Characterisation of the Krechba CO2 storage site: critical elements controlling injection performance

The In Salah CO2 storage project in Algeria, initiated in 2004, provides a unique early-mover case study on CO2 storage. After 5 years of operation, the project has developed a substantial storage-unit characterisation and monitoring dataset. The question we address in this paper is: which reservoir features have proven most critical in controlling the injection performance so far? This is also an important question for future CO2 storage sites, as part of the planned global ramp-up in CCS as a greenhouse gas mitigation option.

Our main findings are that structural geological and rock mechanical aspects are most critical in the early injection phase, while characterisation of the pore space, combined with the dynamically created fracture permeability, becomes more important when considering the medium to long-term effects (10–1000 years) including geochemical, fluid dynamical and geomechanical aspects. When considering the quantity and type of data that are needed to sufficiently characterise this CO2 storage site, high quality 3D seismic proves to be highly valuable (despite its relatively high cost). For the pore space characterisation, core samples from both the reservoir and the caprock are vital in order to calibrate and properly interpret static and dynamic well data.

Finally, monitoring datasets, including well-head gas and tracer data, time-lapse seismic data, and satellite (InSAR) monitoring data need to be interpreted and only bring true value when utilised with detailed geological descriptions and models of the subsurface.