Experiments and modeling of fracture evolution during percolation of CO₂-acidified brine through fractured limestone samples

Shunbei Oil and Gas Field has a special type of fault-controlled carbonate reservoir at depths of more than 7,000 m in Tarim Basin, China. The scale and distribution of faults determine the reservoir space distribution. The interaction among faults, geological fluid and carbonate rock and the overall impact towards the reservoir formation are hot issues of interest to scholars at home and abroad. In this study, we focused on the fractured carbonate reservoir of Yijianfang Formation in Shunbei area, and carried out dissolution experiments and 3D numerical calculations to mimic the interaction between CO₂ brine fluid and fractured carbonate reservoir along the fracture. This study combines microscopy, scanning electron microscopy and XCMT scanning, aquous cation concentration analysis, numerical simulations together to compare the changes such as fracture surface area, fracture volume, and cations concentration after the reaction. In order to understand the effects of fluid transformation qualitatively and quantitatively. The research shows the main fracture is the dominant place of physical mass transfer and chemical reaction, and the overall reaction is mainly calcium carbonate dissolution. The sample physical heterogeneity and the hydraulic property jointly control the fracture and cation spatiotemporal evolution and affect the overall reservoir physical property finally. In this study, a three-factor coupled fracture-fluid-rock geological model for the fractured carbonate reservoirs is proposed, and the potential locations for the reservoir space are presented.