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

Abstract

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 (>0.1μRad) 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. 1. INTRODUCTION Geological storage of carbon dioxide in the deep subsurface was identified as one of the key technologies for reducing the emission of greenhouse gases to the atmosphere and mitigating global warming and climate change (Baines & Worden, 2004; Hepple & Benson, 2005; Schrag, 2007). The types of geological reservoirs suitable for large-scale, long-term subsurface storage of CO2 mainly include deep saline aquifers, existing oil and gas fields, and deep unmineable coal seams. There are major concerns on the large-scale injection of CO2 into these geological formations and the long-term storage security such as injection induced reservoir stress and deformation, CO2 plume migration and leakage, well integrity, caprock sealing performance, potential fault reactivation and notable seismic events (Rutqvist et al., 2015). Effective modelling and monitoring of geological CO2 injection and storage are therefore essential to better understanding of the mechanisms of the storage process, to the development of reliable geological carbon storage technologies and their successful implementation (Adriana Paluszny et al., 2020; Saeed Salimzadeh et al., 2018).