Evolving Thoughts on the Origins of Oil in the Gulf of Mexico Basin and Its Impact on Oil Quality

Industry’s understanding of the origins of oil has changed as a result of both a growing understanding of foundational science and access to data. For thirty years there have been numerous advances in the understanding of processes and concepts associated with the formation and alteration of petroleum accumulations. There has also been in the Gulf of Mexico access to a geochemical data suite based on a large number of samples from piston cores, with some oil and gases, and lesser amounts of actual source rocks. Together these data and the background science have moved industry away from the concept of source-reservoir couplet to establishing the presence of a number of stratigraphically discrete source rock intervals within the Gulf of Mexico basin ranging in age from Jurassic through the Eocene and their areal distribution. This work has also established the importance of vertical migration and crude oil alteration. The lithology and depositional setting of these stratigraphic units has resulted in oils of different characters, including variable API gravity values and sulfur contents. For the most part these different petroleum systems are geographically defined. Many of these oils have been altered, often reducing oil quality. There are, however, some processes, such as mixing and cracking that may actually improve oil quality. Oil quality is of increasing economic importance as exploration shifts to deeper water and as reservoirs become more challenging as a result of the quality of the oil’s ’s impact on producibility and price.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California