CO2 Sequestration
[Isoplanes; normal gradients/vectors]
How exactly to deduce a system of isoplanes; and normal gradients, vectors and traces of the planes, in the three-dimensional space, in a CO2 sequestration application, associated with a deep saline aquifer,
(A) towards predicting the behavior of CO2 and brine?
(B) towards deducing representative pathways along which CO2 would most likely to travel in 2 or 3 dimensions (with reference to the resulting gradients)?
(C) towards predicting CO2-brine contact planes/surfaces?
(D) towards deducing the orientations of the planes of constant potential energy for CO2 occurring within the 3-dimensional space of the aquifer? &
(E) towards deducing an overall movement of CO2 that finds its way into leakage pathways?
Suresh Kumar Govindarajan
Professor (HAG) IIT-Madras
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
24-July-2024
After CO₂ injection into a geological reservoir, the planes of constant pressure (isopressure planes) are generally expected to become non-horizontal. Here’s an explanation of why this happens:
1. Buoyant Nature of CO₂
- Density Differences: CO₂, when injected into a geological formation, is typically less dense than the formation fluids (e.g., brine). This difference in density causes CO₂ to rise within the reservoir due to buoyancy. The less dense CO₂ will move upwards, creating a pressure differential within the reservoir.
2. Formation of a CO₂ Plume
- Pressure Redistribution: As CO₂ is injected, it creates a high-pressure region around the injection well. The CO₂ plume, which is lighter than the surrounding fluids, will migrate upwards and spread out, creating a pressure front. This causes the pressure distribution to be non-uniform.
- Plume Shape: The shape of the CO₂ plume is typically dome-shaped or balloon-like due to buoyancy. As a result, the pressure at the top of the plume is generally higher than at the edges, leading to non-horizontal isopressure planes.
3. Pressure Changes Over Time
- Initial Injection: Immediately following injection, the isopressure planes near the injection well will be more steeply inclined. The pressure increases rapidly around the well and gradually decreases with distance from the injection point.
- Equilibrium State: Over time, as the CO₂ disperses and the pressure equilibrates, the isopressure planes will continue to reflect the buoyant rise of CO₂. The planes will not return to being horizontal due to the persistent buoyancy effects and the continued migration of CO₂.
4. Geological and Structural Factors
- Reservoir Structure: The presence of faults, fractures, and varying rock properties can further influence the pressure distribution. These geological features can create additional complexities in the pressure field, making isopressure planes even more non-horizontal.
- Cap Rock and Traps: The configuration of the cap rock and any geological traps can also affect the distribution of CO₂ and the resulting pressure planes. These features can lead to localized pressure variations and non-horizontal isopressure planes.
Summary
In conclusion, following CO₂ injection, the planes of constant pressure (isopressure planes) are expected to become non-horizontal due to the buoyant nature of CO₂. The pressure distribution is altered by the migration of CO₂, which rises due to its lower density compared to the formation fluids. The resulting isopressure planes reflect the uneven distribution of pressure within the reservoir, influenced by both the properties of CO₂ and the geological characteristics of the formation.
References
- Bachu, S., & Gunter, W. D. (2005). Sequestration of CO2 in geological media: A review of the technical feasibility, economic costs, and environmental impacts. Geological Society of America.
- IPCC (2005). Special Report on Carbon Dioxide Capture and Storage. Intergovernmental Panel on Climate Change.
- Metz, B., et al. (2005). IPCC Special Report on Carbon Dioxide Capture and Storage. Cambridge University Press.
- Scholz, C., et al. (2011). Geological storage of CO2. Geological Society of London.
These references provide insights into the dynamics of CO₂ injection and the resulting pressure changes within geological reservoirs.
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