New Results in Modeling the Phenomenon of Acoustic Hysteresis

Interpretation of seismic data is significantly constrained by the extrapolation of measured acoustic properties - in laboratory - of rocks in a given physical (pressure) environment. To reasonably interpret laboratory measurements, a quantitative model - which provides the physical explanation - of the mechanism of pressure dependence is required. It is well known that the change of acoustic wave velocity propagating in rocks is nonlinear with respect to pressure and the quasistatic elastic properties of rocks are hysteretic. In this paper a petrophysical model is presented which provides the connection between the propagation velocity of acoustic wave and rock pressures both in case of pressurization and depressurization cycles. The developed model also describes well and explains the mechanism of acoustic hysteresis. The model is based on the idea that the microcracks in rocks close during pressurization and reopen during depressurization. The model was applied to acoustic P wave velocity data sets. Measurements were carried out at various incremental pressures and the parameters of the petrophysical model were determined by a linearized inversion method. The calculated data matched accurately with measured data proving that the new rock physical model describing acoustic hysteresis applies well in practice.