Seismic frequency measurement of velocity and attenuation

Velocity dispersion and attenuation in rocks are coupled properties that depend on the pore fluids and fluid flow. Attenuation shows a peak at high partial gas saturation. The amplitude of this peak increases with frequency. With full saturation, velocities rise but dispersion remains approximately constant. A substantial frequency shift occurs with decreasing permeability or fluid mobility. Thus transport properties do have a measurable effect on seismic properties. These effects are dependent on confining pressure, dropping rapidly as pressure increases. For consolidated rocks, these trends are consistent with crack or ‘squirt’ flow mechanisms. These effects hold strong potential for use as a hydrocarbon indicator attribute or for time lapse (4-D) seismic monitoring.. Estimation of formation permeability may also be possible. influence (Clark, 1980; Winkler et al., 1982; Murphy, 1983; Tittmann et al., 1984; Jones, 1986; and Tutuncu et al., 1995). These results indicate that the dominant mechanism is the interaction and motion of fluid in the rock frame rather than intrinsic losses either in the frame or fluids themselves. Squirt flow is believed to be the primary loss mechanism in consolidated rocks although the inertial Biot mechanism may be important in highly permeable rocks (Vo-Thanh, 1990; Yamamato et al., 1994).