Revealing the surface deformation induced by deep CO2 injection in vegetated/agricultural areas: The combination of corner-reflectors, reservoir simulations and spatio-temporal statistics

The performance of Permanent Scatterers PS Interferometry (PSI) analysis is highly limited where the presence of large vegetated cover (agricultural terrains/forests) reduces signal coherence. A possible solution relies on the installation on ground of artificial devices (Corner Reflectors CR) to complement the existing PS network. Yet, the number of such CRs (spatial density typically ~ 1/km2) can be limited when the deformation pattern affects a large area (tens of km2) especially for CO2 geological storage in open aquifers. In order to support the surveillance of such sites, we address here the question of how to estimate the spatio-temporal distribution of the ground displacements over the whole area using only the sparse CR + PS network. We propose to test the feasibility of the Geostatistics Output Perturbation (GOP) method, enabling to combine: 1. The results of the reservoir model calibrated on the limited number of ground displacements' time series and, 2. The spatial correlation between such calibrated results and the observations. A test case was constructed using the signal measured during CO2 injection (from 2004-2009) in the KB501 well of the In-Salah site, Algeria at only a few tens of spatial measurement points either corresponding to: 1. a “realistic” PS network selected in a highly vegetated region in western France or 2. a series of CR selected through a space-filling criterion. The comparison with the observations over the whole area confirmed that 80% of the temporal observations were fitted by the GOP method over the region defined by the CR network with a density of ~ 1 CR/km2. Comparisons with the calibrated model results and with the direct application of a spatio-temporal kriging confirmed the better performance of GOP as well.