Determining the Area of Review (AoR) in Carbon Capture and Storage: A tiered, probabilistic methodology to generate risk map

The effects and related risks to potable aquifers due to pressure increases and brine leakage through abandoned wells is a poorly understood phenomena and a potentially significant contributor to the risk profile in Geologic Carbon Capture and Storage. Numerical models are used to investigate the evolution of brine leakage (during and post-injection) through wells located in the region where plugged and abandoned (P&A) wellbores leakage could occur. This area, termed tier 3, builds on a 3-tier methodology to define the Area of Review (AoR) proposed by Birkholzer et al. (2013). This work, in conjunction with a quantitative assessment of tier 1 AoR (an area encompassing the CO2 plume) and tier 2 AoR (an are encompassing the extent where open well-bore brine leakage could occur), will lead to a quantitative understanding of potential risks and a metric for the complete spatial extent of environmental risk in Carbon Capture and Storage. Here, we develop a probabilistic methodology to generate "risk maps" related to tier 3 AoR. The risk maps are based on the premise that the two greatest sources of uncertainty in P&A leakage are 1) the location of the unknown well with respect to the injection well and 2) the permeability of the leaky P&A (which can span over several orders of magnitude). The methodology utilizes numerical simulations and probability theory to generate spatial distributions of risk, defined with no-impact or MCL thresholds. Probabilistic risk maps can be used to provide risk-based descriptions of the AoR to inform site selection and monitoring during and post-injection.