Assessing the Effect of Realistic Reservoir Features on the Performance of Sedimentary Geothermal Systems
Abstract：
The technical feasibility of commercial geothermal production from sedimentary reservoirs is being studied using numerical reservoir modeling. This study considers sedimentary rock formations with relatively low permeability, with the purpose of expanding the current geothermal energy resources toward new regions. A numerical reservoir model, previously validated against an analytical model, is modified removing the analytical model assumptions to include more realistic behavior of fluids and reservoir rock. The performance of the sedimentary geothermal system is evaluated in terms of the hydraulic behavior (i.e., well productivity/injectivity), and thermal evolution of the reservoir (i.e., thermal breakthrough time). Here we present how changes of reservoir rock and water properties, as function of pressure and temperature, affect the performance of the sedimentary geothermal system. Particularly, water density and viscosity, and rock heat capacity play a significant role in geothermal reservoir performance. Also, the effects of heterogeneity and anisotropy of rock properties are evaluated using reservoir simulation models with spatially varying porosity and permeability. Premature thermal breakthrough is observed in cases where a high permeability streak is considered in the reservoir model. The dual permeability concept is applied to the reservoir model to study the performance of the sedimentary geothermal system considering networks of natural fractures. The parameters used to modify the behavior of the fracture network are the fracture conductivity and shape factor. The results showthat a balance between hydraulic and thermal performance should be achieved to meet the target flow rate while also ensuring reservoir sustainability over the expected 30 year lifetime of the geothermal power plant. Therefore, sedimentary geothermal systems should be engineered to secure producing performance and operational sustainability simultaneously.
