Impact of coupling terms on the thermal transport mechanism in a fracture matrix coupled system

Understanding the heat transfer mechanism in the subsurface is essential for designing geothermal heat extraction system as well as oil extraction system in petroleum reservoirs. Due to the inherent variability in thermal diffusivity in the rock matrix–fracture system, this interface can either act as a source or sink for temperature. The main objective of this study is to investigate the influence of considering the heat transfer term either as a source or a sink at the fissure–matrix interface while describing the spatial and temporal distribution of temperature in a fractured reservoir at the scale of a single fissure. A numerical model is developed using implicit finite difference method to forecast the spatial and temporal propagation of the thermal front and to analyse the sensitivity of various coupling terms at the fissure–matrix interface. Following the numerical treatment, the velocity of thermal front as well as the degree of thermal dispersion encountered within the high-permeable fissure was computed using the method of spatial moments (first and second, respectively). Numerical results indicate that the mobile fluids within the fissure could reflect the exchange of stored heat energy from the rock-matrix quite efficiently for the cases with the heat gain term in the fissure equation. An enhanced mixing effect was observed for the cases having an explicit heat loss term for the matrix in the absence of any source/sink in the fissure equation. However, the thermal mixing regime remained insignificant for the cases having an explicit heat gain term in the fissure.