Carbon Dioxide (CO2) injection in geological formations is a potential solution to control anthropogenic greenhouse gas emissions. Value added processes such as CO2 flooding for enhanced oil/gas recovery and disposal processes such as CO2 injection in saline aquifers are among the most promising sequestration processes. Transport, storage, and sequestration of CO2 in these processes involve dispersion and reaction phenomena in porous media. The overall performance of any CO2 injection project depends on the mechanistic aspects of CO2 interaction with the natural porous system at pore scale, core scale, and the heterogeneity of the geological formations. The physics of transport and sequestration of CO2 for different CO2 injection processes in a pore-level scale is first described. These pore-level events are then related to core-scale (gridscale) coefficients using an advanced upscale theory. At the pore-level, a unit cell consists of different sand grains and the interstitial space around them. CO2 enters the unit cell by convection and diffusion and interacts with the interstitial fluid and sand grains. Such local events are transformed into a macro-scale level by adopting periodic boundary conditions for contiguous unit-cells and applying Taylor-Aris dispersion theory. Using this theory, macroscopic coefficient for the transport of CO2 molecules in porous media are determined. These macroscopic coefficients may be used in dispersionreaction constitutive equation to calculate CO2 concentration in time and space.
The three main options for the geological storage of CO2 are saline aquifers, and existing oil and gas fields. These can be divided into two economic end-members. First are purely storage options, whereby the CO2 is injected without any direct financial benefits, e.g. saline aquifers, although carbon tax credits may improve the financial viability of this option. The second are utilization options where the CO2 injection process has additional economic benefits through enhanced hydrocarbon recovery(1).
Many of the oil and gas pools in North America have reached the maturity of economic production. CO2 injection is an option to rejuvenate oil or gas production from these reservoirs(2). Miscibility of CO2 and oil improves microscopic displacement efficiency in these pools(3,4). Saline aquifers are defined as aquifers without potable water. Saline aquifers have the potential to store a huge volume of the total CO2 emissions in various locations near the sources of the CO2 emission, e.g. power plants(5–7).
For any CO2 storage or utilization process to be successful, it must be technically and economically feasible, effective in significantly reducing CO2 emission for a long period of time, and be safe for people and environment. Reliable mathematical models are needed to predict the success of a CO2 sequestration process in geological formations. The efficiency of a CO2 sequestration process is defined as: Equation (1) (Available in full paper)
Suppose that CO2-free fluid flows through the porous bed. At time t=0 let a swarm of CO2 molecules be instantaneously introduced into the bed. Each CO2 molecule will be transported through the interstices by convection and diffusion, with some being interacting (ab/adsorption, reaction) with the interstitial fluid and sand grains.
