Investigating the Effect of Thermal Conductivity on Geothermal Energy Production at Different Circulation Rates in an EGS Abandoned Case Study

Abstract

The thermal conductivity coefficient of the reservoir formation rock-cement-casing combination is an important parameter affecting the optimum circulation flow rate in open and closed-loop systems. Despite its importance, an accurate value of the thermal conductivity may not used in modeling due to the fact that either the thermal conductivity of the rock and cement is not measured in the lab to be accurately known, or the effect of cement and casing thermal conductivities on the net thermal conductivity is ignored. Therefore, this work investigates the effect of a change in the thermal conductivity on the net heat energy, the net power and the coefficient of performance (COP), at different circulation rates. The simulation results using CMG software for a high reservoir temperature shallow case study in Trindad and Tobago show that when the net thermal conductivity of 2 W/m/K is doubled, the net heat energy and power show minimal increase of up to ~1%. Such minimal increases are the case at all circulation rates, with the greatest heat increase occurring at the largest circulation rate. The minimal produced heat increase is attributed to the assumption of external reservoir temperature being at the nearest radius to the wellbore wall due to the fact that the high thermal conductivity of water in the fractures dominates and the fractures extend so far that the surface area for heat flow is very high. This is in accordance with previous research simulation results.