Experimental Study of the Mineral Precipitation Dynamics During Geothermal Reinjection

Abstract

The efficiency of geothermal energy extraction strongly depends on the productivity and injectivity of the wells. These are governed by porosity, permeability, fluid properties and flow conditions in the reservoir, wellbores, and surface facilities. Permeability and fluid conditions can be altered by various processes, such as mineral precipitation, fines production and migration, thermal fracturing, etc. Understanding the underlying mechanisms of such processes is essential for the optimal selection of operating conditions that ensure efficient reservoir utilization. In this work, we study the dynamics of mineral precipitation triggered by the mixing of two incompatible fluids in the pore space. For that, we perform core-flooding experiments and monitor fluid pressures along the sandstone specimen and simultaneously visualize the precipitation pattern by X-ray micro-CT scanning at a spatial resolution of 12 um. The experimental parameters (such as ionic concentrations and injection flow rates) are screened with the help of a numerical model, which is developed to further delineate reaction kinetics and reactive transport of the chemical species in the pore space. Our study provides insights into the mechanisms of chemical clogging and a reference for further research on reactive transport involving mineral precipitation. Understanding the time evolution of precipitation, its location in the pore space and quantifying the effect on permeability remain a challenge but are of utmost importance for optimal planning of the operational schemes. This study has received funding from the European Union as part of the EASYGO-ITN.