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

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTFigure 6. Conceptual risk profile of a geological carbon sequestration site. Vertical axis isleakage risk. Overall, risk decreases dramatically post-injection and then more gradually.Courtesy of S. Benson 2006.manifestation. In addition, rapid mineral dissolution and release of metals and volatile organiccompounds may result from such leakage (e.g., Kharaka et al. 2006). Cement carbonation aroundwellbores can change physical and rheological properties (e.g., Carey et al. 2006). Aging,corrosion, and shifting of completion materials can cause leaks (IEA GHG 2006), andmechanical well failure by shear on bedding and fault planes presents a real hazard to long-termoperations and storage effectiveness (Bruno 2001).Wells in CO 2 -enhanced oil recovery areas do not appear to have high failure rates, and manytechnologies exist to plug and mitigate leakage even from major well failures (e.g., Lynch et al.1985). However, “sweet” corrosion (no sulfur) and an increased incidence of blowouts in CO 2 -enhanced oil recovery areas have grown as concerns over the last 10 years (Skinner 2003),although there are proactive operational measures to prevent and mitigate CO 2 blowouts. Ingeneral, the reported events generally have not received scientific study, and it is possible thatprocesses with long time-scale effects (e.g., well-bore corrosion) have not yet reached keythresholds. Major issues that will need to be considered are location and construction of existingwells, methods used to seal old wells, availability of methods to seal surface leaks, and theatmospheric risk associated with releases as a function of location and weather conditions (e.g.,Bogen et al. 2006).Substantial uncertainty remains around the nature of the long-term wellbore environment atdepth, the presence and stability of fractures within formations near wells, the condition anddistribution of cement around well casings, and the static and dynamic relationships betweenrock, casing, cement, and plugs (IEA GHG 2006). Key processes remain poorly parameterized,such as the degree and nature of formation damage in the wellbore environment, the bondingprocess, and permeability dynamics in CO 2 -rock-brine-casing-cement systems.Appendix 1 • 20Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems