Estimation of the effective thermal properties of cracked rocks

Abstract

In geo-engineering applications, the effective thermal properties (ETPs) of cracked rock are strongly dependent on the configuration of the cracks and the thermal properties of the saturating fluid, which differs from that of the rock matrix. In this study, methods for predicting the ETPs of cracked rock are investigated. The effects of various factors such as the crack distribution, the type of saturating fluid and the applied stress on the ETPs are analysed. Formulas for the effective thermal conductivity (ETC) and the effective thermal expansion (ETE) are developed in a discrete form based on the homogenisation method, where the interactions of the cracks in different directions are neglected. To analyse the effects of the crack distribution and the type of saturating fluid on the ETC and the ETE, an example of saturated rock with one family of cracks is considered. The results reveal that the crack distribution has a significant anisotropic effect on both the ETC and the ETE. The difference in the bulk moduli of the rock matrix and the fluid in the cracks also has an important effect on the ETE. The behaviour of the ETC and the ETE of granite at various levels of stress is analysed with triaxial compression tests. The growth of microcracks induced by the applied stresses causes significant anisotropy in both the ETC and the ETE. This study provides insight into the factors that affect the ETC and the ETE and methods to estimate the ETC and the ETE of cracked rock in geo-engineering applications.

Keywords:

• effective thermal conductivity
• effective thermal expansion
• cracked rocks
• discrete method
• geo-engineering applications

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the National Science Foundation of China [grant number 51479193] [grant number 51209085]; “100 Talent Program” of the Chinese Academy of Sciences.