Ground surface monitoring for CO

Tracking the migration of injected CO2 is critical to understanding the performance of subsurface intervals selected for CO2 sequestration. Subsurface CO2 injection may cause a deformation at the surface of the earth. Measuring and analysing the shape and magnitude of this surface deformation provides confidence that sequestered CO2 will remain in the target formations and can alert operators to the existence of hidden faults or fractures which may necessitate redesign of the injection schedule or remediation of the geological hazards. Surface deformation information for onshore injection operations can be obtained via Interferometric Synthetic Aperture Radar (InSAR) satellite imagery or an array of high-precision tiltmeters installed in 10–15 m deep boreholes. However, in the case of offshore injection operations, InSAR data is not available. Due to the lack of tilt data at In Salah field at Krechba, Algeria, synthetic tilt data has been produced using a 3D forward model. The synthetic tilt time-series data at ten locations around each injection well has been used in inverse analysis. Results show that the shape and direction of the CO2 plume in the subsurface can be accurately determined through inverse analysis of the tilt time-series data.