Abstract

Borehole measurements of salt-body P-wave interval velocities from 55 wells in the vicinity of the Keathley Canyon and Walker Ridge areas of the Gulf of Mexico vary from 13,966  ft/s (4256  m/s) to 18,535  ft/s (5649  m/s) with mean velocity of 14,920  ft/s (4547  m/s) and standard deviation of 726  ft/s (221  m/s). The velocities vary significantly with latitude. Five different interval velocity zones have been identified with each having specific associated mineralogies within a latitude range. In the midlatitude zones, sylvite, various clastics, and small traces of anhydrite and gypsum are found within the salt, yielding a salt interval velocity variation from 14,388 to 14,965  ft/s (43864544  m/s). The salt interval velocity in the southern limits of the study area is higher than 15,000  ft/s (4572  m/s) and is associated with more gypsum. The northernmost wells are anhydrite rich and exhibit the highest velocities. The interval velocities are relatively uncorrelated and are insensitive to factors such as wellbore temperature, depth, and overburden pressure. Composite medium modeling of mixed salt-body mineralogies and multiple regression analysis indicate that compositional variation within the salt body can explain the observed velocity variations.

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