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The Determination of Petroleum Compositional Similarity using Multiway Principal Components Analysis (MPCA) of Comprehensive Two-Dimensional Gas Chromatographic Data

Ventura, Gregory T.¹; Hall, Gregory J.³; Nelson, Robert K.²; Frysinger, Glenn S.³; Raghuraman, Bhavani4; Mullins, Oliver C.4; Reddy, Christopher M.²
¹Department of Petroleum Geoscience, GNS Science, Lower Hutt, New Zealand.
²Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA.
³Department of Science, U.S. Coast Guard Academy, New London, CT.
4Schlumberger Doll Research, Cambridge, MA.

The accurate establishment of oil similarity is a longstanding problem in petroleum geochemistry and a necessary component for resolving the architecture of an oil reservoir. Traditional, molecular analytical techniques have depended on the comparison of integrated peak areas of two or more compounds by gas chromatography (GC) mass spectrometry (GC-MS) and flame ionization detection (GC-FID). These traditional ratio techniques are problematic because crude oils are at least three orders of magnitude more complex than what is resolvable by these methods and many oil modifying processes can go undetected due to the selectivity of these comparative approaches. Here we use multiway principal components analysis (MPCA) with comprehensive two-dimensional gas chromatography-flame ionization detection (GC×GC-FID) to determine the molecular similarity of the maltene fractions of 8 different crude oils. MPCA works such that every compound eluting within the same 1st and 2nd dimension retention time is quantitatively compared with what elutes at that same retention times within the maltene fractions of other crude oil samples. Each maltene fraction contains upwards of 3500 MPCA quantified components. For this study, reservoir analysis included crude oil sample pairs that were collected sequentially at a single depth within a single well, collected from multiple depths in the same well, and from different depths and different wells but thought to be from the same reservoir horizon. This crude oil sample set was compared by using three different regions within a GC×GC-FID chromatogram. Specific regions were selected to evaluate the effectiveness of MPCA to resolve compositional changes related to the source of the oil's organofacies and its exposure to biodegradation and/or water washing. Compositional artefacts, such as alkenes and alkadienes, introduced during sampling and processing were also quantitatively evaluated. This marks the first time MPCA of GC×GC data has been applied to a petroleum system. We demonstrate that MPCA resolves subtle multi-molecular differences between oil samples, which provide enhanced insight into the overall molecular similarity of various crude oils. MPCA with GC×GC data is capable of dissevering petrochemical changes associated with reservoir connectivity and physical or biological oil alteration processes as well as being a valuable tool for screening fluid contaminants.


AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012