Early Detection of Fault Activation Using Surface Tilt Monitoring During a CO2 Injection Project

Abstract

Tracking the migration of injected CO2 is critical to understanding the performance of subsurface intervals selected for CO2 sequestration. Measuring and analyzing the shape and magnitude of the surface deformation caused by subsurface CO2 injection, provides confidence that sequestered CO2 will remain in the target formations. Surface deformation information for onshore injection operations can be obtained via InSAR satellite imagery or an array of high-resolution tiltmeters installed in shallow (10-15m deep) boreholes.In this study, synthetic tilt data produced from a full 3D finite element model of the In Salah CO2 injection site, are used to determine the shape and location of the CO2 plume at the three injection wells. A strong tilt signal ( > 0.1 microrad) can be observed well ahead of the equivalent detectable surface heave ( > 2 mm, typical InSAR limitation magnitude). The inverse analysis for an array of ten tiltmeters around each of three injection wells clearly shows whether the injected CO2 remained in the target layer or leaked into a nearby fault. Results show that tracking the tilt vectors on the top of the fault can inform the operators of the onset of the fault pressurization.