Geomechanical modelling of ground surface deformation induced by CO2 injection at In Salah, Algeria: Three wells, three responses

Abstract

This study investigates the ground surface deformation above three injection wells throughout CO2 injection between mid-2004 to early-2011 in the In Salah CO2 storage project at Krechba, Algeria. A coupled three-dimensional finite element model of three wells (KB501, KB502, and KB503) was developed. The model accounts for the CO2 diffusion in the reservoir and structural features including permeable fractures and faults, as well as the poroelastic deformation of the reservoir and overburden layers which result in the ground surface deformations during CO2 injection. The character of the ground surface deformation above each injection well was different, suggesting a different CO2 plume shape in the subsurface. An ellipse-shaped heave above KB501 indicates that the CO2 plume shape followed the anisotropic permeability in the reservoir, KB502’s double-lobe surface heave pattern is associated with the activation and pressurization of a vertical fault and finally, the elongated surface uplift pattern above KB503 is linked to the presence of permeable fractured zone in vicinity of the well, as indicated by seismic surveys. The two distinctive structural features in the vicinity of KB502 and KB503 were included in the numerical model, accounting for a hydraulically conductive fault in the caprock and a fractured zone in the reservoir, respectively. The observed surface deformation was utilised to tune the orthotropic mechanical properties of the fault and the fractured zones. The simulation results are in good agreement with the measured InSAR data. In addition, assigning anisotropic permeability to the reservoir plays a significant role in successfully simulating surface uplift patterns.