Título: Effect of CO2-rich water injection on hydromechanical properties of a grain-supported limestone sample: laboratory experiment and numerical
modeling

Abstract:
To better understand the geochemical alterations of carbonate rocks during underground CO2 storage, we performed a percolation experiment
using a limestone core specimen of 2.5 cm in diameter and 4.4 cm in length. We flooded the specimen with CO2-saturated water PCO2=100 bar
and T=60 °C under a constant flow rate of 0.15 mL/min for 28 days. Fluid chemistry analyses combined with x-ray imaging, porosity measurements,
and permeability tests were used to assess the temporal ‎evolution of pore structure and permeability of the altering specimen. ‎The
monitoring procedures reveal rapid and progressive dissolution of calcite, yielding enhancements of 9.6% and 3 orders of magnitude in the
rock porosity and permeability, respectively. X-ray images also illustrate that the porosity ‎enhancement coincides with the creation of
a large wormhole inside the specimen, presumably ‎developed in response to the natural heterogeneity of the rock. To gain an improved insight
into the effect of rock heterogeneity on the dynamics of ‎wormhole formation and the evolution of fluid flow inside the specimen, we mapped
X-ray images onto a continuum domain and developed a 3D reactive transport model of the experiment. The porosity-permeability
relationship and ‎mineral surface area are found to impose first-order impacts on model predictions of calcite dissolution inside the limestone
sample. Thus, we calibrated these parameters against the measured variations in the aqueous chemistry of the outflows. The calibrated
model, featuring a powerlaw-based porosity-permeability relationship with an exponent as high as 10, nicely captures the imaged wormhole
structure. Our findings have significant implications for the process understanding of wormhole formation and its effect on field-scale CO2 storage.