amplitude of the mode wave greatly. Thereby it is considerable to utilize the attenuation of the borehole mode wave and the change of main frequency to recognize gas formation. Through the sensitive analysis of mode waves to original formation parameters, it is demonstrated that the investigation depth of the flexural wave is larger than that of the stoneley wave.