Study of multi-size proppant breakage mechanism under deep reservoir conditions for enhanced geothermal system development

Proppant breakage is a significant concern in fracturing treatments in deep reservoirs, reducing the efficiency of enhanced geothermal systems (EGS). However, little research has been conducted on the breakage process of proppants under high closure stress conditions. A visualization experiment was designed to investigate processes of proppant breakage and layer deformation in real-time under 100 °C and high closure stress (0-50 MPa) conditions. We observed significant non-uniform breakage in the multi-size proppant layer, which resulted in large-size pores with high connectivity in the regions of low breakage degree, potentially maintaining permeability. Moreover, the non-uniform breakage forms a composite structure in two stages. This process mitigates subsequent proppant breakage, thereby preserving the non-uniform breakage pattern and maintaining a locally high-connectivity porous structure. In addition, we discussed the nonlinear deformation and stiffness of the proppant layer under stress loading. Finally, the applicability of the conclusions has been demonstrated by comparing granite-proppant experiments with the same conditions. The non-uniform breakage characterization of multi-size proppant layer in the granite-proppant experiments was observed as well. This research reveals the breakage mechanism of the multi-size proppant, which is expected to facilitate the optimization of proppant placements in deep fracturing operations.