In Salah CO2 Storage Project

In Salah CCS in central Algeria is one of the world’s earliest large-scale industrial carbon capture and geological storage (CCS) projects and served as a major technical learning case for onshore CO₂ sequestration monitoring and reservoir behavior. The project was developed as a joint venture between Sonatrach, BP, and Equinor (formerly Statoil) and was integrated into the In Salah gas production operation, which produces natural gas from tight sandstone reservoirs containing significant CO₂ concentrations. Rather than venting separated CO₂ during gas processing, the project compressed and reinjected the CO₂ into a deep saline formation (the Carboniferous Krechba reservoir) at approximately 1.8–2.0 km depth. Between 2004 and 2011, roughly 3.8–4 million tonnes of CO₂ were injected via several horizontal injection wells located at the Krechba field. The storage interval consisted of relatively low-permeability sandstone overlain by thick sealing caprock, and injection created a distinctive plume geometry that became a key research focus for understanding pressure buildup and geomechanical response. A defining aspect of In Salah was its extensive monitoring, measurement, and verification (MMV) program, which used advanced techniques including satellite-based InSAR (interferometric synthetic aperture radar) to detect millimeter-scale surface deformation caused by subsurface pressure changes, time-lapse seismic surveys, microseismic monitoring, and downhole pressure and temperature measurements. These datasets demonstrated that CO₂ injection can cause measurable ground uplift linked to reservoir pressurization and fracture propagation, providing unprecedented insights into the coupling between injection strategy and geomechanics. Around 2011, injection was halted after analysis suggested that pressure buildup and fracture behavior in the caprock required reassessment of long-term risk management; however, the stored CO₂ remained contained, and the project yielded significant operational and scientific lessons regarding plume migration, fracture dynamics, and monitoring strategies for onshore CCS in tight formations. From a strategic perspective, In Salah helped establish best practices for early CCS deployment, particularly in integrating capture with upstream gas processing, demonstrating horizontal injection well design, and pioneering remote sensing as a monitoring tool. Although it did not continue as a long-term commercial storage operation, its extensive public datasets and technical studies influenced later CCS projects globally by highlighting the importance of reservoir characterization, pressure management, and adaptive monitoring frameworks.