Fluid flow across the fracture-matrix interface in chalk

Fractures are abundant features in the subsurface, thus occurring in groundwater, hydrocarbons, and geothermal reservoirs, and may significantly enhance or reduce the permeability. The fracture-matrix interface represents a unique domain of variable mineralogy, pore space geometry and fluid flow conditions. Mineralogical changes due to coating may result in the wettability of the fractures being changed and thus impacting the two-phases flow properties of the fractures. Fractures with different coatings are CT scanned and analyzed by SEM/QEM. Based on the obtained SEM image a 2D demonstration of the numerical domain (pore space) is built, and velocity fields for flow in multiple directions calculated to assess the flow properties in the presence of coating. The calculated equivalent permeability tensors are compared for fracture-matrix interfaces with and without coating. We discuss the critical role of the interfaces not only on the permeability reduction also on the ability of fluid phases transport across the fracture-matrix interface as a function of pore geometry and mineralogy of the coatings. This study highlights the abundance and variety of coatings precipitated along the fracture-matrix interfaces. This abundance questions the reliability of previous flow studies on fractures that relies exclusively on the physical properties of the host rock.