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Salt Emplacement and Displacement History: Sheds Light on Seal Integrity, Case History from the Gulf of Mexico

Selim Sanad Shaker
Geopressure Analysis Services (G.A.S.), Houston, TX

In the Tertiary-Quaternary salt basins of the Gulf of Mexico, compartmentalization is the primary factor in setting up traps capable of retaining hydrocarbons. Geopressured compartmentalization is created by the stresses resulting from interaction between sediment load and salt tectonics. Examination of salt emplacement and displacement history as they relate to the surrounding sediments may shed light on the sealing integrity of potential traps.

This paper presents a case study that compares a disappointing prospect to a field, both located on the south rim of the Auger Basin, a highly prolific area in the deepwater of offshore Louisiana.

The Mt. Massive prospect (Garden Banks Block 600) is structurally higher than, shares the same stratigraphic column with, and is separated from Macaroni Field (Garden Banks Block 602) by a trough. Prior to testing the Mt. Massive prospect, it was compared to Macaroni Field and deemed low-risk. Once drilled, however, results of Garden Banks 600 #1 well were disappointing, as most of the target objectives supported by Seismic Amplitudes were revealed to be wet sands. The well was plugged and abandoned.

A post-drilling assessment of the geopressure profile and sealing capacity show that Macaroni Field is in a different pressure regime than Mt. Massive. A ridge of salt was contemporaneously emerging during sedimentation at Macaroni. On the other hand, the salt wall bounding Mt. Massive prospect had pierced beds post sedimentation. This offers an explanation for the presence of effective seals at the Macaroni Field and, conversely, the breached seals at Mt. Massive.