Carbon dioxide capture and sequestration (CCS) in deep geological formations has recently emerged as an important option for reducing greenhouse emissions. If CCS is implemented on the scale needed to make noticeable reductions in atmospheric CO2, a billion metric tons or more must be sequestered annually—a 250 fold increase over the amount sequestered today. Securing such a large volume will require a solid scientific foundation defining the coupled hydrologic-geochemical-geomechanical processes that govern the long-term fate of CO2 in the subsurface. Also needed are methods to characterize and select sequestration sites, subsurface engineering to optimize performance and cost, approaches to ensure safe operation, monitoring technology, remediation methods, regulatory overview, and an institutional approach for managing long-term liability.

CO2 Sequestration in Deep Sedimentary Formations

The Intergovernmental Panel on Climate Change assumes the warming of the climate system, associating the increase of global average temperature to the observed increase of the anthropogenic greenhouse gas (GHG) concentrations in the atmosphere. Carbon dioxide (CO 2 ) is considered the most important GHG, due to the dependence of world economies on fossil fuels, since their combustion processes are the most important sources of this gas. CO 2 concentrations are increasing in the last decades mainly due to the increase of anthropogenic emissions. The processes involving CO 2 capture and storage is gaining attention on the scientific community as an alternative for decreasing CO 2 emission, reducing its concentration in ambient air. However, several technological, economical and environmental issues as well as safety problems remain to be solved, such as the following needs: increase of CO 2 capture efficiency, reduction of process costs, and verification of environmental sustainability of CO 2 storage. This paper aims to review the recent developments (from 2006 until now) on the carbon capture and storage (CCS) methodologies. Special attention was focused on the basic findings achieved in CCS operational projects.

Recent developments on carbon capture and storage: An overview

A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a high-level list of capabilities for each of the codes, along with a selective list of applications that highlight their capabilities and historical development.

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Reactive transport codes for subsurface environmental simulation

Geological storage of CO2 in saline aquifers—A review of the experience from existing storage operations

Role and impact of CO2–rock interactions during CO2 storage in sedimentary rocks

Reactive transport modelling of the impact of CO2 injection on the clayey cap rock at Sleipner (North Sea)

This paper presents a 2D reactive transport model of long-term geological storage of carbon dioxide. A data set from the Utsira formation in Sleipner (North Sea) is utilized for geochemical simulation, while the aquifer is approximated as a 2D cylindrically symmetric system. Using the reactive transport code TOUGHREACT, a 25 year injection scenario followed by a 10,000 year storage period are simulated. Supercritical CO2 migration, dissolution of the CO2 in the brine, and geochemical reactions with the host rock are considered in the model. Two mineralogical assemblages are considered in the Utsira formation, a sand formation that is highly permeable and a shale formation representing four semi-permeable layers in the system that reduce the upward migration of the supercritical CO2. The impacts of mineral dissolution and precipitation on porosity are calculated. Furthermore, the 2D cylindrical geometry of the mesh allows simulating both the upward migration of the supercritical gas bubble as well as the downward migration of the brine containing dissolved CO2. A mass balance of the CO2 stored in, respectively, the supercritical phase, dissolved in the aqueous phase, and sequestered in solid mineral phases (carbonate precipitation) is calculated over time. Simulations with lower residual gas saturation and with different mesh refinement are also performed to test the sensitivity on mass balance estimates.

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Two-dimensional reactive transport modeling of CO2 injection in a saline aquifer at the Sleipner site, North Sea

Geochemical and solute transport modelling for CO2 storage, what to expect from it?

Chemistry of fluids from a natural analogue for a geological CO2 storage site (Montmiral, France): Lessons for CO2-water-rock interaction assessment and monitoring

Irina Gaus

Papers

Role and impact of CO2–rock interactions during CO2 storage in sedimentary rocks

Reactive transport modelling of the impact of CO2 injection on the clayey cap rock at Sleipner (North Sea)

Two-dimensional reactive transport modeling of CO2 injection in a saline aquifer at the Sleipner site, North Sea

Geochemical and solute transport modelling for CO2 storage, what to expect from it?

Chemistry of fluids from a natural analogue for a geological CO2 storage site (Montmiral, France): Lessons for CO2-water-rock interaction assessment and monitoring