Multiphase CO2-brine transport properties of synthetic fault gouge

摘要

Faults are key components in defining fluid migration pathways and seals in sedimentary basins. The sealing capacity of faults is closely related to the petrophysical and geomechanical properties of fault gouge. Clay smear, cataclasis, and diagenesis favor a high capillary breakthrough pressure and low permeability in clastic sediments, and therefore fault gouge seal. However, significant uncertainty remains in accurately predicting the sealing capacity of faults for CO2 storage. We conducted a series of experiments, including absolute permeability, breakthrough pressure, and post-breakthrough CO2 permeability measurements on synthetic fault gouge samples, made from homogeneous mixtures of Frio sand and Anahuac shale, lithofacies of tertiary sediments in the Gulf of Mexico basin. The results show that the permeability of synthetic fault gouge decreases by about one order of magnitude with increments of 10 wt% of clay (mostly smectite) from the Anahuac shale. Independent of clay content and bulk porosity, all permeability measurements scale with the void ratio of the clay fraction. The breakthrough pressure of synthetic fault gouge increases by approximately half order of magnitude with increments of 10 wt% clay. The samples with clay content above 40 wt% reach a breakthrough pressure equivalent to a (supercritical) CO2 column height of more than 100 m. The measurements on fault gouge properties are meaningful to quantitatively evaluate fault sealing capability and migration of buoyant fluids through faults in sand-shale sequences.