Basic Research Needs for Geosciences - Energetics Meetings and ...

PANEL REPORT: MULTIPHASE FLUID TRANSPORT IN GEOLOGIC MEDIABuoyancy-driven flow at all scalesFor problems like CO 2 injection into deep brine-filled formations, the less-dense CO 2 is drivenupward by buoyancy. It is also driven laterally by pressure forces, and further influenced bycapillary forces associated with the small-scale fluid-fluid interfaces. While each of these drivingforces is reasonably well understood on its own, the interactions and interplay among these canlead to highly complex behavior, especially when the natural heterogeneity of a geologicalformation is included in the analysis.In such cases, new behavior and new characteristic time scales emerge as the macroscale CO 2 -brine interface interacts with heterogeneities in the permeability field. An example of these kindsof behaviors is presented in the sidebar on Buoyancy, capillarity, and heterogeneity: Buoyancydrivenflow at all scales. A suitable theoretical and computational framework for this behaviordoes not exist.Impact and coupling of interfacial phenomena and reactive flow at all scalesInterfaces between fluid pairs, and between fluids and solids, are fundamental to all multiphaseflow and reactive transport in geologic systems. A sound understanding of interfacial behavior,and how it is manifested across the range of length and time scales appropriate for practical flowproblems, remains an open question. Couplings between fluid movement and interfacialphenomena, such as precipitation/dissolution reactions and their feedback to the flow system,make modeling the system particularly challenging. Such couplings often manifest themselvesacross different scales. A comprehensive understanding of how behavior at one scale affectsbehavior at larger (and smaller) scales remains one of the most difficult challenges forunderstanding and predicting multiphase flow.Seamless transitions between mathematical descriptions of flow at multiple scales inheterogeneous media (pore level to basin scales)A grand challenge for multiphase flow in the subsurface is a satisfactory mathematicaldescription of behavior that is self-consistent across many length and time scales. Well-knownexamples include the transition from molecular statistical dynamics to the equations of fluidflow, such as the Navier-Stokes equations, and the transition from Navier-Stokes flow with anindividual pore to the Darcy equation at a laboratory column scale. Inclusion of multiple fluidphases and their associated interfaces leads to much more complex problems. Further transitionsfrom the core scale to the field scale introduce extreme challenges. Efforts to place multiphaseflow on a more rigorous foundation have begun, but much work is needed to develop these to thelevel needed. Intensifying the challenge still further is the effect of heterogeneous properties—chemical, interfacial, transport—across the wide range of length and time scales. Variations inproperties can trigger a number of important mechanisms that lead to different physical/chemicalphenomena impacting different parts of the geologic system at different times. Ideally, thisseamless transition framework will allow the scientific community to understand the emergenceof patterns, trends and behaviors at larger scales arising from behaviors at smaller scales.12 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems