Multi-Azimuth 3D provides robust improvements in Nile Delta seismic imaging

Abstract

Introduction Since gas was first discovered in the Nile Delta in late 60's, most exploration programmes have focussed on shallow Pliocene reservoirs, where gas can clearly be seen as bright events on excellent quality seismic data and where exploration success has been very high. The petroleum geology of the deeper pre-Piocene section is fundamentally no different to that seen in the Pliocene, where potential reservoirs consist of sand prone channel systems originating from the Nile. Why then, have we been deterred from exploring in the deeper section? The problem is two fold:Deeper burial and harder rocks mean that reservoir sands and hydrocarbons will be less visible on our seismic data.Pre-Pliocene seismic quality is highly variable and often very poor. (Figure 1) Poor imaging being the result of wavefield distortion though the Messinian layer, attenuation and the presence of complex multiple diffraction noise. These effects are described in the paper. Can multi-azimuth seismic help improve our pre-Pliocene image? Multi-azimuth and wide-azimuth seismic are not new technologies; they have been with us for many years in the form of land and ocean bottom cable surveys. The literature is rich with examples of how high-fold multi-azimuth data can produce stunning improvements over their single azimuth 3D equivalents (e.g. Arntsen & Thompson, 2002. Gaus & Hegna, 2003. Rogno et. al. 1999.). We know from theory and case histories that multi-azimuth data will give us improved signal to noise, improved multiple attenuation and improved illumination. In the Nile Delta, we see that the Multi-Azimuth seismic method should address our two main problems of uneven illumination and multiple diffraction noise.