Temperature- and Pressure-Dependent Pore Microstructures Using Static and Dynamic Moduli and Their Correlation.

Temperature- and pressure-dependent elastic properties (static and dynamic shear and bulk moduli) of porous rocks are investigated in terms of the characteristics of pore microstructures (i.e., crack density, crack porosity, and crack aspect-ratio distribution). Based on the Mori–Tanaka (MT) and David–Zimmerman (DZ) models, we correlated elastic properties with these microstructural characteristics and indicated that these microstructural properties can be estimated from dynamic and static moduli that are measured by considering the joint effect of thermal stress and confining pressure. Experiments with a tight sandstone under the saturated condition show that the cumulative crack density and porosity obtained from static moduli are higher than those from dynamic moduli. We demonstrated that the MT and DZ models can be used to describe the temperature- and pressure-dependent microstructures using static and dynamic properties. The dynamic bulk compressibility and shear compliance decrease with increasing confining pressures and decreasing temperatures, whereas the corresponding static values experience complex variations due to the joint effect of thermal stress and confining pressure. For the domination of thermal stress exerted by an increase in temperature, the widening of earlier formed micro-cracks during heating reduces the static moduli. However, during the domination by confining pressure, pre-existing micro-cracks will be closed with increasing temperatures, which increases the static moduli. These static elastic properties (Young's modulus, bulk modulus, and Poisson's ratio) share a similar exponential trend with the ratio of thermal stresses to confining pressures, which can be used to correlate dynamic and static moduli. Highlights: We illustrate temperature- and pressure-dependent pore microstructures jointly using static and dynamic moduli based on the Mori-Tanaka and David-Zimmerman models. Experiments with a saturated tight sandstone show that the cumulative crack density and porosity obtained from static moduli are higher than those from dynamic moduli. Static moduli share a similar exponential trend with the ratio of thermal stresses to confining pressures based on which we propose an approach to estimate static moduli from dynamic moduli. [ABSTRACT FROM AUTHOR]