Exploring the mineral dissolution-precipitation processes in fracture-fluid-rock systems based on simulation experiments

Water-rock interactions in fracture systems and their significance to reservoir formation have always been a hot topic of interest for scholars around the world. Fluid may flow and transport along the fractures, dissolve surrounding rocks, precipitate new minerals, and change the morphology of storage space, all playing critical roles in the formation and distribution of carbonate reservoirs as well as hydrocarbon migration and accumulation. It is therefore of great theoretical and practical significance to identify the genetic mechanism of deep and ultra-deep fractured carbonate reservoirs. In this study, we carried out high-temperature and high-pressure dissolution simulation experiments on samples from the Ordovician Yijianfang Formation in the Shunbei area of Tarim Basin and performed numerical simulation with tools such as TOUGHREACT to identify the interaction mechanism between brine with dissolved CO₂ and carbonate rocks, to investigate the influence of temperature, pressure, fluid property and physical heterogeneity, and to calculate the Ca²⁺ diffusion properties and mineral dissolution/precipitation trends. The results show that the overall reaction is dominated by calcite dissolution with an increase in fracture width, number and volume, as well as sample permeability and porosity, indicating improvement of reservoir quality. This study clarifies that the physical heterogeneity and fluid hydraulic properties promote the main fractures as the main flow channels. The flow and reaction processes promote each other and together determine that the main fractures will not only be the dominant channels for fluid flow and the main place where water-rock reactions occur, but will also be the dominant reservoir space for oil and gas.