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

GRAND CHALLENGE: SIMULATION OF MULTISCALE GEOLOGIC SYSTEMS FOR ULTRA-LONG TIMESscales. For example, injection of fluids into the subsurface affects not only fluid pressures withinthe reservoir, but can result in deformation of the rock that affects permeability throughpore/fracture closure or opening, the initiation of chemical reactions that result in dissolutionand/or precipitation of minerals, the enhancement/death of microbial life, the simultaneous flowof different fluid components and phases resulting in fluid fingering from viscous, capillary,gravity and thermal forces. Geologic storage of CO 2 generates buoyancy forces that act on allscales, producing potentially simultaneous pore-scale, reservoir-scale and basin-scale effects.Simulation of leakage from repository sites will require predicting flow paths and geochemicalreactivity at low hydraulic gradients and low concentrations. Heterogeneity, multiphaseinterfacial and phase interference effects, and geochemical reactions add further complexity tothe system and demand advances in understanding and modeling capability. Advances can beachieved through development of a seamless, multiscale framework for modeling coupledmultiphysics processes in heterogeneous systems.Thus the fundamental challenge for model simulation of subsurface processes is accuraterepresentation of physical processes, not only at specific scales but also across scales. Thedevelopment of general stochastic mathematical and numerical frameworks of large-scaledynamic nonlinear systems is needed to rigorously quantify the uncertainties and risks associatedwith site selection, operation, and long-term monitoring of large-scale subsurface storageprojects. The fundamental importance of heterogeneity on all scales in natural systems suggeststhat research in this area will have broad scientific impact on subsurface science. The primaryimpact on technology is the development of multiphysics simulation capabilities that offerseamless modeling of processes over multiple scales. From the improved forecasting of longtermfate of sequestered materials will come numerous improvements in applications, such asdesign and optimization of injection and storage strategies, monitoring programs, remediationtechniques, and risk assessment.SCIENTIFIC CHALLENGESThe subsurface is composed of a hierarchy of structures and processes that span a wide spectrumof length and time scales (Figure 36). Any subsurface response is a function of this dynamicmultiscale spectrum, which includes reinforcing and damping feedbacks of a variety of strengths.Important feedbacks are often those that traverse scales. Multiscale modeling is necessary tocorrectly represent the dynamic evolution of the geologic system. Modeling requires the parsingof behaviors and interactions observed at microscales to define the response at the field scale.These behaviors are controlled by transport mechanisms driven by a complex interplay ofviscous, capillary, gravitational, inertial, reactive, diffusive, geochemical, biological andgeomechanical forces.Flow of multicomponent, multiphase fluids, such as mixtures of CO 2 and brines, is poorlyunderstood when buoyancy is the dominant driving force. The instabilities inherent in buoyantflow are well known, but when the fluids occupy a porous medium, new behavior and newcharacteristic time scales emerge at the pore scale, and as interfaces interact with heterogeneitiesin the permeability field. Because capillary forces often exceed buoyancy forces in geologicsystems, still more complicated behavior emerges as fluid interfaces encounter heterogeneities inthe capillary pressure characteristics of the domain. A suitable theoretical and computationalframework for multiscale buoyancy-driven flow remains an outstanding challenge.96 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems