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

PRIORITY RESEARCH DIRECTION: TRANSPORT PROPERTIES AND IN SITU CHARACTERIZATIONOF FLUID TRAPPING, ISOLATION, AND IMMOBILIZATIONTRANSPORT PROPERTIES AND IN SITU CHARACTERIZATION OFFLUID TRAPPING, ISOLATION, AND IMMOBILIZATIONABSTRACTImmobilization of fluids within pores and/or beneath impermeable stratigraphic intervalsdominates a range of natural processes within the earth’s crust, including the migration of fluidsalong fault zones, the creation and maintenance of natural geothermal systems, the emplacementof ore deposits, and the trapping of hydrocarbons. Fluid immobilization is also the single mostimportant factor for assessing a proposed geologic CO 2 storage location. However, our currentstate of knowledge about fluid-trapping mechanisms and the flow properties of slow/nopermeability intervals (seals), faults, and fractures under in situ conditions is limited, as is ourability to measure and characterize the spatial and temporal variations in the trappingmechanisms operating within a reservoir. Ground-breaking improvements in quantifying therelevant pore-scale physics, slow chemistry, response to pressure and fluid evolution, and remotemeasurement of mineralization and other changes in rock pores will lend needed insight intonatural processes and ensure the success of large-scale energy byproduct storage.EXECUTIVE SUMMARYVarious mechanisms play a role in the immobilization of radionuclides and fluids within theEarth. Mechanisms include trapping of fluids by geologic seals in the form of impermeable strataor faults, deposition of minerals due to interactions of fluids with rocks, formation of bubbleswithin rock pores that inhibit the migration of fluids, density differences between pore fluids thatprevent one fluid from moving above or beyond another, and the sorption of radionuclides to thesurfaces of fractures. These mechanisms interact with each other at different temporal and spatialscales. However, the operable mechanisms and the interplay among them are poorly understoodeven in the laboratory, and are virtually unknown under in situ conditions. For example,mineralization is expected to occur by interaction between dissolved CO 2 and local mineralphases. While there is a general agreement on the process, the conditions under whichmineralization will occur, and the rate at which it will occur, are largely unknown. Asmineralization occurs, the resulting changes in porosity may cause changes in the flow regimewithin a region and change or alter immobilization processes at nearby locations. Detecting suchchanges using remote imaging techniques is crucial for the effective management of fluids andthe chemistry of what they carry in the subsurface.Even small aperture flaws in a seal or the spatial variation in the immobilization mechanism canallow rapid fluid transport. The injection or natural infusion of fluids into a zone can haveprofound impact on the state of the surrounding rock, altering its trapping ability. Figure 41depicts a situation in which the injection of fluids alters the local stress field that may lead toinstability within surrounding strata. Figure 42 shows a field example where the occurrence of anearthquake caused significant changes in productivity due to the likely changes in pore fluidflowprocesses in a reservoir. This reveals the sensitivity of fluid flow and possible fluidmobilization mechanisms to small changes in externally applied reservoir conditions.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 131