Comments on “Determination of strength parameters and quality assessment of Denizli travertines (SW Turkey)” Ibrahim Cobanoglu and Sefer Beran Celik, 129–130 (2012) 38–47

Persistent scatterers synthetic aperture radar interferometry (PSI) analysis is viewed as a promising monitoring technique for multiyear detection of ground surface displacements during long term CO2 injection into deep aquifers (of the order of 25 to 50 years). echnique was successfully utilized at the CO2 storage site of In-Salah (Algeria). Nevertheless, this success may not be generalized to future onshore industrial-scale CO2 storage sites, which are planned in far more complex contexts mostly presenting natural terrains, either agricultural or vegetated areas, i.e. characterized by poor PS density, which might locally drop to zero, hence hampering the deployment of the PSI technique. The objective of the present paper is to discuss the constraints on the PSI application regarding the specificities (magnitude, spatial or temporal scales and evolution) of the deformation phenomenon associated with the CO2 injection into storage aquifers. This discussion is supported by the estimates of the expected spatio-temporal evolution of surface vertical displacements caused by CO2 injection in deep aquifers by combining the approximate solutions for pressure build-up and for the associated vertical displacements in an elastic half-space. A possible option to enhance the performance of the PSI technique is explored, namely the deployment of a network of corner reflectors CR corresponding to artificial devices installed on ground to complement the existing “natural” PS network. A methodology is then proposed to optimize the CR network (number and position) in an iterative strategy (e.g., every 10 years) relying on the prediction of surface deformation. The methodology is illustrated by a CO2 injection scenario in the Paris basin context.