Experimental verification of the physical nature of velocity-stress relationship for isotropic porous rocks

Abstract

The exponential increase of seismic velocities with effective stress has usually been explained by the presence of pores with a broad distribution of aspect ratios. More recently, a stress-related closure of soft pores with a narrow distribution of compliances (e.g., grain contacts) has been suggested to be sufficient to explain such exponential stress dependency. This theoretical interpretation has been verified here using laboratory measurements on dry sandstones. On the basis of these experimental data, linear dependency of elastic compressibility on soft porosity and exponential decay of soft porosity and elastic compressibility with effective stress up to 60 MPa is confirmed. Soft porosity, estimated from the fitting coefficients of elastic compressibilities, is on the same order of magnitude but slightly lower than obtained from strain measurements. The results confirm applicability of previously proposed stress sensitivity models and provide justification for using this approach to model stress dependency of elastic properties for isotropic and anisotropic rocks.