Chapter 2
Hydrocarbon Systems Analysis of the Northern Gulf of Mexico: Delineation of Hydrocarbon Migration Pathways Using Seeps and Seismic Imaging

Kenneth C. Hood
Exxon Exploration Company
Houston, Texas, U.S.A.
Current address: ExxonMobil Exploration Company, Houston, Texas, U.S.A.

L. M. Wenger
Exxon Exploration Company
Houston, Texas, U.S.A.
Current address: ExxonMobil Upstream Research Company, Houston, Texas, U.S.A.

O. P. Gross
Exxon Exploration Company
Houston, Texas, U.S.A.
Current address: Esso Production Malaysia Inc., Kuala Lumpur, Malaysia

S. C. Harrison
Exxon Exploration Company
Houston, Texas, U.S.A.
Current address: Consultant, Houston, Texas, U.S.A.

ABSTRACT

Widespread oil and gas seepage in the offshore U.S. Gulf of Mexico has allowed the extension of hydrocarbon systems and maturity maps far beyond well control. Analysis of sea-bottom dropcores and imaging of sea-surface slicks have complemented Exxon's integrated, multidisciplinary study of sources, maturation, and migration pathways. Our approach involved development of a regional geologic framework through interpretation of 2-D and 3-D seismic data, identification and mapping of potential source intervals, and delineation of likely migration pathways to reservoirs and seismic-amplitude anomalies. Hydrocarbon compositions from more than 2000 reservoired oils, 600 reservoired natural gases, and 3000 hydrocarbon-bearing, sea-bottom dropcores help constrain such source-rock characteristics as organic-matter type, depositional facies, level of maturation and, to some extent, age. East of the Mississippi River Delta, the complete stratigraphic section is visible on seismic sections, and wells have penetrated deep source intervals. To the west, correlative organic-rich rocks have been sampled onshore and from sheaths overlying salt diapirs offshore. Integration of these data into a regional geologic framework provides a strong basis for hydrocarbon-systems interpretations.