Study on mechanism and microstructural characteristics of mineral dissolution and pore evolution driven by high-temperature steam flow

High-temperature steam flow in unconsolidated sandstone triggers complex coupling among hydrodynamic motion, interfacial mass transfer, and mineral dissolution, which further reshapes pore networks and alters fluid transport properties. However, the reactive–seepage coupling mechanism governing mineral dissolution-induced pore network evolution under high-temperature steam flow remains poorly understood. This work conducts sand-packed flow simulation experiments under formation compaction conditions with varied particle geometric features and steam parameters. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were used to characterize microscale grain and pore variations. The results show that grain evolution is jointly controlled by hydrodynamic shear and thermal stress. The overall dissolution rate depends on both particle and flow conditions, while the maximum dimensionless dissolution amount is governed solely by particle geometry, reaching a peak of 4.10% at a grain size of 0.10 mm. A predictive model combining boundary-layer mass transfer theory and Noyes–Whitney kinetics is established, with a high fitting accuracy of R2≥0.97. This work reveals the fundamental coupling rules of flow, mass transfer, and solid reaction in granular porous media and provides theoretical support for evaluating pore evolution during high-temperature fluid displacement.