Seismic inversion products are routinely used for earth modeling and influence the drilling program. However, this process is not trivial as the deepest target intervals are at around 12,000ft and the drilling windows are very narrow, in the range of 20-40ft. We demonstrate that spending a large effort in the processing of the seismic data before inversion produces much better end results. In the Delaware Basin, large areas of modern 3D seismic data are available for seismic inversion. Based on wireline logs and core data, the Leonard Shale is known to correlate with density. By integrating inverted seismic and well data, we can predict PHIE (effective porosity) and TOC (total organic carbon) and map quality and distribution of the Leonard Shale in our development areas. The seismic processing included a special refraction statics solution that reduced the static error in this difficult area to a minimum. Noise attenuation was done in a cascading manner to avoid damaging the amplitudes. A 5D interpolation was performed to produce a regular sampled dataset and fill in acquisition holes. Vertical transverse isotropy (VTI) was corrected and horizontal transverse isotropy (HTI) was investigated but the effect was not large enough to influence the flatness of the gather events and therefore no HTI correction was done. After the full azimuthal pre-stack time migration, the CDP gathers went through additional noise cancellation and multiple attenuation processes before angle stacks were generated. The data were zero phased using log data from 16 wells. Simultaneous inversion was run by joint impedance and facies inversion. The software system is designed to extract facies and petrophysical properties from pre-stack seismic data. This methodology yields improved spatial resolution of facies and properties within a specific target. By cross-plotting well-derived acoustic impedance at seismic frequency with the inverted rock properties, we see an average correlation coefficient of 0.76. Wells with a full set of conditioned sonic and density logs demonstrate improved correlation coefficients over the average set. A previous attempt at inverting the seismic to rock properties failed as the original processing was not sufficient to obtain these high quality results.

 

Image source: Marianne Rauch-Davies and Steven W. Smith (2017) Detailed Oriented Seismic Processing Leads to More Accurate Elastic Attribute Results in the Delaware Basin. Unconventional Resources Technology Conference, Austin, Texas, 24-26 July 2017: pp. 2614-2620.

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