Dipole Flexural Waves Splitting Induced by Borehole Pressurization and Formation Stress Concentration

Abstract

We numerically calculate the Stoneley and flexural mode dispersion curves in a fluid‐filled borehole with borehole pressurization and uniaxially stressed solid formation. From the computational results of sensitivity coefficients and velocity‐stress coefficients, we show that the sensitivity coefficient without the third‐order elastic constant is larger than the other sensitivity coefficients , but the velocity‐stress coefficient corresponding to it is less than the other velocity‐stress coefficients with the third‐order elastic constants. Therefore, the fractional changes in the phase velocity hardly relate to the sensitivity coefficient without the third‐order elastic constant. In addition, computational results show that the point of dispersion curve crossover is affected by the borehole pressurization because of the change of velocity dispersion by borehole pressurization increasing with frequency, and as the borehole pressurization increases the velocity of the crossover point increases while the frequency of the point is unchanged.

Acoustoelastic effects on mode waves in a fluid-filled pressurized borehole in triaxially stressed formations

“…Subsequently, Winkler et al [5] proved both by theory and experiments that the intersection of the flexural wave dispersion curves can be used as an indicator of stress-induced anisotropy. Recently, applying the nonlinear acoustoelasticity model, Cao et al [6,7] derived the eigenfrequency variation formula of the mode wave considering the biaxial horizontal terrestrial stresses and borehole fluid pressure jointly. They calculated the case only considering the uniaxial horizontal terrestrial stress and borehole pressure, but they did not study the effect of biaxial horizontal terrestrial stresses.…”

Acoustoelastic effects of Stoneley waves in a borehole surrounded by a transversely isotropic elastic solid

“…1,2 An alternative approach that has been successfully applied to the estimation of stress is based on the acoustoelastic theory. 6,[9][10][11][12][13][14] The acoustoelastic effect, i.e., the velocity change of the acoustic waves in the presence of stresses, has been investigated for more than about sixty years. 15 The acoustoelastic effect is not new to rock physicists, having already been applied in various contexts such as underground mines, 16 laboratory experiments, [17][18][19][20] and boreholes.…”

“…15 The acoustoelastic effect is not new to rock physicists, having already been applied in various contexts such as underground mines, 16 laboratory experiments, [17][18][19][20] and boreholes. 6,[9][10][11][12] A nondestructive technique based on borehole cross-dipole acoustic measurements and acoustoelastic effect has been used to measure the stress magnitudes present in the earth. 6,[9][10][11][12][13][14]21 Most attempts from sonic logging assumed that the background formation is isotropic in the absence of stress.…”

“…6,[9][10][11][12] A nondestructive technique based on borehole cross-dipole acoustic measurements and acoustoelastic effect has been used to measure the stress magnitudes present in the earth. 6,[9][10][11][12][13][14]21 Most attempts from sonic logging assumed that the background formation is isotropic in the absence of stress. 6,[9][10][11][12][13][14]22 However, some rocks can exhibit anisotropy even in the absence of stress.…”

“…6,[9][10][11][12][13][14]21 Most attempts from sonic logging assumed that the background formation is isotropic in the absence of stress. 6,[9][10][11][12][13][14]22 However, some rocks can exhibit anisotropy even in the absence of stress. 23 In petroleum seismology, we often encounter one of two types of anisotropy: transverse isotropy.…”