Proving the Applicability of the Petrophysical Model Describing Acoustic Hysteresis of P and S Wave Velocities

Due to the increasing demand for hydrocarbons and the depletion of the known hydrocarbon fields there is a growing claim to predict rock physical parameters more accurate at non-conventional conditions also. It is well known that acoustic velocity in rocks strongly depends on pressure which influences the mechanical, transport and elastic properties of rocks as well as wave propagation under pressure is very nonlinear and the quasistatic elastic properties of rocks are hysteretic. Characterization of hysteretic behavior is important for mechanical understanding of reservoirs during depletion. Therefore a quantitative model - which provides the physical explanation - of the mechanism of pressure dependence is required. In this paper a petrophysical model is presented which provides the connection between the propagation velocity of acoustic waves (both P and S) and rock pressure both in case of pressurization and depressurization phases as well as explains the mechanism of acoustic hysteresis. The developed model is based on the idea that the pores in rocks close under loading and reopen during unloading. The model was applied with success to acoustic P and S wave velocity data sets.