Geochemistry of silicate-rich rocks can curtail spreading of carbon dioxide in subsurface aquifers

TL;DR

This study shows that chemical reactions in silicate-rich rocks can significantly hinder CO2 convection in subsurface aquifers, potentially trapping CO2 near the surface for centuries and affecting sequestration strategies.

Contribution

It provides a new theoretical and experimental understanding of how silicate-rich rocks impact CO2 transport, challenging previous assumptions about efficient deep sequestration.

Findings

Chemical reactions in silicate rocks inhibit CO2 convection.

In carbonate rocks, CO2 streaming persists.

Silicate-rich rocks can trap CO2 near the surface for centuries.

Abstract

Pools of carbon dioxide are found in natural geological accumulations and in engineered storage in saline aquifers. It has been thought that once this CO2 dissolves in the formation water, making it denser, convection streams will transport it efficiently to depth, but this may not be so. Here, we assess theoretically and experimentally the impact of natural chemical reactions between the dissolved CO2 and the rock formation on the convection streams in the subsurface. We show that, while in carbonate rocks the streaming of dissolved carbon dioxide persists, the chemical interactions in silicate-rich rocks may curb this transport drastically and even inhibit it altogether. These results challenge our view of carbon sequestration and dissolution rates in the subsurface, suggesting that pooled carbon dioxide may remain in the shallower regions of the formation for hundreds to thousands of years. The deeper regions of the reservoir can remain virtually carbon free.