We analyse microseismic data from a pilot installation in the commercial sized CO2 injection project at Krechba, Algeria. Over 5000 microseismic events were detected from August 2009 to June 2011 using a master event waveform cross-correlation method. Most events can be directly related to the injection at well KB502. The period with the highest microseismic activity correlates with a period where the maximum applied pressure has most probably exceeded the minimum principal stress in the injection interval. Using S-P wave traveltime differences and event azimuth we can separate various distinct event clusters. Although an accurate event location is not possible due to the limited receiver network, the events most probably come from the injection reservoir interval. Moment magnitudes of the events have been determined and range between MW -1 and MW 0 with a few larger magnitude events up to MW 1. Differences in b-value between event clusters may give some insight about different types of fracturing and may be related to the in-situ stress regime.


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