ExpeCO2SolTrap · Experimental investigation of CO2 solubility trapping in heterogeneous 3D porous media

Experimental investigation of CO2 solubility trapping in heterogeneous 3D porous media

CONTEXT: When CO2 is injected into geological formation at depths larger than 900 m, it is in supercritical state (scCO2) due to the high pressure and temperature; hence its viscosity and density are smaller than those of the interstitial fluid. Upon injection, the scCO2 thus moves to the top of the geological formation by buoyancy. It is then lying on top of the resident brine, in which it is partly soluble, which creates a layer of brine enriched with dissolved CO2, at the boundary between the sc CO2 and the pure brine. As the mixture is denser than pure brine, a gravitational convection eventually occurs, which brings CO2 in its dissolved form to the bottom of the aquifer, while displacing CO2-devoid brine from the bottom of the formation towards the brine-sc CO2 interface, which allows for further dissolution of the scCO2 into the liquid phase . Through this convective dissolution process, CO2 can thus remain trapped inside the formation by gravity over long times, with a very low risk of leakage to more superficial geological formations or the Earth’s surface. This mechanism for subsurface sequestration of CO2, denoted solubility trapping, has attracted much attention in the last 10 years. However: (i) predictions of the time evolution of the dissolution flux still rely mostly on Darcy scale modelling, which cannot account for the coupling between the mechanism of the gravitational instability and the heterogeneous pore scale flow and solute mixing; and (ii) the effect of medium heterogeneity has never been studied experimentally. OVERALL OBJECTIVE: The primary objective of ExpeCO2SolTrap is to characterize quantitatively the convective dissolution of CO2 in heterogeneous three-dimensional porous media from pore scale measurements in the laboratory. The project has defined two specific objectives in this project, • Understanding the coupling of gravitational pore scale flow and solute mixing, and how it impacts large scale convection, in a homogeneous granular porous medium. • Characterizing the impact of Darcy scale medium heterogeneity on solubility trapping This project aims at investigating Rayleigh-Taylor instabilities between two miscible liquids in a granular porous medium. The growth rate of fingers during the convective dissolution has been examined. In this regard, we employed an light source positioned behind a homogeneous quasi-2D porous medium consisting of transparent solid grains and laser induced fluorescence to measure the concentration field. The insights from these experiments are compared to numerical simulations in COMSOL and the comparison between the experiments and simulations on the growth rate of the instabilities will provide information on how pore scale heterogeneities impact the large scale convection in a homogeneous porous medium. IMPACT OF THE PROJECT: The results of ExpeCO2SolTrap will be directly related to CO2 sequestration in deep saline aquifers but also more generally to the field of environmental fluid mechanics, and therefore they will be primarily communicated to scientists and professionals in the fields of CCS and environmental fluid mechanics.

Data: CORDIS, © European Union