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Predicting Mineralogical Changes and Porosity Alterations in EGS Reservoirs: Insights from Reactive Transport Modeling at the FORGE Site
Ram KUMAR, Lynn B. MUNDAY, Stuart SIMMONS, Clay JONES, Ming YANG, Ghanshyam NEUPANE, Robert SMITH, Rachael COLLDEWEIH, Travis MCLING, Robert PODGORNEY
[Idaho National Laboratory, USA]
The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) field-scale laboratory was established to advance the development of Enhanced Geothermal System (EGS) resources. This paper aims to predict the mineralogical changes and hydraulic conductivity in the fractured networks using the chemical composition of injected and produced water in wells 16A and 16B during the circulation test conducted between August and September 2024 at the FORGE site. The primary objective is to provide insights into the impact of geochemistry on porosity and flow during the planned long-duration circulation test. A thermal-hydrological-chemical (THC) model was developed using injections and produced water data to explore water-rock interactions and flow in porous and fractured media, using the FALCON (Fracturing And Liquid CONvection) code and The Geochemist’s Workbench. The fracture domain and water chemistry have been updated based on the latest geophysical and geochemical data from the previous circulation tests in August-September 2024. The model's results predicted the mineralogical changes and the net changes in porosity due to water-rock interaction and temperature variations for 6 months to inform the next long-duration circulation test. The geochemical model, calibrated using produced water data from previous tests, predicted the dissolution of quartz and retrograde precipitation of carbonate minerals. In this simulation, production of CO2 has been considered based on the characteristics of produced water and gas samples. The mineralogical changes vary in the fractured network, indicating how fluid transport in the wells influences the movement of precipitated or dissolved minerals along the fractured plane. Model predictions, such as pH, mineral saturations, and concentration of aqueous species were consistent with the produced water chemistry reported during previous circulation tests. The results of this study will aid in planning future long-duration circulation tests and the development of EGS resources for sustainable geothermal production.
Topic: FORGE