Influence of Salt Geometry and Salt-Sediment Interaction on Seismic Imaging

Bui, Huyen ¹; Jamieson, George ¹; Snyder, Fred ¹; Herbert, Sharlene ¹; Becker, David ¹; Smith, Martiris ¹
(1)WesternGeco, Shlumberger, Houston, TX.

The dynamic mechanism of salt system and salt tectonics is mainly driven by the weight of overburden and subsalt strata. Regional extension also plays an important role in rising salt diapirs or in their subsidence. When the salt moves, it rolls-over and carries the sediments along with it. We have observed many inclusions inside the salt with different patterns on many seismic sections in the Gulf of Mexico. These inclusions cause changes of velocity inside the salt body. These lithology changes inside the salt have also been observed in many outcrops onshore US and also in many wells penetrating through the salt in the Gulf of Mexico. Therefore, the constant velocity that has been traditionally used in the salt for seismic depth imaging is no longer valid.

Salt and sediments have intimate interaction with each other. In the other words, the sedimentation can drive the salt flows. The formation and deformation history of the salt plays very important roles in the spatial distribution of the lithological facies, and in the generation, and migration of hydrocarbons. Understanding the salt shape and salt-sediment interaction are not just required for structural geology. It will help with the determining the correct velocity of the salt for a better anisotropic velocity model in seismic imaging. We will describe a project where we have incorporated the geological knowledge to re-interpret the salt shape and to update the base of the salt by non-seismic methods (EM and gravity). Then, we have re-migrated the seismic data with the new salt shape in an area in the Green Canyon, in the Gulf of Mexico with very good results. Hence, incorporation of geological understanding and geophysical methods for more accurate salt shape interpretation will significantly help to improve the subsalt images for “true earth model”.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.