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

PRIORITY RESEARCH DIRECTION:DYNAMIC IMAGING OF FLOW AND TRANSPORTDYNAMIC IMAGING OF FLOW AND TRANSPORTABSTRACTManaging waste and resources in the subsurface critically depends on predictions of fluid flow,mass transport and reaction rates. Our current capabilities to measure these phenomena andproperties are extremely limited, especially in situ. To develop the capability for dynamicimaging of flow, transport and reactions, it is necessary to measure state variables continuouslyin space and time, rather than locally or at fixed scales. This needs smart tracers that are capableof relaying their locations and concentrations remotely, or providing chemical reaction rates atthe appropriate scales. Improved resolution in space and time measurements of phase saturations,new means of estimating groundwater age distributions within individual fluid samples, andbetter understanding of the interaction of physical fields with fluid-filled porous media on avariety of length scales are all required.EXECUTIVE SUMMARYWaste disposal, environmental remediation, and the efficient exploration, production, andmanagement of the earth’s resources depend critically on the migration of fluids in thesubsurface, and the geochemical reactions that occur in the subsurface. Presently, some of theproperties and processes can be measured in the laboratory or in situ, but current science andtechnology is not sufficiently far advanced to measure certain properties in situ at depth. Openquestions exist in the details of the transport of multiphase reactive flow in porous media thatcannot be addressed adequately even at the laboratory scale because of a lack of adequatediagnostic methods.Subsurface science used to predict behavior of transport processes is based on local values ofstate variables (e.g., pressure, temperature, concentration, phase saturations) in heterogeneousmedia. Models of those media used to make predictions typically are not sufficiently constrainedby local measurements. As a result, the models are non-unique and are typically considered moreappropriate for hypothetical analysis than for bona fide prediction. In situ, multiscalemeasurement of state variables, flow, transport, fluid age, and reaction rates would dramaticallyimprove both our understanding of subsurface fluid processes and our ability to producepredictive models.Research is needed in four areas to make further progress:1. There is wide scope for the development of smart tracers. These can be chemical tracers(active or conservative), reactive tracers whose presence, or state, can be probed withphysical fields (e.g., organo-metallic tracers), or miniature sensors that can be distributedthrough the subsurface. Coupling these tracers to microbes as a transportation vehicle, oreven as a source of energy, might create new opportunities.2. Measured or estimated fluid age distributions within individual fluid samples would providea leap forward in our ability to characterize fluid flow pathways, rates, sources and multiscaledispersion, and to create predictive models of local-to-regional scale flow and transport. Keybreakthroughs in the science of environmental tracers are needed to make this happen,particularly concerning our current inability to reliably date fluids in the 50–3000 year range.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 121