The race is on to develop the most secure solution for storing CO2 in the Earth’s crust. A Norwegian company, Numerical Rocks AS, has developed a method for studying precisely how this greenhouse gas is bound inside rock.

CO2 capture and storage is a key measure for mitigating climate change. The gas can be pumped into the earth’s crust and deposited in various types of porous rock that is currently saturated with seawater. But how secure against leakage is this practice, and what is the holding capacity of different kinds of rock? Numerical Rocks AS has been studying how carbon dioxide moves and becomes “locked inside” the microstructure of sandstone and other rock.

Using computer simulations of two-phase flow (CO2 and water) incorporated directly into 3D images of reservoir rock, researchers and petroleum operators can calculate how gases and fluids either move or get trapped by capillary forces in the tiny hollow spaces (called capillaries) within a porous rock. The method itself is simple enough, but the data algorithms behind it are extremely complex and require high-performance computational power.

Reservoir parameters are calculated based on a slow, continuous flow of water and CO2 within the pore system of the rock. It is represented on a digital 3D image of the rock. The result is an animated 3D simulation of fluids within the rock, which enhances researchers’ physical understanding of how these substances behave.

Stationary flow refers to the snail-paced movement of substances, typically just 30 cm per day, that takes place far from the injection well. This flow is controlled by capillary pressure conditions. The CO2 trapped in a rock’s pores by capillary force does not leak out, even if the impermeable rock types above it crack open. Numerical Rocks is now studying flow under non-stationary conditions – in the immediate vicinity of the injection wells – where the pressure is variable and flow occurs much more quickly.