Energy capacity of a geothermal reservoir

Abstract

The effect of conductive heat transfer recharge originating from the surrounding conduction dominated geothermal system on the geothermal reservoir lifetime has been reviewed during its development, by studying the effect of multiple reservoir and production parameters. A two dimensional (2D) finite volume implicit coupling strategy, using a direct solver method, is applied on a non-isothermal lumped-parameter model to simulate reservoir development over a period of 35 years. Two test cases are investigated, modelled after the low temperature geothermal fields of Middenmeer in The Netherlands and Soultz-sous-Forêts in France. Resulting produced thermal water temperature and thermal energy flow rate profiles are simulated with and without consideration of the geothermal system. A resolution of 200×200 equidistant structured cells is applied to cover an integrated (reservoir and surrounding) domain that extends 2 km vertically and 10 km horizontally. The reservoir domain extends 200 m vertically and 1 km horizontally, covered by a computational grid resolution of 20×20. Sensitivity analysis show that this is the best resolution that can be applied without losing simulator stability and accuracy.

Results show that the conductive heat transfer recharge originating from the surrounding geothermal system has a significant effect on reservoir lifetime by reducing temperatures after thermal drawdown up to 26.5% in the first test case and up to %22.6 in the second test case. In addition, it lead to an increase in the average annual thermal energy production, up to %12.5 and %14.3 respectively. The consideration of the conductive recharge from the surrounding domain shows a significantly increased lifetime estimate for low temperature geothermal reservoirs. Furthermore, permeability, rock thermal conductivity and (re-)injection temperature are the reservoir and production parameters that can greatly influence the reservoir lifetime.