Global Sensitivity Analysis for Supporting History Matching of Geomechanical Reservoir Models Using Satellite InSAR Data: A Case Study at the CO2 Storage Site of In Salah, Algeria

Abstract Injection of CO 2 into deep aquifers may cause surface heave of several millimeters per year. This was revealed by the interferometry analysis of satellite images from the descending orbit (ASAR-sensor of ENVISAT mission) over the period 2003–09 during CO 2 injection at KB-501 well of In Salah (Algeria). These data are of great interest for getting a better insight into the characterization of both the host reservoir and overburden rock materials via a history-matching exercise using geomechanical numerical simulations. Yet, this analysis is hindered by the large number of unknown model parameters. In the case of In Salah, the calibration should handle 10 parameters including the elastic parameters of four rock formations and the initial stress state. To reduce this number, we adopted a variance-based global sensitivity analysis to evaluate the contribution of each parameter to the differences between observations and numerical results over the injection period at each spatial location. Since running the geomechanical reservoir model was time consuming (several hours), we relied on a response surface–based approach (here of type kriging) to compute the Sobol' sensitivity indices using a limited number of long-running geomechanical simulations (here 100). On this basis, we brought two evidences. First, the dominant influence of the reservoir's stiffness on the observed surface displacements was highlighted. Second, the heterogeneous nature of the spatial distribution of this property was studied.