Effect of reservoir’s permeability and porosity on the performance of cellular development model for enhanced geothermal system

Abstract

A fully coupled thermo-hydro-mechanical cellular development model is established to simulate the heat production in the artificial fractured geothermal reservoir. Influences of different coupling models on the evaluation result were investigated. The production performance of the cellular EGS model was studied, such as production temperature, heat extraction ratio, flow impedance and output thermal power. The reliability of the numerical model based on the local thermal equilibrium theory is verified by the Lauwerier’s solution and Bai’s solution from the view of thermal-hydraulic (TH) and thermo-hydro-mechanical (THM). Besides, the degree of grid refinement is deduced by the grid convergence index (GCI) method. The results show that the production capacity can be overestimated by 13.06% when without considering the variation of permeability and porosity of the rock matrix over a 40-years of operation. The anisotropic permeability of thermal reservoir is another important factor that affects the results of assessment. The production temperature of anisotropic model is less than that of isotropic model. Model 2 has a stronger advantage over the traditional doublet system (Model 1). And the high efficiency time of Model 2 account for 46% of the total operation time, which 1.59 times as long as Model 1 and 2 times as long as Model 3. Furthermore, Model 2 is affected greatly by the injection flow rate, elastic modulus and reservoir permeability. When the elastic modulus of thermal reservoir is more than 35 GPa, the performance of cellular development model will be greatly reduced. Model 2 can earn its commendation when H = 340 m, M = 30 kg/s, E = 30 GPa and N = 4. Those results can provide the significant guidance of development plan and coupling methods for enhanced geothermal system.