Wasiu O. Raji
Theoretical rock physics modelling and synthetic time lapse seismic data are used to explore the use of attenuation to indicate saturation in hydrocarbon reservoirs. Given the time variant changes in saturation and the properties of the reservoir rock, the patchy saturation mechanism and the theory of modulus-frequency-dispersion are applied to formulate a theoretical curve that describes the dynamic effect of saturation on seismic attenuation. Attenuation is measured in time lapse synthetic seismic records and the theoretical curve is used to estimate the approximate saturation that gave rise to the Seismogram-derived Attenuation (SdA). Results show that SdA can be used to indicate the changes in reservoir saturation if a relationship between SdA and saturation is known. The saturation values predicted by the theoretical model are consistent with the saturation values inverted from SdA. This study also shows that seismic attenuation depends on porosity, mineral content of the rock, and the property of the saturating fluid(s). For the case study, at a saturation of 0.7, a 10% reduction in porosity caused a 5.9% rise in attenuation; and a 10% reduction in the bulk modulus of the saturating fluids caused an 11% reduction in attenuation
