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Abstract
Chapter from: M
66: Hydrocarbon Migration And Its Near-Surface Expression
Edited By
Dietmar Schumacher and Michael A. AbramsAuthors:
Tony Barwise, Steve Hay and Jane Thrasher Geochemistry, Generation, Migration
Published 1996 as
part of Memoir 66
Copyright © 1996 The American Association of Petroleum
Geologists. All Rights Reserved. |
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Barwise,
T., S. Hay, and J. Thrasher, 1996, Contamination of shallow cores: a common
problem, in D. Schumacher and M. A. Abrams, eds., Hydrocarbon migration
and its near-surface expression: AAPG Memoir 66, p. 359-362. |
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Chapter
27
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Contamination
of Shallow Cores:
A Common Problem |
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Tony Barwise
BP Exploration
BP Research and Engineering
Centre,
Sunbury on Thames, U.K.
Steve Hay
BP-Statoil R+D Alliance
Trondheim, Norway
Present address:
BP Exploration Company
(Europe) Ltd.
Dyce, Aberdeen, Scotland
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Jane Thrasher
BP Exploration
BP Research and Engineering
Centre
Sunbury on Thames, U.K.
Present address:
Sir Alexander Gibb &
Partners
Reading, U.K.
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Abstract
Detecting migrated
petroleum in shallow cores requires techniques that reliably indicate the
presence of thermogenic petroleum in a core extract. Often, the level of
petroleum in the extract is very low, and in our experience, many surveys
have been prone to some form of contamination. It is important to be able
to recognize these contaminants to avoid ascribing contaminants to actual
petroleum in the core.
The most common form of contamination
in our coring surveys has been distilled vacuum pump oil in the extracts.
This arises during the freeze-drying process when the wet cores are subjected
to a high vacuum to dry them prior to extraction. In many of our shallow-coring
studies, this material was mistakenly interpreted as "condensate" largely
because of its fluorescence characteristics. However, GC-MS analysis shows
that this material is of low thermal maturity and has a similar composition
in coring studies from widely differing parts of the world where very different
source characteristics are expected. This constancy in composition is strongly
suggestive of contamination. Despite attempts to remove this pump oil with
a series of filters in the freeze-drying apparatus, it has proved to be
difficult to prevent it from reaching the cores. We now air-dry all our
cores to prevent this contamination and have found that our data more clearly
show the presence of true petroleum in cores. Several other contaminants
have been detected during coring surveys, mainly from contamination in
the laboratory. It has proved necessary to carefully monitor each coring
survey and the data produced by contractors to achieve reliable interpretations. |
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