Petroleum Systems of Deep-Water Basins - Gulf Coast Section SEPM

Exploration in Deep Water Basins…Where Next?
Dan M. Worrall
Shell International Exploration and Production, Inc.
200 North Dairy Ashford
Houston Texas 77079 USA
e-mail: dmworrall@shell.com
Michael W. Bourque
David R. Steele
Shell Deep Water Services, Houston, Texas USA
Abstract
Exploration success in the first two decades of deep water exploration has been highly focused on a particular
basin type: Atlantic rift margin basins draped by thick deep water clastic strata, deposited downdip of large Tertiary
drainage systems and above a mobile substrate of shale or salt. Most are downdip extensions of working petroleum
systems on the adjacent shelf and onshore. Reasons for the preponderance of discovery volume to date in this basin
type include: 1) a very high density of structural and stratigraphic/structural leads and prospects; 2) the ready availability
of high quality reservoir in deep water channels and fans; and, 3) focused maturation of oil-prone source rocks
caused by the Tertiary depocenters. The source rocks are varied and have been found in synrift, post-rift and deltaic
settings. Trap types have included channels over deep-seated salt-or-shale structural highs, flanks and faulted flanks
of salt or shale minibasins, and submarine fans draped over underlying structural highs. Exploration in plays in the
upper slope portions of some of these basins is beginning to show signs of maturing, as new play development continues
to move outboard and deeper. In the latter part of the last decade exploration plays have been made in the distalmost
structured portions of some of these basins.
Where then might the next prolific frontier basins and/or plays in the deep water theatre be found? Many ideas
that are being pursued in our industry, or are still on the drawing boards, include:
1. Moving still farther downdip of these focus basins into the largely unstructured basin floor fans that lie on the toe
of slope and abyssal plain. Although analogs exist for successful traps in this setting given at least low angle structural
inclination, clear difficulties include the occurrence of thermal maturity and the inferred low density of traps.
2. Moving deeper within these focus basins, especially to non-amplitude supported and/or subsalt objectives.
3. Moving laterally from the mobile substrate basins into less structured provinces nearby, that still have sufficient
sedimentary section to provide reservoir and mature source rocks.
4. Exploring other, similar mobile substrate basins.
5. Exploring basins with other structural origins, for example transform margins, or fold and thrust belts in active
margin settings.
6. Exploring non-turbidite (e.g., carbonate) reservoirs in deep water settings.
These and other more novel play concepts will be required to continue the rapid growth seen in the past two
decades of the deep water play.
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