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

PANEL REPORT: SUBSURFACE CHARACTERIZATION“slow” media are critical for containment and management of subsurface resources and are aprimary reason why extraction of fluids, whether petroleum or contaminated groundwater,tends to be difficult and inefficient.5. Remote observation of fluid flow, mass transport, fluid residence time, and reactions.Characterization of the complex subsurface is most hampered by its inaccessibility. We canachieve greater access to the subsurface by drilling more and more boreholes, but this is veryexpensive, typically not adequate, and is counterproductive when the objective is to maintaina naturally well-sealed storage site. Revolutionary change in our ability to characterize thesubsurface will most likely come from techniques that provide much greater access with lessdependence on drilling. Such techniques might include “smart” tracers capable of relayingtheir position without being sampled directly, the ability to measure local fluid residence timedistribution (fluid age distribution) as a direct indicator of dispersion and preferential flow,enhanced geophysics including fusion with other data types (see Item 3 above), and theability to monitor dynamic subsurface fluid processes remotely.These obstacles can be organized under four broad, overlapping areas:• Integrated characterization and modeling of complex geologic systems with large and diversedata sets• In situ characterization of fluid trapping, isolation and immobilization• Imaging flow, transport and chemical attributes• Monitoring dynamic subsurface processes associated with large-scale anthropogenicmanipulationsIntegrated characterization and modeling of complex geologic systems with largeand diverse data setsModern problems of coupled flow, transport and reaction require better coupled models, bothforward and inverse, for resolving not only the dynamic phenomena but also for resolving thecharacterizations of spatial-temporal variations in relevant variables. In other words, moreunified modeling approaches not only provide the means of simulating the relevant, coupled,nonlinear phenomena, but also potentially provide the means for better characterization throughapproaches such as joint inversion. No single data type (e.g., geologic, geophysical, hydrologic,geochemical, geomechanical) is sufficient by itself to characterize the complex subsurface. Thisis true even if one were trying to characterize only one aspect, for example, physicalheterogeneity. Just as human perception of a 3D object requires observations from multipleperspectives, the complex subsurface can be better characterized by observing how the systemcomplexity manifests through all the available physical and biogeochemical signals.Current modeling practices decouple both scale and physics, and integrate data, in an ad hocmanner (Hill and Tiedeman 2007). A rigorous paradigm for treating these problems in thegeosciences is missing. This is critical because incorrect treatment may lead to a grossaccumulation of errors due to strong nonlinear couplings. Such strong nonlinearities arefrequently encountered in multiphase flow, reactive transport, and geomechanics, although the34 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems