The differential characteristics of temperature- and pressure-dependent dynamic and static elastic properties are investigated in a range of temperature and confining pressure for porous sandstone. Results show that the dynamic and static Young's moduli increase against confining pressure, whereas the dynamic one decreases and the static one increases against temperature, respectively. The ratios of static and dynamic elastic properties for the Young's modulus decrease against the ratio of thermal stress to confining pressure. The opposite result is observed for the Poisson's ratio. We demonstrate that the progressive crack closure of primary microcracks associated with the limited expansion of cement material is dominant in the range of experimental pressure and temperature, instead of the development of new microcracks during thermal treatments. Therefore, the axial and radial strains decrease with increasing pressure and temperature, which reduces the static Poisson's ratio but increases the static Young's modulus.
Knowledge the elastic properties of rocks is essential in the characterization of the mechanical properties (Batzle et al. 2006). Elastic properties from slow deformation of a rock are typically determined from stress and strain data, referred to as the static elastic properties, while requires access to the rock mass, which is expensive and time consuming. Elastic properties can also be calculated from elastic wave velocity. Inversion of these data gives the dynamic elastic properties. However, the dynamic and static elastic properties are generally not equal and consequently, for the purposes of subsurface geomechanical modeling and petroleum reservoir geomechanics (Cheng & Johnston 1981), the differences between the dynamic and static elastic properties should be understood.
Although many works deal with the effect of temperature or pressure on the dynamic and static moduli in porous rocks (e.g. Winkler et al. 1979; Fjær 2009; Zhang et al. 2019), the joint effects of temperature and pressure remains largely unaddressed. This study elaborates the differential characteristics between static and dynamic moduli induced by the joint effects of temperature and pressure for porous sandstone. We demonstrate that temperature and pressure significantly affect the microstructure evolution of porous rocks, which in turn affects the static and dynamic moduli.
