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

PANEL REPORT: MULTIPHASE FLUID TRANSPORT IN GEOLOGIC MEDIAFigure 3. Schematic (left) illustrates the chemical processes associated with the microbial-mediated reduction ofiron in solution in the presence of CO 2 . The SEM (right) of a large siderite (FeCO 3 ) crystal co-precipitated withfine-grained magnetite in a bicarbonate-rich culture of iron-reducing thermophilic bacteria at 65 ° C (from Zhang etal. 2001).methanogens are concentrated in sandstones (McMahon and Chapelle 1991; Fredrickson et al.1997; Krumholz et al. 1997). Subsurface injection of CO 2 can impact this lethargic subsurfacemicrobial ecosystem in a variety of ways, not the least of which could include iron reductionleading to biomineralization (Figure 3). For example, the mobilization of dissolved organicmatter, as observed in the CO 2 injection into the Frio Formation (Kharaka et al. 2006a), mayincrease its availability for fermentation reactions; the increase in dissolved CO 2 may enablebiogenic CH 4 formation; the decrease in pH may favor release of critical nutrients (e.g.,phosphate and metals) and elevate cell membrane H + gradients, both of which promote cellgrowth and activity.The rates and extent of microbial immobilization of CO 2 , however, are difficult to predict sinceour knowledge of anaerobic microbial processes both in lab and field is based upon studies ofwater-saturated systems, not a mixed CO 2 /water system at high pressure (Zatsepina et al. 2004).The challenge will be to parameterize this process at a scale that is useful for field-scaleapplications, based on comparison of laboratory microbial transformation of CO 2 under highpartial CO 2 pressure in the presence of brine and various mineral/rock media for a range ofmicrobial phenotypes with field observations.Shallow crustal deformation and fluid flow driven by large anthropogenicperturbationsUnderstanding the physical and chemical responses of subsurface rock masses to large-scaleperturbations like those associated with CO 2 injection presents substantial scientific challenges.Rock masses are highly heterogeneous with regard to lithology, texture, structure and strength.Discontinuities such as faults, joints and microfractures exist at all length scales, and they havesignificant impact on the coupled rheological and transport responses, which may be highlynonlinear and anisotropic. If other injection environments are considered, such as poorly lithified16 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems