Size-dependent transport and adhesion of heat-activated resin droplets in geothermal fractures

The presence of rapid flow pathways through large, well-connected fractures reduces heat-exchange efficiency and the economic viability of enhanced geothermal systems (EGSs). However, when high permeability fractures form during fracking or seismic activity, only a few methods are available to mitigate their impact on the performance of EGSs. We recently proposed a method that employs thermally activated epoxy resin droplets that are transported with the flow to hot regions where the resin droplets foam and adhere to the fracture walls, thus selectively reducing the local permeability. A proof of concept was reported; however, the transport dynamics and statistical behavior of droplet adhesion were not fully characterized. Here, we report a hydrodynamic model for the transport and adhesion behavior of thermally activated resin droplets and laboratory experiments in simple fractures. We characterize the velocity of resin droplets in fractures considering the distribution of injected droplet size and the onset of thermal activation on volume expansion, adhesion, and curing. The resulting blockage of the fracture during laboratory experiments was in good agreement with the adhesion predicted without feedback. Initially, isolated large droplets with low velocity adhere near the transition to the hot region and alter the flow field, resulting in interactions with subsequent droplets. The overall pressure drop across the fracture gradually increases even after resin injection stops, demonstrating the contribution of foaming and curing after attachment to hydraulic blockage. The hydrodynamic model supported by observations provides a mechanistic basis for the prediction of resin droplet blockage and subsequent flow rerouting in large geothermal fractures.