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

PANEL REPORT: SUBSURFACE CHARACTERIZATIONThe issue of sensitivity is especially important for early identification of time-lapse changes inthe subsurface. Early identification of changes can be important for effectively managingsubsurface reservoirs. The capability to detect minute changes is also of importance for earlywarning and mitigation of natural hazards. In many monitoring problems, one seeks to detect aminute change in the properties. For example, if 1% of the CO 2 leaks from a sequestration site inone year, then 70% of the CO 2 will escape in a century. In this application it will be necessary tomonitor with a much smaller detection threshold than currently is possible. It is possible in thelaboratory to measure changes in the seismic velocity with an accuracy of about 0.01% usinginterferometric techniques (Snieder et al. 2002), but these accuracies cannot yet be achievedunder field conditions.BASIC SCIENCE CHALLENGES, OPPORTUNITIES AND RESEARCH NEEDSIntegrated characterization and modeling of complex geologic systems with largeand diverse data setsSubsurface geologic structures are complicated but not random. For sedimentary rocks, forexample, there is a wealth of data and models that relate sediment transport by rivers and oceancurrents to the mineralogy, texture, and large-scale structures of the resulting sedimentary rocks.Such geologic process descriptions can and must be used to develop better conceptual models ofsubsurface heterogeneity, including preferential flow paths and various scales of heterogeneitythat may be difficult to detect or represent with statistical methods. Such geologically informedmodels are also needed for determining the consequences of neglecting certain features inupscaled or more conventional models of heterogeneity. This is one strategy for defining whichsystem properties, attributes and scales are most relevant to a particular problem.The translation of geological processes into spatial patterns and scales of relevant properties(basin, formations, core scale) can be achieved using physical and numerical models ofdepositional, diagenetic and structural processes. The field of depositional process modeling isstill in the early stages, but with greater computational capability, and the optimal use andintegration of disparate data sets, it can evolve into a powerful predictive tool for the 3Dgeologic structures at various length scales, the microproperties that govern the bulk behavior,and the temporal evolution of these structures.One of the main challenges in creating a 3D scale-bridging description of geologic structures isto relate geophysical, geochemical and bio-geochemical measurements to in situ properties andprocesses. The relation between the measurements and the in situ properties is scale-dependentand needs to bridge different temporal and spatial scales. The quantification and reduction ofuncertainties play a special role because measurements and inferences from these measurementsare useless when the associated uncertainty is unacceptably large. The determination of therequired thresholds of uncertainties needs to be addressed. Ultimately, it is necessary to developa fundamental understanding of the relevant upscaling and downscaling laws for flow, transportproperties, reaction rates, and mechanical properties.44 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems