Merits of pressure and geochemical data as indicators of CO2/brine leakage into a heterogeneous, sedimentary aquifer

This study assesses the merits of pressure data and geochemical data as indicators of a combined CO2/brine leakage into a heterogeneous, sedimentary aquifer. We simulate the changes in three aquifer responses (pressure, total dissolved solids (TDS), and pH) due to CO2/brine leakage at an abandoned well with an uncertain location and hypothesize that these changes can only be observed from a single shallow monitoring well, mimicking the low density of observation wells for the considered aquifer. Specifically, detection likelihoods are calculated to describe how frequently pressure, TDS, and pH signals will coincide with a leak for observations made at different distances and times from the initiation of the CO2/brine leakage rate. The pressure signal gives a more spatially extensive signal than either TDS or pH, and pressure detection probabilities increase upstream of flow barriers (pressurizing-affect). The pH and TDS rebound down-stream of the flow barriers. When only considering the samples that experience the highest leakage volumes, there is a 50% likelihood of detecting a pressure change 400 m away at times ≥30 years. However, the TDS and pH detection likelihoods are <20% at 100 m distance for times ≥30 years.