Parametric analysis of geothermal reservoir performance in Mesozoic sandstone formations within the North German Basin developed by multi-well systems

Abstract

In the context of the heat transition in Germany, the decarbonization of the heating and cooling industry via renewable energy sources requires the usage of comprehensive strategies and novel engineering solutions. With regard to district heating in urban areas, middle-deep geothermal resources offer a great potential which has not been fully utilized yet due to the required minimum temperature of district heating networks, leading to the additional employment of industrial and high-capacity-power heat pumps. However, the controlling factors on the optimal and sustainable development of those middle-deep geothermal resources are not fully elucidated yet. By evaluating numerical approaches against analytical model solutions, this work systematically analyzes the impact of reservoir quality and operational controlling factors on the performance of Mesozoic sandstone reservoirs in the North German Basin (NGB) targeted by multi-well arrangements. For the first time, we compare in a comprehensive manner previous analytical model results with our numerical findings to characterize more broadly the quantitative influence of different controlling factors on the thermal breakthrough occurrence time, the maximum cooling rate after the occurrence of the thermal breakthrough and the end production temperature. Moreover, we especially focus and illustrate the controls on the behavior of the production temperature after the thermal breakthrough has occurred and conduct a one-factor-at-a-time (OAT) parametric sweep analysis with regard to the thermal utilization time or life span of a geothermal facility. Based on our numerical results, we set up a ranking scheme showing the influence of varying controlling parameters on the considered performance parameters. One of the striking findings of our scenario analysis relates to the thermal breakthrough occurrence time, which is 17 ± 3% higher for a geothermal doublet array compared to a single doublet. Yet, the maximum cooling rate of the production temperature after the thermal breakthrough is higher for the array layout, depending on the number of neighboring injection wells. Our comprehensive numerical study, therefore, illustrates in detail the complex thermo-hydraulic interaction of geothermal doublet arrays, the controls on the defined thermal lifetime as well as the optimization possibilities of middle-deep geothermal resources.