Optimised Geophysical Survey Design for CO2 Monitoring – A Synthetic Study

Abstract

In this work, we evaluate strategies for design of fit-for-purpose geophysical survey layouts that allow acquisition of the minimum necessary amount of data while maintaining a sufficient level of resolution or accuracy of the subsurface parameters to be recovered. The objective is to determine the optimal survey layout for CO2 monitoring based on our, potentially limited, knowledge of the subsurface prior to data acquisition. The proposed method is based on the analysis of the eigenvalue spectrum of the data misfit Hessian. The spectrum provides a simple and intuitive means to evaluate and compare the quality of given survey designs. Examples from seismic and EM monitoring are included. We perform synthetic studies and assess whether a sequential experimental design can be used to determine if only a small amount of data is sufficient to achieve comparable resolution to when the comprehensive dataset is used. Comparisons between random and optimal data subset selection are performed. The results suggest that the method is quite robust with respect to the starting model used for the analysis. The method offers a powerful means to acquire enough information at a minimal cost and analyse the pattern of the optimal acquisition design for a given tomographic method.

Keywords: Survey design, CO2 monitoring, CSEM, FWI, Monitoring technologies and techniques, GHGT-14