Contribution to the Discrimination of Field-specific Seismic Amplitude Attenuation Causes

The quantitative use of the seismic amplitude information during the interpretation is a key point for many prospect evaluations and almost all reservoir characterization studies. The local amplitude information of interest is always affected by a series of signal attenuators along the propagation of the incident and reflected wavefield which are highly dependent upon the geological context, structural shape, lithologies and fluids. These many causes of attenuation are often pragmatically treated by a combination of a few well-known tools: spherical divergence compensation, surface-consistent or volumic time & frequency-dependent compensations. Cases where severe amplitude attenuation effects cannot be treated using usual approaches are a serious issue, in particular for seismic characterization of reservoirs. In this paper, a methodology adapted to the study of the impact and relevance of specific attenuation processes is presented; Alternative mechanisms and tools for a quantitative assessment of these processes are proposed. This methodology is illustrated through a field case study, using vertical incidence VSP and 3D surface data. The seismic amplitude attenuation analysis uses the VSP data to validate the modeling of measurable effects and to propose possible causes for the remaining strong attenuation, such as diffuse gas.