Prediction of Deep Bright Spots via Gassmann Fluid Substitution and Seismic Amplitude Interpretation in the Vermilion Area, Northern Gulf of Mexico
The objective of this study is to investigate the deep bright spots observed in the Vermilion area, northern Gulf of Mexico, and assess whether they represent gas sand reservoirs. The study was carried out by Gassmann fluid substitution, seismic amplitude interpretation, and Reuss bound examinations of five study areas in the region. The Davy Jones gas discovery of the McMoRan Company at about 8700 m in South Marsh Island Block 230 (close to the Vermilion area) provided both the motivation and initial reservoir parameters for this study. Tertiary Wilcox sands are the primary reservoir targets of the study. The reservoir conditions of Davy Jones were simulated by coding Gassmann’s equations and Batzle’s relations in Matlab to study fluid effects and bright spot signatures. Based on reservoir response, the study areas were compared by fluid substitution analysis and seismic amplitude interpretation. Examination included reservoir response for brine and gas saturated velocities, reflection coefficients, and elastic parameters. Furthermore, Reuss bound studies of the areas were originated from brine-and gas-saturated P-wave moduli bounds of Davy Jones, and they increased the confidence of the reservoir response associated with each study area. Adjusted pore pressures, formation temperatures, and stiffness parameters were found to play a key role in characterizations of the areas. The study showed that three of the study areas (N1, N2, and N3) have probable gas bright spot responses, whereas two regions (N4 and N5) show amplitude anomalies inconsistent with gas bright spots.