Shale reactivity and consequences for long term stability of CO2 storage

Increasing atmospheric concentrations of greenhouse gases are expected to cause a gradual warming of the Earth's surface leading to potentially disastrous changes to the global climate. This is an international concern, as well as an international respons ibility, and several research programs in Norway and USA are addressing this problem. It is important to combine research efforts and establish international collaborations. An important aspect of this project is therefore to establish mutually beneficial research collaboration between University of Bergen and Los Alamos National Laboratory while at the same time addressing important issues related to long term stability of aquifer storage of CO2. Once CO2 is injected, it will start to migrate as an immis cible gas or supercritical fluid, and accumulate beneath low-permeable structural features. Reactions among supercritical CO2, brine, and the clay-rich caprock may give rise to a number of consequences of geochemical and geotechnical significance. Reacti ons that exhibit negative volume changes may produce high permeability channels, concomitant loss of integrity of the system, and subsequent release of CO2. Alternatively, reactions in the shale may yield mineral assemblages that fill porosity and decreas e permeability due to positive volume change or transport of reactive components from the aquifer into the shale. In addition to the potentially positive aspects of porosity decreases, such changes may result in enhanced brittle character relative to pred ecessor mineral assemblages, and consequent failure modes. Competency contrasts may develop between a carapace of reacted material overlying supercritical CO2 zones and the unreacted periphery of the shale. Fracturing, loss of system integrity, and moveme nt of CO2 may result. Reactions that exhibit positive volume changes and reactive chemical transport may, in other cases, produce self-healing fractures.