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

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTTable 3: CO 2 properties at likely injection conditionsCO 2 property Likely minimum T(35°C) and P (8 MPa)Likely maximum T(80°C) and P (40 MPa)Density: kg/m 3 419 823Viscosity: mPa/s 0.030 0.076Solubility: weight % in fresh water(wt.% in 50,000 ppm TDS water)5.2% (4.1%) 5.8% (4.7%)Data from NIST chemistry webbook (http://webbook.nist.gov/chemistry/fluid/) and Spycher andPruess (2005).Over time, injected CO 2 remains within the target reservoir and will dissolve and react with thelocal rock volume (see below). If CO 2 leaks from the reservoir, it will migrate towards thesurface and will change phase from supercritical fluid to gas at approximately 800 m depth. Thegas phase will expand and cool. At very high rates of ascent, Joule-Thomson cooling of CO 2could be sufficient to solidify the CO 2 and either plug or divert flow temporarily (Pruess 2006).Though this is unlikely under most geological conditions of interest, it may be important in thewell bore or near-well environment.Substantial process uncertainties remain in how CO 2 interacts with other pore fluids. Forexample, uncertainties persist in how CO 2 interacts and mixes with gas, water, and oil in thesame pore. Changes in solubility, equations of state, dynamic composition, fluid properties, andinterfacial tension make it difficult to predict sweep, dissolution rate, and mixing fronttrajectories (e.g., Stalkup 1987; Jessen et al. 1998; Yang et al. 2005). Initial modeling work hasexplored how the introduction of CO 2 might affect existing subsurface microbial communities(e.g., Onstott et al. 2005). Enhanced microbial activity could lead to the development of biofilms,which could reduce pore and fracture permeability. These uncertainties ultimately affectquestions of CO 2 fate, and the rates and importance of other pore-scale processes (e.g., dryingand salting of intra-pore brines). Focus on some of these questions would lead to improvedsimulations and predictive capabilities.Trapping mechanismsA number of geological reservoirs appear to have the potential to store many 100’s–1000’s of Gtof CO 2 (Benson and Cook 2005). The most promising reservoirs are porous and permeable rockbodies at depth (Figure 2).Saline formations contain brine in their pore volumes, commonly with salinities greater than10,000 ppm.Depleted oil and gas fields have some combination of water and hydrocarbons in their porevolumes. In some cases, economic gains can be achieved through enhanced oil recovery orenhanced gas recovery (Stevens 1999; Oldenburg et al. 2004; Jarrell et al. 2002). SubstantialCO 2 -enhanced oil recovery already occurs in the US with both natural and anthropogenic CO 2 .These fields provide much of the knowledge base we have about the potential issues related toCO 2 sequestration. Although oil and gas fields have the broadest knowledge base, they are alsoalready breached by all of the oil and gas wells that have made them economic, but potentiallyprovide leakage pathways.Appendix 1 • 8Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems