Fluid Discrimination Using De-Trended Seismic Impedance

Date

2021-05

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Abstract

Compaction effects can obscure the impedance separation between hydrocarbon-bearing and fully brine-saturated sandstones. Discrimination can be improved by removing depth-related trends from inverted seismic impedance. Although the ratio of compressional-to-shear wave velocity versus seismic compressional-wave impedance cross plots show differences between pay, brine sand, and shale trends, using absolute inverted impedances only imperfectly distinguishes hydrocarbon sands from brine sands due to outliers. In a given locality, statistical comparison of well log and seismic-derived impedances enables a shale impedance model to be obtained and used as a lithology baseline to de-trend the impedance from the effects of burial and overburden. This has the effect of unmasking anomalies associated with hydrocarbon-bearing sands and serves as a reliable fluid discriminator. For an offshore Gulf of Mexico dataset on the flank of a salt dome, with pay occurring over a wide range of depths, we find that hydrocarbon-bearing sands are identified with a greater success rate after de-trending the absolute seismic impedance.

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Keywords

Impedance, Fluid, Salt Dome

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