Imaging a thin reservoir by active and passive seismic

The estimate precision of time origin and hypocenter obtained by the shrinking grid method allows using micro-earthquakes as additional illumination sources for seismic tomography. Their contribution is relevant for thin reservoirs, where picking both top and bottom is impossible. What is not visible as a reflection effect, it becomes so as a transmission effect. Surface active surveys provide an extended areal illumination, but the vertical precision of unconstrained reflection tomography may be not sufficient for a thin reservoir. Calibration by well logs or VSP s is needed to match active surface and passive well data properly. The synthetic case presented here is a feasibility study for a real experiment, where micro-seismicity may be induced by CO2 injection into an aquifer under a producing hydrocarbon reservoir. The injection is aimed at reducing the environmental impact of CO2, but it can benefit hydrocarbon production too, by improving the reservoir characterization.