A Low-frequency Passive Seismic Survey in Libya

Low frequency (~1-6Hz) microtremor signals have been measured at the surface in many locations around the world over hydrocarbon reservoirs (multiphase fluid systems in porous media). These low frequency microtremors are observable as modifications of the frequency domain character of passive seismic records. The anomalies in the data spectra possess remarkably similar characteristics, pointing to a common source mechanism, even though depth, hydrocarbon type and matrix rock vary across the complete geological spectrum. Herein we describe observations from a low frequency passive seismic survey over a shallow reservoir in Libya. Specific conditions of the ambient wave field are discussed in detail. In this data set we observe that the magnitude of the hydrocarbon signal can be proportional to the diurnal variations in the total energy of the seismic background.