Scalable Simulation of Subsurface CO2 Sequestration Processes: the GEOS Open-Source Platform

Summary:

• Motivation: CO2 sequestration in subsurface formations is a key technology for mitigating climate change.

• MALSTROM project:https://www.llnl.gov/article/46901/llnl-partners-open-access-co2-storage-simulator

• GEOS: https://github.com/GEOS-DEV/GEOS

• DOE Report: Accelerating Breakthrough Innovation in Carbon Capture, Utilization, and Storage

• There are many projects that capture CO2 from point sources or directly from the atmosphere and need subsurface storage

• Simulation of CO2 sequestration

• Model the process of injecting CO2 deep underground and the long post-injection evolution of the CO2 plume(s)

• Supercritical state: High density, low viscosity

• Consideration:

• Safety

• Injectivity

• Capacity

• Containment

• Interactions

• Long-term fate

• Phenomena to model

• Multiphase flow dynamics

• Hydro-fracturing

• Hydro-shearing

• Fault reactivation

• Induced seismicity

• Well integrity

• Surface deformation

• Challenges

• Multi-physics

• Multi-scale

• HPC

• Sequestration process

• Capture CO2 from either point or distributed sources.  Point sources include cement plants, steel manufacturing, fertilizer production, biomass energy, natural gas power plants, blue hydrogen production, etc.  There is recent interest as well in “direct air capture,” pulling CO2 directly from the atmosphere.  This is energy inefficient compared to point source capture but may be necessary long-term to achieve climate change targets. 

• Compress the CO2, and inject under ground (800 meters +) into small pores within rock formations

• Salt-water aquifer

• Supercritical CO2 initially exists as a separate phase, but begins dissolving into surrounding in-situ brine.

• Trapping process:

• Structural: Solid, impermeable rock layers above injection formations to keep the CO2 contained.

• Residual: CO2 trapped in micron-scale pores within the rock

• Dissolution trapping: CO2 dissolves into surrounding salt water and no longer buoyant

• Mineral trapping: CO2 reacts with surrounding rock, creating new solid minerals (e.g. Ankerite: https://www.mindat.org/min-239.html)

• Mineral trapping is the biggest hope but it takes a long time, so main focus of project design is to rely on structural, residual and dissolution trapping

• CO2 sequestration dynamics are challenging to model because several important effects are at play: gravity currents, convective dissolution, geomechanical interactions

• Model: 

• Darcy’s Law-based model tuned to the specific dynamics of CO2 (https://www.ldeo.columbia.edu/~martins/climate_water/lectures/darcy.html)

• Fluid dynamics of CO2-saturated water falling into CO2-free in-situ water as “finger” shapes, with low-Reynolds number

• Length scales:

• Rock pores are micron-size

• CO2 fingers start at the cm scale

• Rock formations are kms in size

• Time scales: years - Kyears

• 10's to 100's years for dissolution dynamics to fully engage

• 100s of years for dissolution process to complete

• Data-limited: 

• Cores and wellbore logging tools at wellbore locations

• Well-based observations of flow rates, pressure, temperature, fluid composition

• Remote geophysical imaging methods.  Mainly active 3D/4D seismic imaging and passive microseismic monitoring and tomography.  Other techniques such as satellite-based InSAR, electromagnetics, gravity surveys, and various types of fiber optic monitoring may be applicable depending on site characteristics.

• Data assimilation and uncertainty quantification are critical for aligning model to reality

• Multiscale poromechanics

• Flow of CO2 fluid through solid rock matrix

• Structural mechanics of the rock matrix to evaluate its stability and impact of CO2 injection on the rock matrix

• Fluid-structural interactions:

• Multiple fluids: supercritical CO2, salt-water, possibly hydrocarbons (multiple fluid phases)

• Multi-phase flow

• Interphase mass transfer

• Flow-GeoMechanics Simulation: Physics, multi-scale, coupled flow+mechanics, IHU discretization, non-linear solvers, scalable algorithms

• Simulator objectives:

  • Unstructured geo grids: faults, fractures

  • Tightly coupled flow, transport, mechanics

  • Solvers: algebraic and multi-level (different solvers for each scale/physics)

  • Scalable HPC

• Validation

  • Related communities to be inspired from:

    • Oil and gas simulation

    • Subsurface hydrology

  • Careful use of available data

    • Understanding of structural and regional geology

    • Seismic information

  • Need to constantly adapt the model based on changes in data: couple forward and inverse problems

  • Confidence and processes improve as you keep doing projects

• Model uncertainty

  • Physics at pore-scale is well-known and we are confident about our approximations of this process

  • Most of the uncertainty is in the details of the geology of the target formation and the layers around it

    • Seismic surveys give you resolution at many meters

    • Need to create fine-grained of geology with appropriate discontinuities and roughness that is consistent with the seismic survey data

    • Use-case for generative models (e.g. ML) that create rough geology models

• HPC scalability

  • GEOS can be used at high resolution on leading-scale supercomputers

  • Or at lower scale on smaller clusters

  • Goal: suites of multi-fidelity resolutions, coupled with neural surrogates