Experimental and modeling study of the interaction between a crushed marl caprock and CO2-rich solutions under different pressure and temperature conditions

Abstract

Carbon storage is regarded as a potential technology to reduce CO2 emissions. This study is concerned with CO2 storage in a reservoir rock (limestone) which is a deep saline aquifer containing a NaCl− and sulfate-rich groundwater in equilibrium with calcite and gypsum. The reservoir rock is overlain by a very low permeability formation (marls), which acts as a caprock. During and after CO2 injection, the resulting CO2-rich acid solution gave rise to mineral dissolution and precipitation processes. These reactions led to changes in porosity, pore structure and permeability of the caprock and also to the alteration of its CO2 seal capacity.Flow-through experiments using columns filled with three crushed samples (marly limestone, bituminous black shale and marl), which constitute the Hontomín caprock unit, were conducted under different PTotal-pCO2 (atmospheric: 1–10−3.5bar, subcritical: 10–10bar and supercritical: 150–37bar) conditions and T (25 and 60°C) using gypsum-undersaturated and gypsum-equilibrated solutions to evaluate the Hontomín caprock reactivity. 1D reactive transport modeling of the results enabled us (1) to better understand the overall processes that bring about the large dissolution of calcite, minor dissolution of aluminosilicates and the precipitation of gypsum, kaolinite, zeolites and some aluminum and iron oxides and oxyhydroxides and sulfates and (2) to evaluate their implication for the hydrodynamic properties of the caprock. An increase in porosity over the column length, which mostly occurred near the inlet, was calculated.