Kun Sang Lee

Numerical Modeling on the Performance of Aquifer Thermal Energy Storage System under Cyclic Flow Regime

Coupled hydrogeological-thermal model for simulating the thermal energy storage system in aquifer is described. It is essential to provide an optimized configuration and operation schedule for wells on the site. This paper presents numerical investigations and thermohydraulic evaluation of two-well models of aquifer thermal energy storage (ATES) system operating under cyclic flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the thermal energy storage system in the aquifer. The model includes the effects of convection and conduction heat transfer, heat loss to the adjacent confining strata, and hydraulic anisotropy. The operation scenario consists of cyclic injection and recovery from two wells and four periods per year to simulate the seasonal temperature conditions. The model has been used to study performances under various operational and geometrical parameters of the storage system. The calculated temperatures at the producing well were relatively constant within a certain range through the year and fluctuating quarterly a year. Operation schedules, injection temperature, injection/production rate, and geometrical configuration of well and aquifer used in the model are shown to impact the predicted temperature profiles at each stage and the recovery water temperature. But aquifer thickness and hydraulic anisotropy have a minimal effect on the performance of ATES systems.

Aquifer Thermal Energy Storage

In general, groundwater temperatures remain relatively stable at temperatures typically 1–2 °C higher than local mean annual temperatures between depths of 10–20 m. Below these depths, groundwater temperatures gradually increase at a rate of geothermal gradient. As a result, in areas where a supply of groundwater is readily available from an aquifer, a reliable source of low temperature geothermal energy exists.

Modeling on the Performance of Standing Column Wells During Continuous Operation Under Regional Groundwater Flow

Coupled hydrogeological–thermal simulation of the standing column well (SCW) system is essential to provide an optimized configuration and operation schedule for boreholes on the site. This paper presents numerical investigations and thermohydraulic evaluation of SCW system operating under continuous flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the heat exchange in the ground. The model includes the effects of convection and conduction heat transfer, heat loss to the adjacent confining strata, and hydraulic anisotropy. The operation scenario consists of continuous injection and recovery, and four periods per year to simulate the seasonal temperature conditions. For different parameters of the system, performances have been evaluated in terms of variations in the recovery temperature. The calculated temperatures at the producing pipe were relatively constant within a certain range through the year and fluctuating quarterly a year. Pipe-to-pipe distance, injection/production rate, ground thickness, and permeability considered in the model are shown to impact the predicted temperature profiles at each stage and the recovery water temperature. The influence of pressure gradient, which determines the direction and velocity of regional groundwater flow, is also substantial.

Numerical Simulation on the Continuous Operation of an Aquifer Thermal Energy Storage System Under Regional Groundwater Flow

Abstract A three-dimensional numerical model for groundwater flow and heat transport is used to analyze an aquifer thermal energy storage system operating under a continuous flow regime. This study emphasizes the influence of regional groundwater flow on the performance of the system under various operation scenarios. The pressure gradient across the system, which determines the direction and velocity of regional groundwater flow, has a substantial influence on the aquifer thermal storage. Injection/production rate and geometrical size of the aquifer used in the model also impact the predicted temperature distribution at each stage and the recovery water temperature. The hydrogeological-thermal simulation is shown to be an integral part in the prediction of performance for a process as complicated as aquifer thermal energy storage systems.

Simulation of Aquifer Thermal Energy Storage System under Continuous Flow Regime Using Two-well Model

Abstract Large-scale thermal energy storage can be accomplished in the aquifer through the installation of an array of vertical boreholes. Coupled hydrogeological-thermal simulation of the storage system is essential to provide an optimized configuration and operation schedule for wells on the site. This paper presents numerical investigations and thermohydraulic evaluation of two-well models of aquifer thermal energy storage system operating under continuous flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the thermal energy storage in the aquifer. The model includes the effects of convection and conduction heat transfer, heat loss to the adjacent confining strata, and hydraulic anisotropy. The operation scenario consists of continuous injection and recovery from two wells and four periods per year to simulate the seasonal temperature conditions. For different parameters of the system, performances were compared in terms of normalized energy storage. The calculated temperatures at the producing well were relatively constant within a certain range through the year and fluctuating quarterly a year. Operation schedules, injection temperature, injection/production rate, and geometrical configuration of the well and aquifer used in the model are shown to impact the predicted temperature profiles at each stage and the recovery water temperature. But aquifer thickness and hydraulic anisotropy have a minimal effect on the performance of aquifer thermal energy storage systems.

