Polymer Fluids Potential in Geothermal Systems

Polymer fluids are used in subsurface operations for either resource recovery or soil remediation. These fluids can carry remedial amendments and proppant particles, enhancing their mobility across geological formations; improve reservoir permeability and, hence, increase the production, adding viscosity-modifier chemicals. A complex microstructure of these fluids typically results in a shear-thinning (ST) behavior at the hydrodynamic scale. At the fracture scale, the interplay between the medium’s heterogeneity and the fluid’s rheology may result in strong flow localization and in a fracture transmissivity up to two orders of magnitude higher than that obtained with water. Recent modeling results relate heat transport in geological fractures and heat transport within the rock matrix to transmissivity. These findings suggest that polymer working fluids can be used in enhanced geothermal systems (EGS) to improve heat exchange and the production efficiency. Moreover, the complex rheology of such fluids can be exploited to infer field-scale structural information about the fractured formation from heat tracer tests by inverse modeling. Polymer fluids and ST CO2-based fluids might provide a novel greener, water-saving solution for working fluids in EGS. Several challenges must be faced to quantitatively characterize the impact of these fluids on flow and heat transfer in fractured media at different scales and, consequently, to assess their cost effectiveness. These are the objectives of the GEONEAT project, funded by the European Commission through the Marie Skłodowska-Curie Actions under the Horizon Europe framework program.