Abstract
The equivalent continuum method an effective approach for modeling heat transfer in fractured geothermal reservoirs. However, presently there is a lack of systematical and profound study on application conditions of the equivalent porous media (EPM) method. In this study, we numerically investigated the application conditions of the EPM method based on geological data of Yangbajing geothermal field. The results indicate that when fracture spacing is within 3–25 m, the results of the EPM method are basically in the same levels as those of the MINC method. However, when the fracture spacing is within 25–300 m, differences of the EPM method from the MINC method increase with the fracture spacing, so when the fracture spacing is within 25–300 m, it is unreasonable to adopt the EPM method to simulate the fractured reservoirs. With the fracture spacing increasing within 25–300 m, the system production temperature and electric power will gradually decrease; the injection pressure, reservoir impedance and pump power will gradually increase; and the energy efficiency will gradually decrease.
Highlights
Gelet et al used the dual porosity media (DPM) to investigate the performance characteristics of enhanced geothermal system (EGS) reservoirs under the condition of thermodynamic nonequilibrium effect, and the results demonstrate that the difference between DPM and equivalent porous media (EPM) decreases with the decrease in fracture spacing; the effect of thermodynamic nonequilibrium on the production temperature gradually decreases with the decrease in fracture spacing [18,19]
In order to investigate the influence of fracture spacing on heat conduction and convection in fractured geothermal reservoirs and determine the application conditions of the EPM method and the DPM method, in this study, we numerically investigated the application conditions of the EPM method and the DPM method with TOUGH2 codes based on the geological data from Yangbajing geothermal field
We mainly investigated the influence of the fracture spacing on the electricity generation performance and efficiency for fracturing spacing within 3–300 m by means of numerical simulation, and we discussed the applicable fracture spacing for the EPM method based on the geological data from Yangbajing geothermal field
Summary
The ECM treats the actual and discrete fracture network as an equivalent continuous porous medium, and this method is mainly used to model highly fractured systems. Because only few fracture distribution data are required and the computation efficiency is very high, ECMs have been widely used in fractured geothermal reservoir simulation, with the EPM method being most used [7,8,9,10]. The DFN method requires many fracture distribution data, and its calculation efficiency is very low; it has rarely been used, its use has recently been increasing in geothermal reservoir modeling because of the advancement of computational technology [4,5]. Though the DFN method takes more time, it usually provides more information on the response of the fracture system
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