CO2 sequestration [Reservoir Hydrodynamics 01]
With CO2 and brine being mobile, and in the presence of a complex coupled forces between viscous, gravity and capillarity, whether, the resulting pressure gradient would remain oriented non-vertically?
Following CO2 injection, whether the planes of constant pressure (isopressure planes) would remain to be non-horizontal?
Despite the fluctuating levels of potential energy within the fluid body, would it still diminish in the direction of CO2 movement?
Whether CO2-brine interface would remain to be non-horizontal following CO2 injection? If so, then, would it remain tilted in the direction of CO2 movement or potential energy decrease?
Since buoyancy is the major force acting on CO2 within a hydrodynamic deep saline aquifer, can we still expect the potential energy minima to remain located at the highest point in the aquifer?
Under hydrodynamic conditions, whether, the factors causing CO2 trapping would remain to change markedly in terms of aquifer geometry, size and location of CO2-plume pools?
Whether, compactional squeeze or tectonic uplift would lead to increasingly strong hydrodynamic forces, following CO2 injection? In such cases, whether, CO2 would remain to be pushed farther and farther from structural trapping sites until they are totally displaced and the original CO2 trapping features would remain to be completely filled with flowing brine?
In CO2 sequestration application, in deep saline aquifers, whether, the maximum internal pressure gradient (the direction in which the rate of pressure increase remains to the greatest) would remain to be perfectly vertical – given the internal migration of CO2 and brine?
With buoyant force playing a critical role, in the early stages, whether, all the internal forces would remain orientated vertically?
Whether the CO2-brine fluid contacts would remain to be parallel to the isopotential traces and normal to the specific force vectors?
Feasible to reorganize the probable migration paths of CO2-phase; and feasible to predict the orientation of CO2-brine interfaces, if the levels of potential energy associated with moving formation brine are mapped?
Suresh Kumar Govindarajan
Professor (HAG) IIT-Madras
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
24-July-2024
The planes of constant pressure, or isopressure planes, in the context of CO₂ injection into a subsurface reservoir are influenced by several factors, including the density of CO₂, the geological properties of the reservoir, and the distribution of injected CO₂. Here’s a detailed explanation of how these factors impact the isopressure planes:
1. Density and Buoyancy of CO₂
CO₂ injected into a geological formation is typically less dense than the surrounding formation fluids (e.g., brine). As a result, CO₂ will tend to rise or migrate upward due to buoyancy. This buoyant force means that the pressure distribution in the reservoir will be affected by the vertical movement of CO₂. Consequently, the isopressure planes, which represent surfaces of constant pressure, are likely to become tilted or non-horizontal as CO₂ accumulates in certain areas.
2. Pressure Distribution and Reservoir Characteristics
- Initial Reservoir Conditions: Before injection, isopressure planes might be relatively horizontal, assuming the reservoir is in a state of hydrostatic equilibrium.
- During Injection: As CO₂ is injected, the pressure in the vicinity of the injection well increases. The injected CO₂ will initially create a high-pressure region around the wellbore. Over time, the pressure front will spread, causing a perturbation in the pressure field. If CO₂ is lighter than the formation fluids, the pressure will be higher near the injection point and lower as you move away vertically from the CO₂ plume.
3. Impact of CO₂ Migration
- Plume Shape: The shape of the CO₂ plume will affect pressure distribution. The CO₂ plume typically has a domed or balloon-like shape due to its buoyancy. This results in pressure increasing more rapidly closer to the top of the plume and less so towards the edges.
- Pressure Front Movement: As CO₂ migrates through the reservoir, it can encounter various geological formations, fault lines, or traps, which can influence the pressure distribution. These geological features can cause further tilting or warping of the isopressure planes.
4. Geological and Structural Considerations
- Reservoir Heterogeneity: Variations in rock permeability and porosity can lead to uneven distribution of CO₂ and pressure changes. High permeability zones may experience more significant pressure increases than low permeability zones, causing non-horizontal isopressure planes.
- Structural Traps: Faults and folds in the reservoir rock can also alter pressure distribution, causing deviations from horizontal isopressure planes.
Summary
After CO₂ injection, isopressure planes in a subsurface reservoir are generally expected to become non-horizontal. This is primarily due to the buoyant nature of CO₂, which causes it to migrate upwards and create a pressure differential. The pressure front, influenced by the density of CO₂, reservoir heterogeneity, and geological structures, results in a non-horizontal distribution of pressure in the reservoir.
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