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

PRIORITY RESEARCH DIRECTION:DYNAMIC IMAGING OF FLOW AND TRANSPORTimportant geochemical characteristics of rock formations. For example, redox-sensitive solutescould gage the reductive or oxidative characteristics of a formation, thus providing importantinformation for modeling transport of many contaminants. In the long term, sophisticated tracerscould be developed that target specific characteristics of formations. Solutes that chelate specificelements and solutes that transform over different time scales under different conditions could beused to collect detailed information along a flow path that is then “delivered” to a sampling wellwhere the solutes are retrieved.Nonreactive tracers that can identify flow paths may be derived based on the emergingdevelopments in the field of nanotechnology. Such tracers would be sufficiently small to movefreely through a formation while communicating their positions and, possibly, measuredvariables to an observer. Such information might be propagated by releasing a continuous streamof nanobodies and having such bodies communicate with each other in an organized manner.The result could provide much more detail concerning the geometry of flow paths throughgeologic media, and vital mixing information.Ultimately, it might be possible to attach microscopic measurement devices to microbes. Whenthese microbes are (bio)engineered to move in specific spatial patterns, for example by followingchemical gradients, they could be used as a transportation vehicle. By tapping into chemicalpotentials, the metabolism of these microbes could potentially be used as a power source for thesensor.Groundwater age distributionThe molecules within a water sample from the subsurface have a distribution of ages that canrange widely (e.g., years to centuries, or decades to millennia) and that is diagnostic of the fluidflow history, including flow pathways, sources of the fluid, dispersion, characteristics,preferential flow and leakage from adjacent media—all happening at the relevant multiple spaceand time scales. Data on groundwater age distribution within fluid samples therefore can betremendously powerful for characterization and for calibrating or validating multiscale flow andtransport models. The distribution of groundwater ages within a fluid sample, however, cannotbe measured directly at present. It can only be inferred from models, and vaguely defined by avery limited set of age-dating tools.Environmental tracer technologies currently exist to estimate residence times over time scales ofabout 0 to 50 years and over time scales of about 10 3 to 10 5 years, but there remains afundamental gap in dating tools over time scales of 50 to ~3000 years (Figure 40). While severaltracers could theoretically fill this gap (e.g., 39 Ar), advances in measurement technologies arestill needed due to the very low concentrations of such tracers in natural waters. Suites of tracersthat respond to various travel times are needed to resolve the travel time distribution. Bymeasuring both mean and travel time distributions, an integrated characterization of flow rates,storage volumes, and mixing processes could be obtained with the help of flow and transportmodels.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 127