Seismic wave attenuation: Promising attribute for fluids, fractures and tar mats characterization in Abu Dhabi oilfields

Seismic wave attenuation can be used to enhance geophysical interpretation in the reservoir zones, this has great benefit for oil and gas industry. Getting accurate attenuation profiles is prominent to get correct geophysical interpretation, however this is not an easy task since the methodology is not enough mature yet. The difficulty is higher for complex media like those composed carbonate rocks, such media are known to be highly heterogeneous. The subsurface of Abu Dhabi region is known to be mainly composed of carbonate rocks. We developed a new method to estimate the intrinsic attenuation and scattering separately, from downgoing waves of VSP data. This new method is based on seismic interferometry technique and it is less sensitive to upgoing waves compared to classical methods. We estimated attenuation from sonic waveforms by using new method well adapted for such type of data, this method was successfully applied in previous studies. We got accurate and high-resolution scattering and intrinsic attenuation profiles from five wells belonging to five oilfields located in Abu Dhabi region. Compared to previous studies carried out in siliciclastic media, the attenuation shows high variation over the depth, and the scattering shows significant contribution on the total attenuation. We explain this by the high heterogeneity characteristic of carbonate rocks. We found very interesting correlation between the attenuation profiles and the other petrophysical logs, such as the sonic and oil saturation logs. The scattering shows a good correlation with the fractures, and intrinsic attenuation shows a good sensitivity to the fluid existence. So the combination between the scattering and the intrinsic attenuation is a promising and can be very useful for the petroleum exploration, especially in the case of Abu Dhabi reservoirs known to be highly fractured.