How CO₂ moves underground: Visualizing flow simulations

CO₂ is stored deep underground, one key question matters more than anything else: will it stay there? To answer this, researchers run advanced computer simulations that show how CO₂ moves through geological formations over time.  

We have developed tools that make these simulation results much easier to explore and understand. They help answer important questions such as:  

• Where does the CO₂ move?
• Is there any risk of leakage?
• How much CO₂ can be safely stored?

From raw simulation data to clear insight

Even a single flow simulation produces huge amounts of data. In real projects, researchers typically run many simulations – maybe hundred or more – using slightly different assumptions to test uncertainty and sensitivity.

This creates an ensemble of possible outcomes.  

Our tools make it possible to:  

• Explore one simulation in detail
• Summarize many simulations by calculating statistics over the entire ensemble
• Easily highlight and analyze simulations that require closer inspection

Instead of working directly with complex 3D data and long tables, users get clear maps, plots, and statistics that show how the CO₂ plume develops over time.  

The tools process results from reservoir flow simulators, primarily Eclipse and Cirrus, and are designed to work seamlessly with Equinor’s Fast Model Update (FMU) framework.

They consist of two parts:  

1. General post-processing scripts based on flow simulation results.
2. Dedicated visualization plugin called CO₂ Migration, implemented in the web-based, open-source visualization framework Webviz.

CO₂ storage scenarios

The tools support these two common scenarios for storing CO₂ underground:  

1. Saline aquifers, where the underground formations are filled with brine (salty water)
2. Depleted fields, with remaining hydrocarbon gas and/or oil present. These typically have existing extensive data from oil/gas operations, and with proven containment properties.

Core features

The post-processing scripts are designed to:

• Aggregate 3D grid data into maps for relevant grid properties, such as CO₂ gas saturation, fraction dissolved in brine and CO₂ mass.
• Calculate migration time maps, showing the time it takes CO₂ to migrate to the different parts of the grid.
• Calculate mass or volume of CO₂ at each time step, classifying results based on the following categories:
  • Containment areas: For which realizations can we observe leakage into the “No-go” area?
  • User-defined regions in the 3D grid model – similar to containment areas but more general. Do any of the realizations have CO₂ migrating into region X?
  • Grid properties (gas saturation, dissolved fraction, etc) and CO₂ mass phases (free/mobile gas, residual trapping, dissolved in water).
  • Geological zones.
  • Track separate plumes from multiple injection wells.

These results can be visualized in the CO₂ Migration plugin:

• Plot aggregation and migration time maps. Either for single realization, or produce plots of ensemble statistics over multiple/all realizations.
• Various other plots, splitting or filtering results based on the categories described above:
  • Time series plot of CO₂ mass or volume. For instance, how the total mass is split into the different phases (dissolved in water, free gas, residual trapping) as a function of time.
  • Summary of CO₂ distribution for a single time step. For instance, sort realizations on by how much CO₂ is in the No-go area at the end of the simulations.
  • Box plot.
  • Cumulative probability plot.

To learn more about our work in this project, please contact: