Matt, Veit¹, Renaud Bouroullec¹, Paul Weimer¹, Todd Lapinski¹, Aaron van den Berg¹ 
(1) University of Colorado, Boulder, CO

ABSTRACT: Maturity History of the Source Rocks Below the Mensa and Thunder Horse Fields, Mississippi Canyon, Northeastern Gulf of Mexico

This study shows the maturity history of the Turonian Type II source rock below the Thunder Horse and Mensa fields, the largest oil and gas fields, respectively, in the northern deep Gulf of Mexico. 
This three-dimensional petroleum systems study is based on a grid of 74x89 one-dimensional simulations. The stratigraphy and lithologies are derived from a three-dimensional seismic data (378 mi2) set tied to exploration wells and biostratigraphy. The source rock parameters and boundary conditions, i.e. basal heat flow, paleo-seafloor temperature, and paleo-bathymetry, are derived from literature. The simulations are designed to investigate the contrasting nature of two the neighboring fields, one producing exclusively gas and the other holding mainly oil. 
Due to early higher sedimentation rates and lack of shallow allochthonous salt around the Mensa fetch area, the Turonian source rock matured significantly earlier than below Thunder Horse. At Mensa the oil window (0.6 %Ro) is reached between 20.60-9.4 Ma, and the thermogenic gas window (1.4 %Ro) is reached between 6.2-0.0 Ma. The source rock region within the Thunder Horse fetch area reached the oil window by 10.75-9.4 Ma, with current maturities of 0.7-1.12 %Ro. If present, about 90 % of the source rock below Mensa has already been transformed into hydrocarbons by 7.45-0.0 Ma, whereas below Thunder Horse, 98-15 % still remains to be converted today. The Thunder Horse closure formed between 13.6-9.4 Ma well before the end of the oil window. Most likely, the Mensa closure (7.7-5.8 Ma) was not in place when the source rock passed though the oil window.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.