Abstract

Identification of the locations where hydrocarbon traps leak is of significant practical importance, especially if the leakage controlled the present-day fluid contacts. We have investigated the fluid contacts of five structural traps offshore Norway that are dry or underfilled, and which have apparently had larger hydrocarbon columns in the past. The main focus of our work was to apply observations of bright amplitudes in overburden rocks in order to identify the most likely positions for vertical leakage, and to compare and contrast these observations from different parts of the Norwegian Continental Shelf.

It was seen that bright amplitudes were present in overburden rocks above likely leakage locations in all of the investigated structures. The bright amplitudes line up along fault planes in some of the traps and, in other cases, are clustered along fault intersections. The leakage-related brights were only noted in parts of the overburden sequences, presumably because most of the overburden rocks did not have sufficient permeability to host the gas quantities that are needed for seismic imaging. We conclude that analyses of overburden brights above likely leakage locations can contribute to improved prediction of hydrocarbon–water contacts in the subsurface.

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