Permeability alteration due to salt precipitation driven by drying in the context of CO2 injection

Abstract

Injection of large quantities of CO2 for underground geological storage in shallow or deep saline aquifers will lead to a strong water desaturation of the near wellbore because of drying mechanisms. Even the capillary trapped water can be removed by thermodynamical transfert of water vapour in the CO2 phase. In this context, drying mechanisms can precipitate the salt present in the aquifer and then lead to injectivity alteration. In this study, we investigated experimentally the alteration of permeability induced by drying of brine in porous media for different rocks and different brines. Initial characterization on four types of dry rock sample representative of storage rocks was performed including gas permeability and porosity measurements. Two sandstones and two carbonate rocks of large and medium permeability were tested to evaluate the effect of rock type and initial permeability on the injectivity alteration. Each sample was fully saturated with a brine of different salt composition (KCl, NaCl and Keuper brine, a mixture of salt representative of the Paris Basin brine aquifer) and different salinity up to 250 g/L. The samples were then completely dried in an oven at controlled temperature and with vapour evacuation. Return gas permeabilities were then measured on each sample after full drying. Local analysis at the pore scale, with scanning electron microscopy and micro-Xray scanner have been done to observe the type of flow obstruction and the spatial repartition of the salt deposit in the pore matrix.