Integrated Seismic Structure, Stratigraphy & Magnetic Basement Interpretation: Offshore Louisiana Shelf

Michael Alexander
Integrated Geophysical Corporation, Houston, TX

This paper presents a rationale for using an integrated interpretation of seismic and magnetic data to reduce risk for a deep play. The methodology has application not only in the Gulf of Mexico (GOM) but also in similar geologic settings.

Basement, defined here as the magnetic top of crystalline crust, may not correspond locally to “acoustic” basement identified in some GOM literature as a mid-Jurassic sequence boundary (MJS). Depth differences between basement and MJS, ranging up to thousands of feet, are significant because they infer the existence of local pre-MJS troughs with large volumes of nonmagnetic formations and deep hydrocarbon-generating “kitchens”.

An example of integrated integration is illustrated on a north-south seismic section from the Louisiana Shelf. It demonstrates a relationship between potential reservoirs, faults for trapping and/or migration pathways, potential “kitchens”, and basement structure.The posted basement and MJS profiles cross a set of basement ridges, troughs, and faults. A strong reflector, generally coincident with the MJS depths, is conformable with the basement surface except over the basement trough. Here the reflector shows north dip and supports interpretation of an anomalously thick pre-MJS section.

Reflections marking the top of Cretaceous-Jurassic (K-J) section are conformable with dips of the underlying basement. Two complex K-J features overlying a basement trough, adjacent basement ridges, and a north-verging basement thrust are deemed attractive targets given their positive structure, proximity to potential deep pre-MJS hydrocarbon “kitchens”, and adjacent faults to provide “plumbing” for favorable hydrocarbon migration.

In contrast, both basement and seismic structure to the south show a regional deep from which early-stage hydrocarbons would have migrated laterally away to more favorable locations.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery