Tenth Year Annual Report:
Carbon Storage: Future Plans
The experimental work on indentation and diffusivity of corroded paste has been completed. This concludes the Scherer group's study of cement corrosion, as sufficient data will have been obtained to permit analysis of leakage with dynaflow.
Leaky Wells and Discrete Fracture Networks
Future work of the Prévost Group will be on extending the dynaflow reservoir simulation toolbox by adding a method for simulating leaky wells and faults that provide preferential leakage paths. Coupling between fluid flow in faults and geomechanics will also have to include the possibility of slippage along faults. Also, further work will be done to improve the compositional aspects of the simulator, in particular in modeling boiling of CO2 as it moves from the storage formation to the surface in a leakage scenario.
Simplified Models for CO2 Injection, Migration, and Leakage
The Celia Group is in the process of building a hierarchical set of models that span a wide range of different situations. For example, the simplest models are for a single formation bounded above and below by impermeable caprocks, with large lateral extent, and fairly uniform properties. In this case a range of analytical solutions can be used (See http://monty.princeton.edu/CO2Interface/) . Next are systems with caprock that have either localized leakage pathways (wells or faults/fractures) or allow for diffuse leakage but still have small enough pores to exclude (by capillary forces) the CO2. These models range from semianalytical to numerical, with numerical models including a range of possible geometric and parametric heterogeneities as well as capillary and dissolution trapping. Next are models that have sufficiently permeable and porous caprocks to allow diffuse leakage of both brine and CO2, but where the permeability contrast between the formation and the caprock is large enough to make flows in the caprock essentially vertical. Models of this type also allow many kinds of heterogeneities and many different kinds of processes, but still allow for directional separation and therefore model efficiencies. The final model type is a full three-dimensional model where scale or directional separation is not applicable.
For all of these models, the researchers seek multi-scale representations where all of the important features and characteristics of the system can be incorporated systematically into the model descriptions. The resulting set of multi-scale governing equations is almost always easier to solve than the fully-resolved three-dimensional system. The group's goal is to have a suite of modeling options that can be applied to the variety of systems expected to be encountered in the field, with software that is sufficiently developed that many of the computational details become transparent to the user.
Active and Integrated Management of Injection Operations
The Celia Group will also continue to develop analyses of brine extraction and reinjection, with a focus on subsurface impacts and on possible synergistic uses at the land surface. These include the economics of desalination, including identification of salinity limits; analysis of heat extraction and possible uses of heat rejected from the extracted brine, with an initial focus on possible district heating/cooling systems; possible agricultural and other uses for gray water associated with partial desalination; and analysis of cooling demands at CCS power plants and the impacts of water demand on those requirements.
This work is linked to ongoing modeling work through inclusion, in the models, of brine extraction and injection wells, and through the investigation of the impacts that different forms of capillary pressure and relative permeability functions have on plume shape and transport, which is important for analysis of breakthrough at production wells. The overall initial goal is to determine whether brine extraction and the broad ideas of active reservoir management make sense in terms of reduced risks, smaller areas of review, and synergistic resource uses at the land surface.
Molecular Simulation of CO2 Hydrates
In understanding hydrate nucleation, insights into the formation of the critical hydrate nucleus are of primary importance. Pablo Debenedetti and colleagues aim to implement the advanced sampling technique known as forward flux sampling to study CO2 hydrate formation over broad ranges of temperature, pressure and salinity to identify the characteristics of the critical nucleus for CO2 hydrate formation and estimate the associated nucleation rates under conditions relevant to carbon capture and storage. These studies will then be extended to evaluate the effect of confinement on kinetics of CO2 hydrate formation.
Molecular Dynamics Study of Heterogeneous Ice Nucleation
Field and laboratory experiments indicate that the presence of mineral dust and organic particles affect both the freezing temperature of water and the rate of freezing, which can have a strong impact on cloud microphysics. Interestingly, studies indicate that while illite, kaolinite, and montomorillonite efficiently nucleate ice, quartz and calcite are poor ice nuclei. In addition, the ice nucleating efficiency of these surfaces is temperature-dependent. While a growing number of field and laboratory studies are providing much needed information on heterogeneous ice nucleation relevant to cloud formation, the principles underlying the reasons why some minerals are better ice nuclei than others are poorly understood. This understanding is important to parameterize and develop weather and climate models.
The Debenedetti group plans to implement a recently developed technique called forward flux sampling to study ice formation in the presence of mineral dust surfaces. Using this technique, they can generate a statistically significant number of molecularly detailed trajectories of the transition from water to ice on various surfaces and calculate the rate of ice nucleation. The ability to tune the surface-water interactions (i.e., chemistry) while retaining the surface topography in simulations enables us to decouple the effects of surface chemistry and topography on ice nucleation, and to provide guidelines to parameterize ice nucleation and growth on different surfaces at atmospherically-relevant conditions.