Conventional vs. high-resolution seismic simultaneous inversion and rock property characterization of the Olmos and Eagle Ford unconventional plays, South Texas



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The scope of this work consists of two main objectives. First, identify and characterize the hydrocarbon potential of the unconventional reservoir intervals of Olmos and Eagle Ford formations in South Texas using simultaneous seismic inversion technique. Second, compare seismic interpretation and simultaneous inversion results of the original vs. high-resolution seismic data. High-resolution seismic data result from the application of the spectral inversion method to the original pre-stack seismic data. This method inverts the frequency spectrum for layer thickness and enables the detection and resolution of thin beds below tuning thickness.
Simultaneous inversion is one of the pre-stack seismic inversion processes in which three lithologic volumes (P-impedance, S-impedance and density) are created simultaneously. The Olmos original seismic data simultaneous inversion performed in this area lacked enough vertical resolution to image thin beds (~ 25-30 ft/ 7.6-9 m) within the Olmos productive zone. This shortcoming is improved with the incorporation of high-resolution seismic data. The P-impedance volume generated on the high-resolution data inversion allowed the identification of low impedance thin beds on the SW region of the study area. According to cumulative production values at the wells, the low P-impedance intervals can be highly correlated to high production values; therefore, low P-impedance zone recognition is very important for productive-prone zone identification. The Eagle Ford analysis is done on the P-impedance volume, and two low impedance intervals are recognized within the productive Lower Eagle Ford. High-resolution seismic data permitted the identification of additional reflectors that were below seismic resolution on the original data. Tuning thickness was improved from 120 ft/ 36.5 m on the original data to less than 60 ft/ 18.3 m on the high-resolution data. High-resolution seismic analysis enabled the interpretation of two additional interfaces within the Olmos productive zone and one additional interface within the Eagle Ford productive zone. On cross-plots, the productive zones were recognized within the Olmos tight sand and Eagle Ford shale due to their low density, low P-impedance, high S-wave velocity, and low incompressibility properties.



Olmos, Eagle Ford Shale, Simultaneous Inversion, Pre-stack seismic data, High-resolution, P-impedance