Effects of a Regional Aquifer on the Evolution of a Dense CO2-Charged Brine

Abstract:

Carbon Capture and Storage (CCS) within geological reservoirs is recognised as an important solution to combat the observed changes in the Earth’s climate attributed to the release of carbon dioxide (CO₂) and other greenhouse gases into the atmosphere. Such storage must be long-term and secure thus the ability to model the fate of CO₂ and CO₂-charged brines as they migrate within through geological carbon storage reservoirs is critical to obtaining regulatory approval. However, the complexities of flow in natural heterogeneous reservoirs make it essential to test model results against observations of real systems; this can be difficult due to their inaccessibility and the expense of gathering adequate data. At Green River, CO₂ and CO₂-charged brines leak into overlying aquifers during migration to the surface through the Little Grand Fault. As the CO₂-charged brine leaks it forms a series of gravity currents and mixes with the formation fluids. Downhole fluid samples from the upper aquifer of the Navajo Sandstone suggest that regional aquifer flow and sedimentological heterogeneities have a large impact on the evolution and mixing of the CO₂-charged plume¹. Theoretical studies show that by imposing a regional background flow we alter the dynamics and evolution of a dense plume. To test the theory, a series of laboratory experiments were conducted; a constant flux of a denser brine solution was released from a point source at the base of a porous medium filled with flowing fresh water. We present here the theory and laboratory experiments and compare these findings to the vertical variation of conservative tracers, i.e. Na and Cl, within the formation fluids of the Navajo Sandstone.

1) Kampman, N., Maskell, A. and others, 2014. Drilling and sampling a natural CO₂ reservoir: Implications for fluid flow and CO₂-fluid-rock reactions during CO₂ migration through the overburden. Chemical Geology 369, 51–82.