Digital microstructure insights to phase evolution and thermal flow properties of hydrates by X-ray computed tomography

Abstract

Natural gas-hydrates are valuable energy resource with rich deposits, and their thermal transport and thermal dynamic mechanical behaviors significantly affect the long-term production process and phase change-based thermal energy storage characteristics of these energy resources. This paper aims to propose novel relations to predict the thermophysical properties, to investigate the hydrate phase evolution in microstructures, and to study the thermal transport and thermal dynamic mechanical properties. Hydrates formation experiments in sandpack samples and ultrasonic wave tests are conducted with the aid of X-ray CT imaging. Digitalization microstructures models and variables are defined to describe the hydrate phase evolution, and novel relations are proposed to accurately predict the thermophysical properties based on the microporosity and ultrasonic wave velocities. The thermal transport and thermal dynamic mechanical properties in microstructures with hydrate, water, residuary pore and grain phases are studied. Results show that the average errors of porosity, P-wave and S-wave velocities between the experimental data and computed results by the proposed relations are less than 5%, indicating the accuracy and reliability of the proposed method. The temperature fraction decreases with increasing underground temperature and decreasing hydrate saturation. The thermal stress and thermal displacement increase as temperature and hydrate saturation increase. There are strong anisotropy for the temperature fraction, thermal stress and thermal displacement during the thermal transport of hydrates.