Continuous active-source seismic monitoring of C O2 injection in a brine aquifer

Continuous crosswell seismic monitoring of a small-scale [Formula: see text] injection was accomplished with the development of a novel tubing-deployed piezoelectric borehole source. This piezotube source was deployed on the [Formula: see text] injection tubing, near the top of the saline aquifer reservoir at [Formula: see text] depth, and allowed acquisition of crosswell recordings at [Formula: see text] intervals during the multiday injection. The change in traveltime recorded at various depths in a nearby observation well allowed hour-by-hour monitoring of the growing [Formula: see text] plume via the induced seismic velocity change. Traveltime changes of [Formula: see text] (up to 8%) were observed, with no change seen at control sensors placed above the reservoir. The traveltime measurements indicate that the [Formula: see text] plume reached the top of the reservoir sand before reaching the observation well, where regular fluid sampling was occuring during the injection, thus providing information about the in situ buoyancy of [Formula: see text].