This paper summarises the results of a benchmark study that compares a number of mathematical and numerical models applied to specific problems in the context of carbon dioxide (CO 2 ) storage in geologic formations. The processes modelled comprise ad-H. Class (B) · A. Ebigbo · R. Helmig · M. Darcis · B. Flemisch vective multi-phase flow, compositional effects due to dissolution of CO 2 into the ambient brine and nonisothermal effects due to temperature gradients and the Joule-Thompson effect. The problems deal with leakage through a leaky well, methane recovery enhanced P. Audigane BRGM, French Geological Survey, 410 Comput Geosci (2009) 13:409-434 by CO 2 injection and a reservoir-scale injection scenario into a heterogeneous formation. We give a description of the benchmark problems then briefly introduce the participating codes and finally present and discuss the results of the benchmark study.

Carbon dioxide (CO 2 ) has found wide application in the water-alternating-foam (WAF) processes for enhanced oil recovery (EOR), but few research works have been reported concerning the effect of water solubility on the CO 2 foam rheology in a porous medium. In this paper, an X-ray computed tomography (CT) study is carried out to investigate CO 2 foam flow in a consolidated Bentheimer sandstone core saturated with surfactant solution under different system pressures. As a contrast gas with much lower solubility, nitrogen foam flow is also investigated to show the essence of gas solubility effects. Careful considerations were made on the selection of contrast gases, surfactant, and experimental procedures to focus on the effect of water solubility of the gas on foam rheology in porous media. It is observed from the experiments that CO 2 foam has lower pressure loss and clearly suppressed entrance effect. With the increment of system pressure, the liquid saturation increases and the pressure loss decreases significantly for CO 2 foam flow in the sample core, while little change can be observed for N 2 foam flow. It can be concluded that water solubility is one of the important influential factors for CO 2 foam rheology in porous media.

We study opportunities for CO 2 sequestration in geological formations of the state North Rhine Westphalia in Germany. Simulations are performed for evaluating a potential site within the Bunter sandstone formation near the town of Minden in a depth of around 3,000 m using the numerical simulator TOUGHREACT. Our focus is on three CO 2 storage mechanisms: (1) hydrodynamic trapping, (2) dissolution trapping, and (3) mineral trapping. The results show that due to buoyancy the injected CO 2 phase initially migrates towards the top of the reservoir and is hydrodynamically trapped beneath the confining layer of the cap rock. Then, the CO 2 spreads laterally and dissolves partially in the formation water. The dissolution of CO 2 results in an increase of the density of the brine causing a downward migration until it settles after 10,000 years at the bottom of the reservoir. The simulations indicate that after 10,000 years, 15% (17 Mt) from a total of 114 Mt injected CO 2 are trapped hydrodynamically, 20% (23 Mt) are trapped by disso- A. lution, and 65% (74 Mt) are fixed in newly formed carbonates such as dawsonite, ankerite, and siderite. Within our study pressure increases near the injection well by a factor of 1.1 which is lower than the upper limit usually accepted in gas storage operations. The mineral reactions cause a net decrease of porosity and in turn a decrease of permeability down to 9% of the initial value in parts of the reservoir.

No abstract