Sensible energy storage in aquifers: 1. Theoretical study

Abstract

This paper presents the results of a theoretical study on the thermal behavior of a hot water storage system in an aquifer using a single well. It is shown that the storage efficiency and temperature are controlled by a limited number of dimensionless groups that depend on the aquifer's physical characteristics and the storage operating parameters. A numerical model is checked against analytical solutions and is then used to evaluate the variation with time of the well temperature during production periods for symmetrical cycles (production volume and flowrate equal to injection volume and flowrate). From these results, type curves are plotted for several sets of dimensionless parameters, covering the range of practical applications. Effects of unequal injection and production periods, standby periods, and other operating conditions are also investigated. Practical recommendations are made for efficient storage projects. INTRODUCTIONThe depletion of classical resources in fossil fuels combined with high inflation rates has recently enhanced interest in developing the exploitation of alternate energy sources and in improving efficiency in the use of energy in general. Along these lines, hot water storage in permeable geological layers appears particularly attractive, for it provides a way of transferring energy from a period of low consumption where it is being produced, into peak hours or seasons.The most important parameters in a heat storage project are (1) the recovery factor (i.e., the ratio of the quantity of energy recovered to that injected) which determines the project economic feasibility and (2) the energy (or temperature) level in the recovered water and its variation during production, which conditions the type of surface utilization. These parameters depend upon the storage physical characteristics (aquifer reservoir thickness, thermal conductivity, heat capacity, etc.) and operating conditions (production and injection rates, duration of injection and production cycles, etc.).In order to facilitate rapid technical evaluations of heat storage projects, and to assess their economic feasibility without engaging into heavy investments, a general study was undertaken of the various parameters that would influence the behavior of such systems. The study, restricted to the case where the same borehole is used for hot water injection and production, included both a theoretical investigation and a field experiment. The theoretical results, which were used to construct type curves convenient for practical applications, are presented hereinafter. Results and analysis of the field experiment are the subject of a companion paper. ScoPE OF STUDYThe theoretical study is concerned with storage of hot water under liquid phase (sensible energy storage) in relatively deep aqufers. Compared with that in shallow aquifers,• Now with Flopetrol, 245 deep aquifer storage appears advantageous because (1) regional groundwater flow being usually negligible, the injected hot water is not displaced, (2) thickness of overburde...

Evaluating the influence of thermal dispersion on temperature plumes from geothermal systems using analytical solutions

“…This is mainly due to the fact that they are based on controlled lab experiments with homogenous porous media and the uncertainty introduced by macroscale heterogeneities of hydraulic conductivity is not accounted for. Sauty et al [32] and de Marsily [17] proposed a thermal dispersion coefficient, similar to solute transport [15], where the thermal dispersion term is related to the heterogeneity of the velocity field and is a linear function of this velocity. The following expressions are used by modelers to represent what they do not know about the exact structure of the aquifer and its heterogeneity [19,33e36]:…”

Numerical modeling of aquifer thermal energy storage system

“…Researches on analytical methods for heat transfer have been conducted by Sauty et al [18], Uffink [19], Voigt and Haefner [20], Krarti and Claridge [21], Yang and Yeh [22], and Stopa and Wojnarowski [23]. Kangas and Lund [17] pointed out that analytical solution is applicable only to the simplest cases or to qualitative estimations.…”

“…Recently, with the advance of modern computing power, three-dimensional numerical modeling become widely used such as in Dickinson et al [8], Lee [13], Tenma et al [28], and so on. The main objective of the numerical modeling for the ATES system before 1990s was to predict heat transfer in the model domain by injected water through a single well [16,18,26], and it is now widening into predicting recovery temperature by heat loss [13,16], injection depth in the aquifer [13,28], injection rate [13,28], injection time [28], and regional groundwater flow [17].…”

The use of salinity contrast for density difference compensation to improve the thermal recovery efficiency in high-temperature aquifer thermal energy storage systems

“…Although the displacement of heat and solutes by regional groundwater flow cannot be considered with the axi-symmetric approach, the regional groundwater flow is generally low in deep brackish aquifers targeted for HT-ATES systems (e.g. Sauty et al 1982). Hence, neglecting heat and solute loss by regional groundwater flow during HT-ATES is considered a reasonable assumption.…”

“…Zuurbier et al 2014). Also prolonged injection of hot water during the first cycle can be applied to reduce the temperature differences and associated heat loss in subsequent recovery cycles (Sauty et al 1982). Fig.…”