Modeling CO2 storage using 6X provides an accurate estimate of the volume of CO2 that can be stored and evaluation of the risks associated with CO2 storage.
There are a number of studies examining the geological storage of CO2 in saline aquifers. Due to the complexity of these studies, reservoir simulation is the best tool for analysis. Using 6X allows 2D or 3D simulation using larger grid cells, which allows simulation of the entire saline reservoir for the multiple wells and long times (1000+ years) associated with CO2 storage.
Modeling CO2 storage using 6X provides an accurate estimate of the volume of CO2 that can be stored and evaluation of the risks associated with CO2 storage.
There are a number of studies examining the geological storage of CO2 in saline aquifers. Due to the complexity of these studies, reservoir simulation is the best tool for analysis. Using 6X allows 2D or 3D simulation using larger grid cells, which allows simulation of the entire saline reservoir for the multiple wells and long times (1000+ years) associated with CO2 storage.
1. Solubility trapping. CO2 dissolved in water
- CO2 solubility in water is a function of temperature, salinity, and mixing
- 6X internally calculates the CO2 solubility as a function of temperature and salinity using GENPV
- The mixing of CO2 with resident brine in thicker homogeneous zones occurs in a number of stages:
- Normal solubility of CO2 in water as a function of pressure
- A layer of dense brine forms along the interface of free CO2 and resident brine
- As this dense brine layer becomes unstable, it sinks creating ganglia or fingers, forcing fresh resident brine to rise, setting up counter-current mixing/flux (constant flux stage)
- Fingers merge creating sheets or plumes that sink in larger volumes
- Fingers occur at a scale that limits cell and timestep size. Using magnitude and frequency of fingering, mixing can be modeled using larger cells by specifying Rsw as a function of time
2. Residual/Capillary Trapping – CO2 captured in pore space
- CO2 moving through the reservoir will be trapped in rock pore space as a function of rock properties and hysteresis
- The volume of CO2 trapped is modelled in 6X by using residual gas saturation to scale both relative permeability and capillary pressure
3. Mineral Trapping – CO2 trapped in rock pore space as precipitate
- CO2 may be trapped as a solid precipitate in the rock as a function of rock mineralogy and rate of reaction
- The volume of precipitate and timing of precipitate formation is derived from laboratory data.
- The rate and volume of CO2 precipitation can be modelled in 6X using scripting and a dimensionless time function
4. Structural Trapping – Reservoir Seal
- Free CO2 migrates up until it accumulates as free gas just beneath the reservoir seal / caprock
- CO2 may dissolve rock through a CO2-Water-Rock chemical reaction, increasing porosity and permeability
- This CO2-Water-Rock interaction may eventually lead to seal deterioration and leakage
- The changes of porosity and permeability are derived from laboratory data and can be modelled in 6X using scripting and a dimensionless time function
