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

PRIORITY RESEARCH DIRECTION:DYNAMIC IMAGING OF FLOW AND TRANSPORT3. Methods are needed for measuring state variables such as pressure and temperaturecontinuously in space and time, rather than as local averages at points or within conventionalwell bores.4. To diagnose and image flow, transport, and reaction rates, it is necessary to understand muchbetter the interaction of physical fields, such as elastic waves or electromagnetic disturbanceswith fluid-filled porous media. This is especially important to advance our understanding ofrelevant upscaling and downscaling laws.This research will have spin-offs for optimal management of fluids in the subsurface, whichinclude waste disposal, enhanced oil recovery, and environmental remediation. Because of thefundamental nature of this research, much interaction with physics, chemistry and biology isenvisaged. Technical spin-offs include the continued development of miniature sensors anddistributed sensor networks. Because of the common importance of fluid transport, one may alsoexpect interactions with research and engineering in medical imaging and diagnostics.SUMMARY OF RESEARCH DIRECTIONTo design or evaluate facilities for waste storage and to assess the impacts of chemical spills,transport of injected fluids, or leaks of radionuclides on the subsurface environment, it isnecessary to measure and image subsurface physical and chemical properties that determine fluidflow, mass transport, and geochemical transformation. This is a difficult problem in geologicmedia because of the complex geometry and incompletely known history of subsurface rocksand sediments, as well as the high degree of spatial variability (heterogeneity) of the manyphysical and chemical properties. The variability is not simple because it is neither homogeneousnor statistically homogeneous. The variations are also, in general, neither random nor statisticallystationary. Instead, the properties appear to vary differently at different spatial scales ofmeasurement, so one often speaks of “multiscale heterogeneity,” and heterogeneity is viewed as“evolving,” in some sense, from the pore scale all the way to the basin scale. In reacting flowsactual heterogeneity evolves over time.In addition to the difficulty of characterizing an inaccessible, complex subsurface environment,research is limited by methods of measurement that are either confined to particular space ortime scales, or provide results that are only indirectly related to properties or processes ofinterest. For example, we can measure single values of average fluid pressure and temperaturewithin a control volume accessed by a well screen. These state variables measured at points inspace or over limited control volumes must typically be interpolated in space. More importantly,the interpretation of their meaning must be done with models that incompletely and non-uniquelydefine the multiple scales of properties or forcings that dictate the local values of the statevariables, which are also used to calibrate the models. Seismic velocities are an example. Theyare known to depend not only on the saturations and properties of phases present in the porespace, but also on the microscopic spatial distribution of the phases with the pores. A leapforward in both model calibration and our ability to observe complex phenomena in thesubsurface would be provided by new methods of measurement that span multiple space andtime scales, as well as better models for scale translation, as described in more detail in theGrand Challenges. Selker et al. (2006) provide an example of how spatially and temporallycontinuous measurement of temperature with fiber optics can open a new window into streamstreambeddynamics. It is time to start looking beyond traditional point measurements and to122 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems