25th International Meeting on Organic Geochemistry IMOG 2011

P-285
Understanding Fluid Inclusion Stratigraphy (FIS) Data
Daniel Stoddart 1 , Paul Farrimond 2
1 Lundin Norway AS, Oslo, Norway, 2 Integrated Geochemical <strong>International</strong> (IGI) Ltd, Bideford, United
Kingdom (corresponding author:daniel.stoddart@lundin-norway.no)
Fluid Inclusion Stratigraphy (FIS) involves the
analysis by mass spectrometry of volatile components
present in rock samples, performed on each sampled
cuttings interval and core chips throughout a well.
We applied Principal Components Analysis (PCA)
to FIS data from wells in the Barents Sea with the aim
of better understanding the data and the interrelationships
between the different ions to define
source rock vs. hydrocarbon-bearing intervals, marine
vs. terrestrially deposited organic matter, and an oil
characterization scheme. An attempt has been made
to integrate well log, bulk and molecular geochemical
data with FIS data to refine interpretations.
FIS data were available for 23 wells in the Barents
Sea. 15 wells were selected for individual analysis by
PCA. Several PCA approaches were tested, using
different selections of FIS data (all ions, selected ions,
ratios & parameters) and different data pre-treatments
(normalisation and autoscaling [standardisation]);
optimal results were obtained using a suite of 166 ion
abundances (14 ions being excluded due to their
frequent absence or apparent unreliability) which
were normalised and autoscaled prior to PCA.
Example data from 7220/6-1 well, a commercially
dry hole with good oil shows and residual
hydrocarbons in carbonates. PC1 scores data are
coincident with a sharp increase in methane and
paraffin FIS responses in the carbonates. The PC1
loadings plot indicates that PC1 is dominated by
heavier hydrocarbon ions, thus producing a
―hydrocarbon log‖. A ratio of (as logs) 111+113 AMU
to 29 AMU gives a ―C8/C2 log‖ which interestingly
shows a more consistent oil signature throughout the
carbonates, but falling towards its base. This may
indicate that ratios (i.e. compositional information) are
more reliable than raw ion abundances, the latter
being influenced by too many other factors (e.g.
inclusion abundance).
High acetic acid concentrations are evident
directly below a zone of high methane and paraffin
values. Gas chromatograms from in/around the high
acetic acid zones show water washing/biodegradation
effects lending credence to the idea that this may
represent a paleo-OWC.
Source rocks and coaly intervals produce similar
FIS spectra to oil-bearing intervals, and respond
similarly in PCA. Hekkingen Fm. samples often show
a good relationship between PCA response and total
organic carbon content, suggesting that kerogen
content may control the FIS signal in these intervals.
Parameters including aromatic ions or methane (15
AMU) intensity are useful in distinguishing between
FIS responses from marine source rocks and coaly
intervals.
This study will show how FIS data can be more
fully explored.
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