The impact of aquifer heterogeneity on the performance of aquifer thermal energy storage

Abstract

[1] Heterogeneity in hydraulic properties of the subsurface is not accounted for in current design calculations of aquifer thermal energy storage (ATES). However, the subsurface is heterogeneous and thus affects the heat distribution around ATES wells. In this paper, the influence of heterogeneity on the performance of a doublet well system is quantified using stochastic heat transport modeling. The results show that on average, thermal recovery decreases with increasing heterogeneity, expressed as the lognormal standard deviation of the hydraulic conductivity field around the doublet. Furthermore, heterogeneity at the scale of a doublet ATES system introduces an uncertainty in the amount of expected thermal interference between the warm and cold storage. This results in an uncertainty in thermal recovery that also increases with heterogeneity and decreases with increasing distance between ATES wells. The uncertainty in thermal balance due to heterogeneity can reach values near 50 percent points in case of regional groundwater flow in excess of 200 m/yr. To account for heterogeneity whilst using homogeneous models, an attempt was made to express the effect of heterogeneity by an apparent macrodispersivity. As expected, apparent macrodispersivity increases with increasing heterogeneity. However, it also depends on well-to-well distance and regional groundwater velocity. Again, the uncertainty in thermal recovery is reflected in a range in the apparent macrodispersivity values. Considering the increasing density of ATES systems, we conclude that thermal interference limits the number of ATES systems that can be implemented in a specific area, and the uncertainty in the hydraulic conductivity field related to heterogeneity should be accounted for when optimizing well-to-well distances.Citation: Sommer, W., J. Valstar, P. van Gaans, T. Grotenhuis, and H. Rijnaarts (2013), The impact of aquifer heterogeneity on the performance of aquifer thermal energy storage, Water Resour. Res., 49,[8128][8129][8130][8131][8132][8133][8134][8135][8136][8137][8138]

Analysis of the impact of storage conditions on the thermal recovery efficiency of low-temperature ATES systems

“…As a consequence of heterogeneity the A/V-ratio in practice is higher compared to the expected value for a homogeneous aquifer. Although they both use a single ATES configuration, Sommer et al (2013) and Caljé (2010) show that the net effect of heterogeneity on efficiency is limited over multiple storage cycles and its influence is much smaller compared to the effect of A/V and ambient groundwater flow on the efficiency. Only when gravel layers are present such heterogeneity may affect efficiency significantly, and should therefore best be blinded (Caljé, 2010).…”

Optimization and spatial pattern of large-scale aquifer thermal energy storage

“…Numerical modeling of a doublet ATES system shows that thermal recovery in a stagnant aquifer can be higher than 75% and drop to 40% with a regional groundwater flow velocity of 150 m/y [15]. Field studies report thermal recovery values between 65% and 82% [16,17].…”

“…However, because of thermal interference the performance of individual wells can decrease. Previous studies have shown the effect of well distance on thermal interference for doublet systems by scaling the well distance with the thermal radius [15,19]. The thermal radius (R th ) of an ATES well is defined as the maximum distance of the thermal front from the injection well in a homogeneous medium, neglecting vertical flow, advection by regional flow, thermal conduction and dispersion.…”

“…Here, c w and c a are the volumetric heat capacity of water and the aquifer (groundwater and aquifer matrix) respectively, V is the volume of water that is injected in one storage cycle and H is the length of the well screen [15]. From numerical modeling studies, Kim et al [19] report that the recovery of thermal energy is not significantly affected when the wells are separated by more than one thermal radius, while Sommer et al [15] show that in both homogeneous as heterogeneous aquifers the thermal recovery decreases for well distances below 2 thermal radii.…”

“…From numerical modeling studies, Kim et al [19] report that the recovery of thermal energy is not significantly affected when the wells are separated by more than one thermal radius, while Sommer et al [15] show that in both homogeneous as heterogeneous aquifers the thermal recovery decreases for well distances below 2 thermal radii. The different conclusions from these studies can partly be attributed to the dependency of thermal recovery on other aspects than the (scaled) distance between the wells, such as the volume of storage and hydrological and thermal conditions, but also by the lack of a well-defined criterion by which thermal interference should be evaluated.…”