Scientific Strategy to Explain Observed Spectral Anomalies over Hydrocarbon Reservoirs Generated by Microtremors

Worldwide one has observed narrow-band, low-frequency (1.5-4 Hz) tremor signals on the surface over hydrocarbon reservoirs (oil, gas and water multiphase fluid systems in porous media). These ‘hydrocarbon tremors’ possess remarkably similar spectral and signal structure characteristics, pointing to a common source mechanism, even though the depth (some hundreds to several thousands of meters), specific fluid content (oil, gas, gas condensate of different compositions and combinations) and reservoir rock type (such as sandstone, carbonates, etc.) for each of those sites are quite different. However, the physical mechanisms underlying these observations are presently not fully understood. Therefore we propose a scientific strategy for a better understanding of those phenomena. Using well-known rock physical relationships we have identified on macro-, meso- and microscale different mechanism which can induce anomalies in the low-frequency band. Using different numerical approaches we are able to compare these mechanisms with observations in the field.