On the role of rock matrix to heat transfer in a fracture-rock matrix system
Abstract
Geothermal energy is a clean, stable, and sustainable energy source, and the study of thermal energy transfer processes in the subsurface fractured media is important to improve thermal energy recovery performance in enhanced geothermal systems (EGS). The analytical models provide a robust and easy-to-use tool to investigate the thermal transfer mechanisms and assess the long-term heat distribution. In this study, a fully coupled analytical model is developed for thermal energy transfer in a single fracture-rock matrix system where the coupling implies that the governing equations of thermal transfer in the fracture and rock matrix relate to two continuity conditions: temperature and thermal flux are continuous at the interfaces of the fracture-rock matrix. The newly proposed model accounts for thermal convection, longitudinal thermal conduction and thermal dispersion in the fracture, and transverse thermal conduction in the rock matrix. The mathematical model is established accordingly for such a fully coupled two-dimensional problem. With the numerical Laplace inverse transform technique, the semi-analytical solutions are obtained to investigate the thermal energy transfer processes and assess the spatiotemporal temperature distribution in the fracture and rock matrix system. The solutions are then extensively validated against existing studies and proven to be accurate and robust. The present study demonstrates that: 1) thermal dispersion in the fracture has moderate influence on the temperature distribution in the fracture and rock matrix domains, and longitudinal thermal conduction in the fracture has minor effects on the temperature distribution in the system; 2) transverse thermal conduction in the rock matrix is a critical parameter that determines the spatiotemporal temperature distribution in both the fracture and the rock matrix domains. Ignoring thermal conduction in the rock matrix will lead to significant overestimation of temperature in the short and long terms; 3) the sensitivity analysis implies that thermal dispersivity in the fracture has great influence on heat transfer in the system and strong interaction effects with other variables, and the thermal property of rock matrix also plays a key role in heat transfer in the fracture-rock matrix system.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMMR55B0018Z