 Gulf
Coast Region
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Basin Analysis and
Petroleum System Characterization and Modeling, Interior
Salt Basins, Central and Eastern Gulf of Mexico
By Ernie Mancini and Don Goddard, University
of Alabama and Louisiana State University
The University of Alabama and Louisiana
State University have undertaken a cooperative five-year,
two-phase fundamental research project involving sedimentary
basin analysis and petroleum system characterization and
modeling of the North Louisiana Salt Basin and Mississippi
Interior Salt Basin. According to the United States
Geological Survey, the hydrocarbon volume of these basins
ranks them in the top 8% of the most petroliferous basins of
the world. Phase 1 work focused on data compilation,
determination of the tectonic, depositional, burial and
thermal maturation histories, basin modeling and petroleum
system identification for the North Louisiana Salt Basin;
comparison of the geohistory of the North Louisiana Salt
Basin to that of the Mississippi Interior Salt Basin and
assessment of the undiscovered and underdeveloped reservoirs
of the North Louisiana Salt Basin. Phase 2 work focuses on
characterization and modeling of the Upper Jurassic
Smackover petroleum system, characterization and modeling of
other Mesozoic petroleum systems and refinement of the
assessment of the undiscovered and underdeveloped reservoirs
of the North Louisiana Salt Basin.
Three active petroleum source rocks (Oxfordian,
Albian and Cenomanian-Turonian) have been reported from the
onshore north central and northeastern Gulf of Mexico area.
Based on the assessment of potential petroleum source rocks
in the North Louisiana Salt Basin, only the Upper Jurassic (Oxfordian)
Smackover lime mudstone beds were determined to be an
effective regional petroleum source rock in this basin. The
components of the Smackover petroleum system in the North
Louisiana Salt Basin include the following: (1) the
underburden and overburden |
Figure 1. Location map of interior salt
basins and subbasins in the north central and northeastern
Gulf of Mexico area. |
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strata include
pre-rift, syn-rift and postrift deposits, which are a
result of their rift-related geohistory; (2) organic rich
and laminated Smackover lime mudstone beds are the petroleum
source rocks; (3) petroleum reservoir rocks include
Jurassic, Cretaceous and Tertiary siliciclastic and
carbonate strata; (4) petroleum seal rocks are
Jurassic, Cretaceous and Tertiary anhydrite and shale beds;
and (5) structural or combination traps characterize the
basin with movement of the Jurassic Louann Salt also
producing a complex array of structures that serve as
petroleum traps. These structures include peripheral salt
ridges; low relief salt pillows, salt anticlines and turtle
structures; and piercement domes. From burial history and
thermal maturation history profiles for wells in the North
Louisiana Salt Basin, hydrocarbon generation and maturation
trends have been observed.
Initiation of
oil and associated gas was at a vitrinite reflectance (Ro)
level of 0.55% and the commencement of essentially only
thermogenic secondary, non-associated gas generation was at
a Ro level of 1.3%. Cessation of thermogenic gas generation
was at a Ro level of 4.0%. The generation of hydrocarbons
from Smackover lime mudstone beds was initiated at 6,000 to
8,500 feet during the Early Cretaceous and continued into
the Tertiary. Hydrocarbon
expulsion from
Smackover source rocks began during the Early
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Cretaceous and continued into the
Tertiary. Commencement of oil expulsion began first in the
southern (downdip) portion of these basins in the Early
Cretaceous and peaked in the late Early Cretaceous.
Smackover lateral hydrocarbon migration was probably of an
intermediate range (80 km or 50 mi). Hydrocarbon migration
into overlying strata was probably facilitated by vertical
migration along faults.
The Bossier Shale has been identified as a
potential Mesozoic petroleum source rock in the North
Louisiana Salt Basin. Phase 2 work on characterizing these
shale beds using thermal maturation history has been
initiated with completion expected in early 2008.
PTTC workshops transferring Phase I insights to industry
were held in Tuscaloosa, Alabama and Shreveport, Louisiana
in spring 2007. Contact Bennett Bearden, Alabama (email
bbearden@geo.
ua.edu) or Don
Goddard, Louisiana (email
dgodda1@lsu.edu)
for further information about these workshops. There is
other information about the research project and its reports
online (link reports online to
www.netl.doe.gov/
technologies/oil-gas/Petroleum/
projects/EP/Explor_Tech/
15395UofAL.htm). Future workshops on later findings
and insights are anticipated. 
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