25th International Meeting on Organic Geochemistry IMOG 2011

P-338
Examples of the relationship between reservoir character and
hydrocarbon signatures measured at the surface
Paul Harrington, Alan Silliman
W. L. Gore & Associates, Inc., Elkton, MD, United States of America (corresponding
author:asilliman@wlgore.com)
Adsorbent-based surface geochemical samplers are
used to detect a wide range of volatile organic
hydrocarbon compounds in soil. Many of these
compounds are of likely thermogenic origin, from
underlying petroleum reservoirs. Microbuoyancy
theory has been proposed as the mechanism for
vertical migration of organic compounds, through the
stratigraphic column to the surface. Heavy saturated
compounds as heavy as phytane (C20) are
detectable in minute amounts (10 -9 grams).
Geochemical samplers are used to collect surface
geochemical data from exploration areas, and also
from available regional petroleum production and dry
well sites (―control samples‖).
A relationship is noted between reservoir quality, as
measured by the net pay thickness – porosity product,
and strength of surface geochemical signature, as
measured by pattern and mass of hydrocarbon
compounds. A relationship is also noted between
strength of surface signature and current production
volume at numerous well sites. Reservoir pressure is
correlated positively with the strength of surface
geochemical signature.
Examples of the correlation between reservoir
character and surface hydrocarbon signature are
presented from geochemical surveys in the Anadarko
Basin of Oklahoma, Oriente Basin of Ecuador, the
Pietu Siupariai Field of Lithuania, the East Texas Salt
Basin, the Green River Basin of Wyoming, and the
Western Canadian Sedimentary Basin.
Practical applications of this relationship are shown by
results from the Banff B Pool reservoir, where a map
of geochemical signature over the reservoir matches
closely a map of (Øh) product for the Banff Formation.
Another example of the correlation between
production strength and geochemical signature
strength is provided by work over the Woodbine sand
trend in eastern Texas. Interpreted well log crosssections
through the Double A Wells gas field show
sand thickening with consequent increase in surface
geochemical signature quality.
In concept, the measurement of local surface
geochemical signal may be used to reveal bypass pay
sections in existing wells. For exploration regions and
proposed well locations, the strength of geochemical
signature would allow priority assignment and ranking
of sites and prospects. The application may also be
used to define sweet-spots in unconventional
hydrocarbon plays. When properly integrated with
other geological and geophysical information, this
surface geochemical technology can significantly
reduced exploration risk.
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