Tenth Year Annual Report:
Carbon Storage: Active and Integrated Management of Injection Operations
Celia and colleagues have also begun to investigate a range of possible activities synergistic to CO2 injection operations. Most of them involve brine production and possible reinjection, and are placed within a broad framework in which the reservoir would be managed much more actively. Possible benefits from such an active management approach include:
- reduced reliance on surface water for power plant operations
- improved control of reservoir flows and enhanced options for remediation
- reduction in the area of review for a given operation
- possible use of heat contained in extracted brine
- use of cooled (extracted) water for plant operations
These benefits could be important under a number of different scenarios, including operations in water-limited regions of the world, operations where increased public acceptance is important, and operations that may be limited by maximum injection pressure constraints.
Figure 15 shows some of the basic ideas involved in this active management approach. Rather than a single injection well, multiple wells would be installed, giving many more operational options for the system. As an example, Figure 16 shows the impact of pressure control at different distances from the injection well, assuming a constant rate of injection determined by reaching 90% of fracture pressure for passive injection. The closer the extraction wells are placed to the point of injection, the smaller the pressure increase seen at the injection well as CO2 is pumped into the aquifer. This reduction in pressure provides opportunities for significantly larger injection rates that can be modified and optimized as a function of time. However, the smaller distance between injection and extraction wells also leads to potential breakthrough of the CO2 at the extraction well. While some wells may be placed close to injectors for the dual purpose of early pressure control and monitoring of the timing of breakthrough, in general breakthrough would probably not be desirable.
Active management could also have benefits that would favorably impact public perception of CCS. For example, use of extracted brine to drive a district heating system for a community, or provision of additional water after desalination, even if it is gray water, can change the operation from one with no benefit to the local community to one with significant benefits. For these and other reasons, the group is pursuing a much more detailed analysis of these ideas of active management.