Enhanced Geothermal Systems Modeling and Optimization Workflows for Power Production from Geothermal Reservoirs

Abstract The purpose of this project is to demonstrate the value of modeling enhanced geothermal systems (EGS) and to identify specific aspects of the modeling process that are unique and critical to ensuring the accuracy of EGS model construction. An accurate model enables EGS design optimization so that geothermal energy from high enthalpy wells reach their full potential and increase their competitiveness to current and future energy sources. A mechanical earth model (MEM) is created to describe static subsurface conditions. Hydraulic fracture geometries are modeled for two stacked injector-producer wells. Propped and unpropped simulated hydraulic fractures are calibrated with microseismic data, fiber optic measurements, and fracture pressure history matching observations from the field. The calibrated static model is used for flow simulation through the injector-producer pair. History matching will leverage observed production rates and their corresponding fluid temperatures to refine reservoir characterization and enhance predictive accuracy. This model is then used for power production forecasting, sensitivity analysis, and the optimization of geothermal reservoir management. Modeling an EGS system revealed the necessity of characterizing (seismic and sub-seismic) natural fracture networks that act as additional planes of weakness and guide hydraulic fracture growth. This additional fracture complexity provides the required surface area to the geothermal reservoir needed to exchange enthalpy from the granitic rock to the circulated water, which has seen up to 144°C in temperature increase after completing the subsurface circulation. A crucial step in the modeling process involved developing a thermal reservoir simulation case with imposed isothermal boundary conditions that assisted in accurately matching observed produced fluid temperatures by providing a stable heat flux from the reservoir. The accurate matching of the hydraulic fractures was enabled by the presence of calibration data such as fiber optic and microseismic that helped to identify the number and location of intersections between the wells. Corrections were made to the MEM to match the instantaneous shut-in pressure (ISIP) observations at each stage. High temperature (175°C to 225°C) was likely responsible for higher-than-expected principal stresses. The circulation tests were successfully matched to reveal high confidence in the subsurface model. The workflow is executed on the Utah FORGE dataset and adds to the existing literature published by the University of Utah by discussing the process of creating a fully calibrated model for EGS that integrates a thermal model into a reservoir simulation case using a commercial software. It also goes a step further to provide estimates of power production through a sensitivity analysis and explores the opportunity to maximize the commercial viability of such projects.