Great Geologists | 131
There is little doubt that the concepts of sequence stratigraphy
have revolutionized both sedimentary geology and petroleum
geology over the last forty years. Sequence stratigraphy
examines the stratigraphic geometries and associated patterns
of sedimentary facies that are generated by relative sea-level
change. In doing so, it is a valuable tool for predicting the
occurrence of, for example, reservoir and source rock facies
and understanding the architecture of reservoirs. Of equal
importance, it provides a catalyst for the integration of seismic
and well and outcrop data in addition to detailed sedimentological,
biostratigraphical and geochemical studies. Put simply, many of
the deep-water plays being explored for today are lowstand fans,
predicted from sequence stratigraphic principles and identified on
high-resolution seismic data.
The sequence stratigraphic methodology first came to
prominence with the publication of seminal papers by Peter Vail
and his colleagues from Exxon in 1977. Since then, sequence
stratigraphic studies have become commonplace and the
science has developed its own particular jargon to account for
the countless ways in which sediments respond to sea-level
change. But Vail and his colleagues did not just bring sequence
stratigraphy to the petroleum geologists’ tool box; they reactivated
an old idea that some sea-level changes are synchronous and
global in nature. Such changes are termed eustatic, as first
introduced by the great Austrian geologist Eduard Suess in 1888.
This has tremendous predictive value, although the recognition of
eustasy in the rock record has both ardent supporters and critical
skeptics.
Peter Vail – Photograph courtesy of Northwestern University.
Peter Vail
Peter Vail was born in 1930 in New York. After attending
Dartmouth College, New Hampshire he earned his Master of
Science and PhD degrees at Northwestern University, Illinois.
Following this in 1956 he joined the Carter Oil Company in Tulsa,
Oklahoma. This company was an affiliate of Exxon, with whom he
would spend much of his career, until retirement in 1986 when he
joined the faculty at Rice University in Houston.
With an academic background in stratigraphic mapping, and
influenced by two of the great professors at Northwestern
University, Larry Sloss and Walter Krumbein, his initial tasks at
Carter Oil were subsurface mapping and correlation projects for
exploration in the Paradox Basin, Illinois Basin and Venezuela.
This led him to consider what were the right units to map and the
importance of time in stratigraphy. In his view, log correlations
needed to be placed in time context, not simply be lithological.
Correlation of facies changes and maps of geological time slices
could be more valuable than maps of lithostratigraphy. This was
the beginning of a strong association with biostratigraphers who
could provide the important age calibration and constraint.