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New insights from a 3D earth model, deepwater Gulf of Mexico

Integrated Geophysics Corporation, Houston, Texas, U.S.

Glenn Morton

Kerr-McGee Corporatin, Aberdeen, Scotland, U.K.

Corresponding author: info@igcworld.com

The first 20% of the full text of this article appears below.

A 3D earth model, a geophysical/geologic three-dimensional (3D) model of the earth, is best described in terms of its exploration objective. This means that when its geologic target is established, the model is designed to represent the geologic environment surrounding the prospective target. The areal extent covered can range from regional (i.e., hundreds of OCS blocks) to a detailed nine blocks.

At minimum, the earth model is an accumulation of the results of multiple sciences approximating the earth's lithology. At best, through the skilled interpretation of integrating the results of these sciences, it can bring new insight through the refinement of the salt configuration.

The 3D earth model described in this article encompasses 144 square miles—16 OCS blocks in the deepwater region of the Gulf of Mexico. The primary objective—i.e., to establish a quantitative interpretation of the structural configuration of the base of an allochthonous salt mass as shown on Figure 1—was achieved through the following steps:

• Assess the velocity field in the project area and interpret a calibrated clastic sediment velocity model suitable for the generation of the pseudo-density conversion for density/depth surfaces used in the 3D earth-modeling scheme.
  
• Build a 3D earth model based on detailed full tensor gradient and regional marine gravity data constrained by bathymetry, density/depth surfaces derived from the calibrated clastic sediment velocity model, a seismically interpreted top of salt horizon, the magnetic basement structure surface, and the Mohorovicic discontinuity surface.
  

View larger version (138K): [in this window] [in a new window]   Figure 1. Seismic section illustrates the problem of determining the base of an allochthonous salt mass. The deeper reflectors show the possibility of the sedimentary section under the salt, but how far laterally and at what depth does it truncate against the salt are questionable (Seismic section courtesy of Veritas).