--> ABSTRACT: Seismic Depth Conversion Problems Associated with the Mississippi Canyon in the Vicinity of Ewing Bank Block 305 Field, Offshore Louisiana, by Gregory P. Leveille, Surinder K. Sahai, Phillip G. McDaniel; #91003 (1990).

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ABSTRACT: Seismic Depth Conversion Problems Associated with the Mississippi Canyon in the Vicinity of Ewing Bank Block 305 Field, Offshore Louisiana

Gregory P. Leveille, Surinder K. Sahai, Phillip G. McDaniel

Ewing Bank Block 305 field is located on the outermost edge of the continental shelf, approximately 145 km south of New Orleans, Louisiana. The geology of the field is fairly typical of other fields found offshore of Louisiana, except there is a huge, partly filled, Pleistocene submarine canyon that overlies the field. This canyon, which is commonly referred to as the Mississippi Canyon, causes a large seismic depth conversion problem that makes it virtually impossible to correctly map the structure of the field using normally processed marine seismic data.

The Mississippi Canyon is a large erosional feature that was formed at the mouth of the ancestral Mississippi River during the last glacial sea level lowstand. In the vicinity of the field, the canyon is about 10 km wide and 1 km deep, which is approximately two-thirds the size of the Grand Canyon of the Colorado River, and is filled mostly with Holocene sediments. Because the sediments that fill the canyon are very young, their interval velocities are much lower than the interval velocities of the sediments that form the canyon walls. This creates abrupt near surface lateral velocity variations that distort the geometry of seismic reflectors such that the time geometries seen on seismic lines are not at all indicative of the structure of the subsurface.

Using a model-based processing technique and available well control, we have been able to solve this difficult depth conversion problem and have gained a better understanding of the geology of this field.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990