Cap-Rock Alteration in CO2-H2O Medium: Experimental Approach of Clays Behavior

Eric Kohler¹, Teddy Parra¹, Etienne Brosse¹, E. Tocque¹, and B. Dubacq^2
1 Institut Francais du pétrole, Rueil-Malmaison, France
² Universite J. Fourier, Grenoble, France

The CO₂ storage in depleted hydrocarbon reservoirs requires understanding the CO₂ impact on clay-rich sealing cap-rocks and demonstrating the safety of the site over thousands of years. The knowledge of the critical parameters that modify physical properties such as permeability and fracturing are key factors, which enhance the CO₂ storage capability.

The purpose of this work is to study physico-chemical reactivity of clayey materials, depending on the H₂O-CO₂ proportions of the medium. In particular, two kinds of experiments were conducted in order to determine reaction paths and diffusion processes around 150°C and 150 bar. Clay-rich samples were selected in two cap-rocks of the Paris basin. The first experiments involve grounded materials with various proportions of CO₂-H₂O mixtures. These experiments aim at increasing the reactivity and at promoting maximal mineralogical changes. Consumed or produced CO₂ and/or H₂O are quantified after each of the experimental runs. The second set of experiments involves the cm-scale fragment samples. Reaction fronts are observed that better constrain porosity vs. mineralogical changes. All samples were analyzed before and after alterations using XRD, FTIR and/or TGA to quantify mineralogical evolutions and using SEM microprobe and eventually TEM to estimate chemical variation and eventual porosity changes in the migration fronts in clay minerals.

Results show an impact of the H₂O-CO₂ medium on clayey materials in these P,T conditions and the potential consequences on cap-rock integrity are introduced.