On the Inversion of Seismic Amplitudes for Lithology, Fluid and Pressure Analysis

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Reservoir description using seismic data has two major components: inversion of seismic data to extract attributes such as P- and S-wave velocities and bulk densities, and relate those parameters to reservoir properties, such as rock and fluid types, fluid saturation, porosity and pore pressure through fundamentals of rock physics. Implicit in the process are two key as-sumptions: the seismic data quality must be good enough for inversion, and the inversion algorithm must be robust and fast enough to yield reliable and consistent results economically with acceptable non-uniqueness. We have seen much progress in both areas. In seismic acquisition, we have seen considerable advancement that contributed to the quality of the seismic data, especially in the prestack domain. These are: single sensor recording (a large number of channels/offset), accurate and cali-brated source and receivers and their positions, digital group forming, and towing cables at shallow water depths to minimize swell noise. All of these enable us to access surface seismic data with high S/N and fidelity that often rivals the fidelity of the Vertical Seismic Profiles (VSP). Seismic inversion algorithms also reached new heights. The advent of high-speed digital data processors and cluster technology impacted significantly the performance of various inversion algorithms; we are now inverting routinely seismic data in the full offset domain and just not restricting ourselves to the stacked data.