Faults can either serve as permeable pathways or seals for fluids at a variety of scales. Hydraulic conductivity and leakage rates from faults are one of the unresolved key issues within fault seal analysis, especially for CO2 Capture and Storage (CCS) where reservoir integrity is critical, but also in geothermal operations and radioactive waste disposal. Investigation of factors that may alter the hydraulic conductivity in faults are therefore of great importance when evaluating fluid flow. Fault cores are often characterized as fault breccia or fault gouge, based on fault core fragment content. Fault gouge consist of fine-grained materials such as very-fine sand, silt and clay. The presence of phyllosilicates in fault gouge may hinder fluid flow and can therefore have a large negative effect on hydraulic conductivity. The Shale Gouge Ratio algorithm provide a widely used and well-established methodology to estimate the proportion of shaly material in a mixed clastic sequence fault zone (Freeman et al. 1998). Although this algorithm can provide a general impression on fault properties (e.g. sealing or leaking), it has certain limitations when estimating hydraulic conductivity in fault cores. By performing laboratory experiments on pre-fractured sandstones, with a varying ratio of clay and sand, we aim to better understand the effect of gouge ratio on hydraulic conductivity in faulted/fractured rocks. Several laboratory experiments were conducted to investigate the relationship between fault gouge ratio and hydraulic conductivity on pre-fractured Berea sandstone samples, which were tested under water (saline and freshwater) and oil saturated conditions. A new setup was designed to conduct shear movement in a triaxial cell, allowing for simulations of in-situ reservoir fault stress and pore pressure. Different gouge ratios (e.g. varying amount of clay and fine sand) were mixed in the laboratory and applied to machined fracture planes on cylindrical samples. Testing consisted of applying isotropic confinement stress and subsequent shear displacement. Hydraulic conductivity was estimated based on pore pressure and pore fluid flow measurements, at different stress stages during tests. Data obtained from a detailed experimental study show that fault gouge ratio play an important role on the hydraulic conductivity of fracture planes. The dataset indicates that fault gouge mineralogy, grain size and sorting, as well as pore fluid are important factors that control fluid flow in fractured sandstone units.
