"Deepwater Reservoir Systems; learning from analogs from the Northern Gulf of Mexico". (Abstract)
Prof William Galloway, AAPG Distingushed Lecture
Department of Geological Sciences, The University of Texas at Austin
Abstract
The Cenozoic sedimentary fill of the northern Gulf of Mexico (GOM) basin contains
thick, reservoir-rich successions deposited in both constructional and destructional
slope systems. Slope and base-of-slope sand bodies are principal objectives of
deep-burial, sub-salt, and deep-water plays that dominate recent GOM exploration.
Turbidite channel fill, lobe, and sheet deposits constitute the reservoir facies within
both kinds of systems.
Constructional slopes were dominated by deposition of allochthonous sediment and
include delta-fed and shelf-fed slope apron and submarine fan systems. Regional offlap architecture characterizes constructional slopes. Syndepositional deformation
of salt and shale substrates created dynamic and complex slope morphologies. Both
salt evacuation and fault displacement formed intraslope basins that filled with
stacked, uplapping successions of slope facies. Repeated "fill and spill" episodes
characterize these intraslope basins.
Destructional slope systems record local to subregional shelf margin and upper slope retreat with consequent development of a significant bounding surface
(composite slide plane, canyon-cut surface, or regional mass-wasting surface).
Recycled autochthonous upper slope sediment forms a lower slope debris apron. Though of secondary volumetric importance in the GOM, destructional slopes create
highly productive reservoir systems in autochthonous apron, submarine canyon fill,
and megaslide deposits. Further, large submarine fan systems commonly originate at sites of slope destruction.
The Pliocene Globoquadrina altispira (PGa) genetic sequence contains productive examples of both constructional and destructional slope reservoir associations. The
sequence records a 2± my period of relatively slow sediment supply. In the northeast
Gulf, more than 200 km of the paleo-shelf edge retreated as much as 20 km from its
early Pliocene location. Here, a thin slope apron contains multiple sand-rich belts that
traverse several intraslope basins. Slope erosion and bypass initiated deposition of
an elongate submarine fan system on the basin floor.
In contrast, the west-central Gulf PGa shelf margin prograded up to 30 km as a broad
delta-fed slope apron following collapse of a shelf edge megaslide. Distinctive exploration plays are created by slope sand facies contained within each of these
slope system types.
Biography
Education
1966 Texas A&M University, B.S. Geology
1968 The University of Texas at Austin, M.A., Geology
1971 The University of Texas at Austin, Ph.D., Geology
Experience
Present: Morgan Davis Centennial Chair in Petroleum Geology, Department of
Geological Sciences and Senior Research Scientist, Institute for
Geophysics. The University of Texas at Austin.
1975-1983: Research Scientist and Senior Research Scientist, Bureau of Economic
Geology, The University of Texas at Austin
1994-1995: Visiting Professor, National Centre for Petroleum Geology and
Geophysics, University of Adelaide, Australia
1990: Nordic Visiting Professor in Petroleum Geology, The University of
Bergen, Norway
1981: Klabzuba Visiting Professor of Geology and Geophysics, University of
Oklahoma, Norman, Oklahoma
1970-1975: Research Scientist and Director, Geologic Section, Exploration
Research Division, Continental Oil Company, Ponca City, Oklahoma
Research Interests
Terrigeneous clastic depositional systems.
Sequence stratigraphy.
Petroleum geology.
Sedimentary
uranium deposits.
Memberships
American Association of Petroleum Geologists
Fellow, Geological Society of London
American Geological Institute
SEPM - Society for Sedimentary Geology
Publications
Author of more than 100 papers and abstracts on subjects ranging from clastic sedimentology, sequence stratigraphy, petroleum geology and resource evaluation, hydrogeology, and uranium geology. Co-author of the popular reference "Terrigenous Clastic Depositional Systems", first published In 1983, with a second edition In 1996.
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