Use of above-zone pressure data to locate and quantify leaks during carbon storage operations

We determine the potential accuracy in estimating the size and location of leaks in the caprock by history-matching above-zone pressure monitoring data to leakage models. The number of monitoring wells and the total monitoring time is varied in order to determine minimum pressure-monitoring requirements for effective leak characterization. The history-matching procedure uses particle swarm optimization to minimize the error between leakage-model solutions and synthetic observation data by adjusting model parameters governing the size and location of the leak, as well as the heterogeneous permeability field throughout the model. The method applies to storage projects with uncertain heterogeneous geology that may be described by a variogram model. Results from several examples indicate that as little as 6-12 months of above-zone pressure monitoring data, collected from at least 3 or 4 wells, may be sufficient to locate and estimate the size of a leak to inform mitigation and remediation strategies. No significant benefit is seen when using multilevel monitoring wells versus single-level monitoring wells. We also find that adding white noise to the synthetic observation data, with magnitude consistent with current pressure monitoring techniques, generally reduces error in solutions, likely due to a regularization effect. Taken in total, the results and procedures introduced in this study should be of use in designing monitoring strategies in large-scale carbon storage projects. (C) 2016 Elsevier Ltd. All rights reserved.