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

PANEL REPORT: SUBSURFACE CHARACTERIZATIONSUBSURFACE CHARACTERIZATIONCURRENT STATUSOverviewThe subsurface is spatially heterogeneous because of the complex geologic and biogeochemicalphenomena that create and modify subsurface materials and processes. Since the first well wasdrilled, design and management of resource recovery or emplacement systems has beenhampered by the difficulty of characterizing subsurface complexity. Consequently, predictions ofmass transport and reactions are often too uncertain to provide meaningful estimates of risks inthe contexts of human health, society, economics and the environment.Subsurface characterization is a broad topic that could be construed to encompass most of thetopics discussed in the other panel reports. The methods and research needs discussed hereinpertain to the entire subsurface, including the vadose zone, fresh groundwater systems and deepsaline systems. The panel focussed on those aspects of characterization that present the mostdifficult obstacles to progress in subsurface science and resource management:1. Measurement or estimation at the appropriate scales of state variables such as fluid pressure,temperature, solute concentration, and fluid saturation, and geologic media properties such aspermeability, porosity, capillary pressure or retention curves, geomechanical characteristics,and chemical reactivity. More effective subsurface characterization would not focus solely onthe usual point- or local-scale measurement of these attributes, but rather on larger scale ormultiscale measurements that might obviate the need for upscaling or downscaling, orprovide unprecedented reduction in model non-uniqueness (e.g., spatially continuousmeasurement of pressure and temperature, in situ measurement of field-scale reaction rateswith novel tracer methods).2. Understanding the interaction of physical fields, such as elastic waves or electromagneticdisturbances, with geologic media sufficiently to use these physical fields in multiscalecharacterization of the state variables and media properties. These interacting physical fieldsare complicated because small-scale properties of the medium influence the behavior of thefield at a much larger scale. Currently the theory that connects the small-scale properties tothe larger-scale field is inadequate for many characterization purposes.3. Fusion of disparate data types (e.g., geologic, geophysical, hydrologic, reservoir, biogeochemical)obtained at disparate scales to maximize reliability of characterization atappropriate scales. This hurdle requires substantial advances in forward modeling of couplednonlinear processes, joint inversion of coupled process models, and evaluation of cumulativeuncertainties stemming from local uncertainties contributed by each coupled model.4. Characterizing the extremes in fluid flow fields—namely, zones of preferential flow in whichfluids can migrate much faster than conventional estimates might suggest, and zones ofextremely slow fluid movement. The former would include conductive faults and wellconnectedfractures or sand/gravel bodies. The latter would include confining beds, aquitardsand seals. Because such preferential flow paths can be so consequential to material isolationefforts and exposure risk assessments, and because they are difficult to detect or anticipate,research focus on this area is paramount. Similarly, spatial structure and integrity of theBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 33