Framing Monitoring Needs to Detect Leakage from Wells to the Overburden

In this study we correlate monitoring thresholds and chemical changes in underground sources of drinking water chemistry from the leakage of storage reservoir fluids using synthetic data. The geologic scenario is based on geology and legacy well locations near Kimberlina California, USA. The modeled scenario is an ideal site for potential CO2 storage in many respects because the legacy well is significantly far from the injection location, and the simulated leakage produces modest volumes of impacted groundwater. We assess the sensitivity of magnetotellurics (MT) to changes in groundwater chemistry as a function of depth and plume volume. The results show the importance of monitoring all permeable units to increase the likelihood of detecting and mitigating a leak as soon as possible, rather than monitoring only above the cap rock. Sensitive methods would be needed to detect the modest plumes that were simulated based on the Kimberlina geology, however MT could be used to detect more aggressive leaks with much higher TDS changes and larger volumes. (C) 2017 The Authors. Published by Elsevier Ltd.