Microseismic monitoring and interpretation of injection data from the In Salah CO2 storage site (Krechba), Algeria

Abstract

Microseismic data analysis together with interpretation of injection data at the In Salah CO2 storage site provides a valuable tool for improved understanding of the subsurface injection and storage processes. More than 1500 microseismic events have been detected semi-automatically between August 2009 and May 2012 and the occurrence of the events correlates clearly with increased injection rates and well-head pressures. Most likely the fracture pressure has been exceeded temporarily, resulting in a sudden increase of microseismicity. Waveform cross- correlation of the events demonstrates that most events occur in three distinct clusters. Clusters with shorter S-P wave differential travel times clearly correlate with the CO2 injection at KB502, whereas events with larger S-P wave times do not. An uncertainty analysis and a network design study conclude that a more extensive microseismic network would be needed to resolve locations and potential correlations with injection data.