Analysis of low frequency passive seismic data from an experiment over a carbonate reservoir in Abu Dhabi

Passive seismic experiments using a small array of 3-component instruments were conducted over an onshore carbonate oilfield in Abu Dhabi. The aim is to confirm and understand the origins of a low frequency signals (2.5-2.8 Hz) that has been observed above several hydrocarbon reservoirs in the area and considered as a hydrocarbon indicator. The results of the experiments indicate that a narrow-band of low frequency signal is present above the hydrocarbon reservoir as previously claimed, but that this signal is also observed over nearby assumed non-reservoir locations. Variations in the character of the signals recorded 12 hours apart during midday and midnight periods were observed. The possible causes of this low frequency energy are not well understood. However, using the array of 3-components instruments, we are able to determine the apparent velocities and the azimuth of the wave fronts as well as the particle motion of the recorded low frequency waves. The results indicate that the observed signals are most likely due to some type of surface waves with the azimuth to the source pointing towards the nearest coastline in the area (the Arabian Gulf).