Temperature Effect on the Velocity‐Porosity Relationship in Rocks.

Understanding the effect of temperature on physical properties of rocks is important to develop deep oil, gas, and geothermal resources. Velocity‐porosity relations are essential ingredients for a seismic rock physics model. However, relatively little effort has thus far been made to capture the temperature effect on velocity‐porosity relations. To overcome this limitation, we develop a double‐porosity model based on Biot's theory. This model is complemented with the Batzle‐Wang empirical equations for the pressure and temperature dependence of the pore fluid, as well as the David‐Zimmerman model to quantify temperature‐dependent microcrack density. The combined model is tested on carbonate and hyaloclastite samples, for which the variation of ultrasonic P‐wave velocity with temperature has been measured in the laboratory. Comparison of the predicted P‐wave velocity with the measured velocity shows that the proposed model is capable of quantitatively describing the rock velocity‐temperature and velocity‐porosity relations. We found that, for our rock samples, the temperature‐dependent change of microcrack porosity was not the dominant factor affecting the velocity‐porosity relation and that the temperature‐dependent fluid properties had a greater effect. The proposed model also predicts that the velocity dispersion and the attenuation peak of P‐waves in carbonate rock samples become less pronounced with increasing temperature. Key Points: We develop a temperature‐dependent double‐porosity model for analyzing joint effects of pore fluid and microcracks on rock anelasticityModeling experimental data shows that temperature‐dependence of fluids dominates velocity‐temperature relations in rocksFor different pore fluids, there is a characteristic trend of velocity‐porosity at different temperatures [ABSTRACT FROM AUTHOR]