Effects of hysteresis ink-S-p relationships on the performance of minewaste soil covers

Soil covers are widely used in mine waste and landfill applications to protect the environment. The finite-element based model was used to simulate the vertical flow of water through unsaturated cover soils. A hysteretic model for two-phase permeability-saturation-pressure (k-S-p) relations is implemented in unsaturated flow model to predict temporal and spatial fluid distributions in a soil cover. A representation of hysteretic soil hydraulic properties is based on a combination of van Genutchen’s equation and statistical model for relative permeability. Predictions ofk-S-p relations along major flow paths are presented for fine sand, silt, and coarse sand. Employing hysteretic and nonhysteretic relationships, this study also presents a comparison of saturation profiles in four different cover soils: fine sand, silt, and coarse sand as single covers and multi-layered soils. A number of simulations were performed to analyze the saturation profile in the cover soils subject to downward drainage due to gravity and infiltration under various conditions of at the top and bottom. The numerical results indicate that simulation of water flow involving saturation path reversals may produce significant differences between hysteretic and nonhysteretic results. Considerations should be given to effects of hysteresis in hydraulic properties to accurately predict fluid distributions in a cover soil.

Borehole Thermal Energy Storage

If it is impossible to exploit a suitable aquifer for energy storage, a borehole thermal energy storage system (BTES) can be considered. Vertical ground heat exchangers (GHE), also called borehole heat exchangers (BHE) are widely used when there is a need to install sufficient heat exchange capacity under a confined surface area such as where the Earth is rocky close to the surface, or minimum disruption of the landscape is desired.

Application of Horizontal Wells to Improve Injectivity During Polymer Flood Processes

Abstract This numerical study was undertaken to investigate and compare the performances of polymer flood processes through horizontal or vertical wells. To achieve the objective, the author performed an extensive numerical simulation for 3 different well configurations under polymer flood followed by waterflood. The potential for a horizontal well application was assessed through different scenarios in combinations of injection and production wells and reservoir geometry. Other parameters included the length and spacing of horizontal injectors and horizontal or vertical producers. For different parameters of the system, performances were compared in terms of cumulative recovery and water-oil ratio at the production well and pressure drop or injectivity at the injection well. Results demonstrate that additional oil can be recovered and injectivity was significantly improved by utilizing a combination of horizontal wells when the same volume of fluid is injected into the reservoir. The improvement of injectivity through a horizontal injection well was higher when it was combined with a horizontal producer. Parameters such as reservoir thickness, well spacing, and well length are also shown to impact the predicted injectivity. Improvement in injectivity is obtained for thicker and larger reservoirs and longer horizontal wells.

Effects of Polymer Adsorption on the Oil Recovery during Polymer Flooding Processes

Abstract The influence of water-soluble polymer adsorption on the flow behavior and oil recovery was investigated. This article presents results from an extensive numerical simulation performed for a two-well model in a five-spot pattern operating under polymer flood followed by waterflood. For different systems of adsorption parameters, slug sizes, and reservoir properties performances were compared in terms of cumulative recovery and water–oil ratio (WOR) at the production well. Properties of polymers and reservoir rocks such as adsorption parameters and vertical permeability heterogeneity are shown to impact the predicted recovery. Improvement in oil recovery and reduction in WOR was obtained for smaller values of adsorption parameters. Polymer flood in reservoirs with a severe permeability contrast between horizontal strata leads to lower volumetric sweep efficiency and displacement efficiency. The size of the polymer bank also affects the predicted recovery.

Performance of a Two-Phase Carbon Dioxide-Filled Thermosyphon

In order to utilize low enthalpy geothermal heat sources, a thermosyphon is a good device which can extract heat without using electric power. The heat transfer in the thermosyphon occurs through the circulation of a working fluid through a sequence of evaporation, vapor transfer, condensation, and liquid return. A two-phase thermosyphon system using carbon dioxide (CO2) as a working fluid has been investigated both experimentally as well as theoretically. Carbon dioxide is the only non-flammable and non-toxic fluid that has the potential to offer environmental safety in a system. A copper tube thermosyphon of total length of 1,000 mm with inside and outside diameters of 9.9 mm and 12.7 mm was developed by consisting of evaporator and condenser sections. The temperature distribution along the thermosyphon was monitored and theninput heat to evaporator section and output heat from condenser were measured as well. The effects of temperature difference between evaporator and condenser section and coolant mass flow rates on the performance of the thermosyphon were determined. The results indicate that the heat flux transferred increased with increasing coolant mass flow rate and temperature difference between evaporation and condenser section. The experimental analysis of the thermosyphon system confirms that the proposed system must be a reliable and highly efficient as well as environmentally friendly alternative to common ground-coupled systems.