3D Pore-Scale Modeling of Mineral Dissolution and Precipitation in Fractured Rocks

Abstract

ABSTRACT We present a pore-scale numerical modeling study of coupled fluid flow, solute transport, and mineral dissolution/precipitation in 3D fractured carbonate rocks. The injected fluid can dissolve the carbonate and release carbonate ions into the solutions, which react with Ba2+ resulting in barium carbonates (BaCO3) precipitation. Both a simplified fracture and a complex fracture geometry extracted from real shale images are considered. Simulations with a wide range of Pe and Da numbers are carried out to systematically study their effects on dissolution/precipitation patterns and on evolution of fracture geometry, porosity, and permeability. The results show that the coupled physicochemical process is strongly dependent on the Pe and Da. While similar trend of the permeability-porosity variations is obtained for the two fractures at the same Pe and Da numbers, the evolution of fracture morphology is different due to the difference in initial structure heterogeneity and wall roughness. This work reveals the interplay of advection, diffusion, and reaction in determining the fracture evolution and improves our understanding of fluid-mineral interactions in fractures. INTRODUCTION Fractures play an important role in providing preferred flow pathways in low-permeability formations and significantly enhance their permeability. They can improve gas production for shale reservoirs but can also increase the risks for leaking of CO2 from geological storage sites. The fluid-mineral reactions, including dissolution or precipitation, can cause the alteration of porous medium matrix or fracture wall. Particularly, mineral dissolution (precipitation) can increase (decrease) the pore/aperture size and hence the permeability of porous or fractured media. While there have been a lot of studies on mineral dissolution in porous or fractured media considering resultant pore-structure change (Chen, Kang, Viswanathan, et al., 2014; Kang et al., 2014; Kang et al., 2002; Liu & Mostaghimi, 2017; Rasoulzadeh et al., 2020; Starchenko et al., 2016; Verberg & Ladd, 2002; Verhaeghe et al., 2005, 2006), studies on mineral precipitation are much less (Deng et al., 2021; Kang et al., 2005; Kang et al., 2003; Menefee et al., 2020), and studies on coupled dissolution and precipitation are scarce (Chen, Kang, Carey, et al., 2014; Kang et al., 2010). Particularly, there is no high-resolution pore-scale modeling study on coupled dissolution and precipitation in three-dimensional (3D) fractures with evolving fracture geometry to our best knowledge. Consequently, the complex coupled processes including fluid flow, solute transport, dissolution/precipitation, and evolution of pore structure are not well understood.