A feasibility study of CO2 sequestration monitoring using the mCSEM method at a deep brine aquifer in a shallow sea

Abstract

Reservoir production monitoring using marine controlled-source electromagnetic (mCSEM) has been studied recently because it is sensitive to resistivity changes resulting from variations in hydrocarbon saturation. However, mCSEM for [Formula: see text] sequestration monitoring has scarcely been investigated, although the mCSEM method is advantageous for monitoring [Formula: see text] injection and migration. To investigate the feasibility of mCSEM monitoring for [Formula: see text] sequestration, we conducted numerical experiments of representative [Formula: see text] injection models at a deep brine aquifer in a shallow sea. By using a modified secondary field method, we effectively address the airwave problem occurring when mCSEM is applied to a target beneath a shallow sea. We demonstrate the modified secondary field method can restore high frequency band data, which is beneficial for the detection of the movement of injected [Formula: see text]. Furthermore, using a modified scattered field approach for 2.5D forward modeling, we achieve very high accuracy, which is essential for the simulation of electromagnetic fields generated by [Formula: see text] injection in a deep brine aquifer. The mCSEM response, which is enhanced by the modified secondary field method, shows small but measurable changes in a given pseudorealistic [Formula: see text] sequestration scenario. The mCSEM responses differ for horizontal and vertical injections. These results include the feasibility of applying mCSEM to [Formula: see text] sequestration monitoring. Optimum operating frequency bands and source-receiver geometries for a brine aquifer model beneath a shallow sea are proposed based on the results of the numerical experiments. Moreover, we suggest the necessity of various types of data acquisition for the monitoring of a [Formula: see text] plume based on analyses of multiple components of electric and magnetic fields.