AAPG Southwest Section

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Midland Basin Spraberry Exploration using High Resolution Elastic Inversion


Bandwidth extension and seismic inversion have aided in the exploration for and development of Spraberry sands in the Permian Basin. In this study, we investigate the prospectivity and connectivity of a submarine fan system covering an area of 145 sq. km. in the Midland Basin. The sandstone reservoirs are divided into five genetic sequences of Permian age; upper Spraberry, Middle Spraberry, lower Spraberry, Jo-Mill and Dean. They are highly compacted and tightly cemented, low porosity, and have an average recovery efficiency of only 15 percent. Hydrocarbons are trapped by up-dip pinch outs and facies changes at depths of 6,800 to 7,100 feet. Detecting or mapping the lateral continuity of the channel sands is difficult because they are below seismic resolution in conventional seismic data. Sparse-layer reflectivity inversion was applied to the original 3D pre-stack data increasing the 7-50 Hz bandwidth of the input seismic data to 7-100 Hz through the inversion process. The results were validated using well log data. Rock physics analysis of the well logs suggests that clean porous reservoir intervals exhibit abnormally low impedance and compressional-to-shear-wave velocity ratio if the layer can be resolved. Simultaneous elastic inversion run on bandwidth extended prestack gathers revealed impedance and velocity-ratio anomalies in structurally advantageous positions that were later verified by drilling as being productive reservoirs. Overall, the new dataset improved detectability and resolution that contributed to greater understanding of the lateral connectivity of lower Spraberry channel sands, and enabled geobody extraction for reservoir static modelling.