Role of Convective Mixing in the Long-Term Storage of Carbon Dioxide in Deep Saline Formations

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractStorage of carbon dioxide in deep formations is being actively considered for the reduction of greenhouse gas emissions. Relevant experience in the petroleum industry comes from natural gas storage and enhanced recovery using carbon dioxide, but this experience is over a time scale less than the hundreds or thousands of years required for carbon dioxide storage. On these long time scales different mechanisms need to be considered.In the long-term the dominant mechanism for dissolution of carbon dioxide in formation water is convective mixing rather than pure diffusion. This arises because the density of formation water increases upon dissolution of carbon dioxide, creating a density instability. Linear stability analysis has been used to estimate the time required for this instability to occur in anisotropic systems. For sufficiently thick formations with moderate vertical permeability, this time is years to decades. Further approximate analysis shows that the time needed for the injected gas to dissolve completely is typically much longer, of the order of hundreds to thousands of years, depending on the vertical permeability. This theoretical analysis is found to be in broad agreement with the results of fine scale reservoir simulations. Laboratory experiments on an analogous system demonstrate the same phenomena.

Lifetime of carbon capture and storage as a climate-change mitigation technology

“…Trapping occurs primarily after injection, when the CO 2 migrates due to the aquifer slope and the natural head gradient. As the buoyant plume of mobile CO 2 (dark gray) rises and spreads away from the well array, residual trapping immobilizes blobs of CO 2 in its wake (light gray) (19,29,30), and solubility trapping shrinks the plume from below (blue) (20,21). and opposite slope until returning to the current rate (Fig.…”

“…Although trapping can be analyzed over a wide range of length scales, we consider trapping at the large scale of an entire geologic basin because large volumes of CO 2 will need to be stored to offset emissions (3). We consider residual trapping, in which blobs of CO 2 become immobilized by capillary forces (19), and solubility trapping, in which CO 2 dissolves into the groundwater (20,21), because these mechanisms operate over relatively short timescales and provide secure forms of storage ( Fig. 1 A and B).…”

Dissolution Trapping of Carbon Dioxide in Reservoir Formation Brine – A Carbon Storage Mechanism

“…The CO 2 -enriched brine has a slightly higher density than the original brine (Ennis-King and Paterson 2005, Moortgat et al 2011). This leads to gravitational flow instabilities in the reservoir (Riaz et al 2006, Pau et al 2010, and it is believed that the CO 2 -rich brine sinks in the reservoir over hundreds to millions of years (Bachu 2000, Ennis-King and Paterson 2005, Lindeberg and Wessel-Berg 1997 in the form of thick and thin fingers (cp. Figures 1 and 2), however this is an active area of research and it has been suggested that this mechanism is considerably faster (Moortgat et al 2011).…”

Investigation of CO2 Plume Behavior for a Large-Scale Pilot Test of Geologic Carbon Storage in a Saline Formation

“…In fact, CO 2 -saturated brine is denser than native brine. As CO 2 -laden brine sinks deeper into the formation, it can set up circulation patterns that enable more free-phase CO 2 to come into contact with native brine, enabling more dissolution to occur (Ennis-King and Paterson 2005;Pruess and Zhang 2008). (4) Mineral trapping: CO 2 reacts with rock minerals to form carbonate compounds, typically over very long time scales Xu et al 2003Xu et al , 2005Gherardi et al 2007).…”