--> --> Facies Analysis Using Pre-stack Seismic Inversion in the San Andres Formation

AAPG Southwest Section Annual Convention

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Facies Analysis Using Pre-stack Seismic Inversion in the San Andres Formation

Abstract

The San Andres and Grayburg formations are prolific oil producing, conventional reservoirs in the Permian Basin of West Texas. Historically, these reservoirs were produced on the structurally high Central Basin Platform with little potential for exploitation in the deeper Midland and Delaware Basin. In these areas a porous and permeable reservoir does exist, however the charge is not present. This storage capacity, along with its relatively shallow setting, made this reservoir an obvious choice for produced brine injection. To address injection programs within the San Andres a deeper understanding of the regional and local framework is necessary. For this an integrated petrophysical and geophysical analysis was undertaken. This abstract specifically describes an experimental workflow where a seismic facies model is derived from multidimensional crossplot analysis using 3D rock property volumes calculated from seismic inversion. This workflow was performed on an approximately 97 square mile seismic survey in the Midland Basin. A well with a full petrophysical suite and 300 ft. of core taken from the Upper San Andres was used to identify lithology and create a petrophysical model. After careful seismic gather conditioning and detailed petrophysical analysis a model based seismic inversion combined with an iterative supervised neural network was used to create high resolution rock property volumes. The P- Wave Velocity, Density, Young’s Modulus, and Poisson’s Ratio were then used in two separate cross plots to classify ten facies and then calibrated to core derived lithology. The workflow was successful in identifying lithofacies to the level of detection of the seismic survey. When the petrophysical model was applied to other wells in the area the seismic facies model was consistent throughout the 3D seismic survey area making this a useful tool for field development and stratigraphic interpretation in the Midland Basin area.