Orthogonal experimental investigation on permeability evolution of unconsolidated sandstones during geothermal fluid reinjection: A case study in the Minghuazhen Formation, Tianjin, China

Geothermal fluid reinjection (GFR) is vital for sustainable sandstone hydrothermal geothermal resource extraction. However, the permeability damage mechanisms of sandstone geothermal reservoirs due to reinjection remain unclear. This study aimed to investigate the permeability evolution of unconsolidated sandstone during GFR through an orthogonal experiment. The influence mechanism of the factors, including temperature, injection rate, confining pressure, geothermal fluid concentration (GFC), and depth, on sandstone permeability is also discussed. The results showed the sandstone samples suffered permeability damage in 34.62–72.73 %. Particle clogging emerged as the primary mechanism responsible for the permeability damage, serving as a crucial bridge in understanding the influences of the factors on sandstone permeability. Efficient GFR requires the optimization of reinjection conditions tailored to the characteristics of geothermal reservoirs. Sensitivity analysis showed that the order-sensitive characteristic of permeability damage to the factors was injection rate > GFC > temperature > depth > confining pressure. Through the optimization of reinjection parameters, the heat exploitation performance under the worst permeability damage case can be improved by 1.77–1.93 times. This study could offer valuable insights into the challenges and considerations associated with GFR in sandstone reservoirs.