Carbon mineralisation in basalts is a promising cost-effective way to permanently store CO2 in view of climate change mitigation. In this work, the impact of carbon mineralisation on the hydromechanical properties of a basaltic sample is studied. Unlike previous studies where CO2 dissolved in fresh water is considered, here CO2 dissolved in saline water is used aiming at a more ecological application of the technology at large scales. First, the flow properties of the material are measured in the lab before and after a 2-month exposure to dissolved CO2 under field-representative conditions. Carbon mineralisation can substantially alter the pore space of the material, resulting in reduction of porosity, flow properties, and consequently overestimation of the injection and storage efficiency. The experimental results show a permeability reduction of half an order of magnitude, suggesting porosity reduction due to mineral precipitation. Image analysis of x-ray tomographies of the tested sample (resolution 50 μm/px) before and after CO2 exposure show a total porosity reduction of 2.4 %. To better understand the evolution of the pore network before and after mineralisation, pore network simulations are performed on the real 3D porosity of the material acquired from the x-ray images. Two types of porosity are considered, macro (pores > 50 μm) and micro (solid matrix porosity). Reduction of the size of macro-pores does not impact flow. To reproduce the post-exposure flow results, decrease of the solid matrix porosity is required, revealing that carbon mineralisation is more prone to take place in the micro-pores.