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Model-driven inversion of the Fortuna National 3D seismic data in the Macuspana Basin, onshore Mexico

Summary A seismic inversion has been successfully performed on a cube covering the Fortuna National concession in the Macuspana Basin (onshore Tabasco, Mexico) despite rather poor quality of the data. Out of 26 wells, only MAC201 is suitable as input for the inversion. The model-driven inversion scheme requires: the zero-phased seismic block, a seismic wavelet and an acoustic impedance (AI) macromodel. In MAC-201 a density curve has been estimated from the sonic using Gardner's rule. A synthetic trace is compiled and matched to the seismic. A zero-phasing operator has been calculated after applying a bulkshift and the wavelet extracted via cross-correlation techniques. The macro-layer model represents a 3D continuous horizon model. Micro-layers are automatically drawn within these units providing grid cells with constant AI. These values are perturbed and convolved with the wavelet to produce a synthetic trace. The difference with the original seismic trace is determined. A small 3D volume around the target trace is used to ensure stability of the inversion solution. The results are evaluated in AI composite plots, sections and micro-layer maps. Gas in the wells is generally characterised by low AI anomalies within the reservoir layer. The inversion results are in good correspondence with those obtained in a concurrent AVO study. The AI cube allows better definition of the volumetrics and delineation of "sweet spots". It ultimately leads to a more optimal choice of future well locations.