Q2. What are the conceptual geological settings that constitute the largest potential storage volumes?
The conceptual geological settings that constitute the largest potential storage volumes are (in decreasing potential capacity) deep saline reservoirs, depleted gas reservoirs, oil reservoirs (with and without enhanced oil recovery), and coal beds.
Q3. What are the main problems with the estimation of storage capacity?
Estimates of storage capacity must take into account the range of trapping mechanisms that are possible at each site, the different geological constraints on each mechanism, and the fact that different trapping mechanisms operate on different time scales that range from instantaneous to tens of thousands of years.
Q4. How does the author estimate the storage capacity of a geological reservoir?
Although in principle storage capacity estimation relies on a simple series of algorithms that depend on the storage mechanism under consideration to calculate the available capacity in a certain volume of sedimentary rock at a given depth, temperature and pressure, applying them to a specific region or site is complex.
Q5. What is the way to estimate the rate of injection of CO2?
If a site is of poor quality in terms of permeability (and thus can only accept small rates of injection), but has a lot of pore space and potential storage volume, then there will be a limit to the rate at which the CO2 can be injected for each well.
Q6. What is the definition of a realistic capacity assessment?
Viable capacity –is the capacity arrived at by also considering economic, legal and regulatory barriers to CO2 geological storage, and thus builds upon the realistic capacity assessment.
Q7. Why is it difficult to estimate the capacity of a geological reservoir?
It is particularly difficult due to the various trap types and trapping mechanisms that can occur, the different time frames over which trapping becomes effective, and the different physical states in which the CO2 might occur (Table 1).
Q8. Why are there so many errors in calculated storage capacity?
Many of the contradictory assessments and errors in calculated storage capacity are due to the desire or need to make quick assessments with limited or no data.
Q9. What is the effect of the migration rate of the CO2?
The efficiency of trapping for many of the mechanisms described in Table 1 depends upon the migration rate of the CO2, which itself is highly dependent on the rock and fluid properties and geological characteristics of each site.
Q10. What is the definition of the resource pyramid?
This version of the resource pyramid (Figure 3) attempts to represent the relationships between the reservoir quality and trap types (left vertical axis), trapping mechanisms (bottom axis) and the time that it takes until the trapping mechanism is effective (right horizontal axis).