Estimating Mineral Scaling and Porosity Alterations During the Circulation Test at Utah-FORGE Site Using Reactive Transport Modeling

Abstract

The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) field-scale laboratory was created to promote and expedite the development of Enhanced Geothermal System (EGS) resources. This paper aims to enhance the understanding of the thermal-hydrological-chemical (THC) processes involved with EGS operation at the FORGE site. The primary objective is to evaluate the mineralogical changes and their impact on porosity and flow, using chemical speciation data from injected and produced water collected during the circulation test at the deepest well, located at 9,500 feet. Leveraging reservoir and geochemistry data, a 3-dimensional THC model was created to investigate water-rock interactions and flow in porous and fractured media using the FALCON (Fracturing And Liquid CONvection) code and The Geochemist’s Workbench. The model's results forecasted the spatial and temporal distribution of dissolved and precipitated minerals and the net changes in porosity due to reactive geochemistry temperature variations during the circulation test. Mineralogical changes were more significant in the fracture network compared to the rock matrix, owing to the preferential flow associated with higher permeability of fractures. Additionally, calcite precipitation was dominant among the minerals, with mica precipitation also observed along the fractured plane near the injection well. The spatial distribution of precipitated minerals indicated how fluid transport in the wells moves these minerals further away along the fractured planes. The model predictions, such as pH and aqueous species, were consistent with the produced water data. The results of this study will aid in the development of EGS resources and suggest mitigation and operational strategies for sustainable geothermal production.