On the use of microtremors for hydrocarbon detection

The link of spectral anomalies of microtremors to underlying hydrocarbon reservoirs is very controversial, as field experiments support both positive and negative opinions, and there is not a solid theory supporting this work hypothesis. We conducted field tests at different sites, with and without oil and gas presence, to add new experimental data to the ongoing studies. Microtremor information may become repeatable (and so physically meaningful) only when the observation duration exceeds a few days, but even in this case, factors such as topography and active faults may severely bias the signal. Ocean waves impinging the coasts provide natural background noise, which stands out clearly when the observation time exceeds a dozen days or so, in such a way that human noise is stacked out statistically over time. Microtremors recorded in (relatively) deep wells may provide useful information about ongoing production in a reservoir, and may link well data and seismic surveys, as their interferometric analysis can provide information comparable to Vertical Seismic Profiles.