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New computer techniques recently developed in our laboratory and applied to the correlation of oil families have for the first time been applied to the correlation of oils and source rocks from the Alaskan North Slope. The computer process utilizes the entire information content of gas chromatograph-mass spectrometric (GC-MS) analyses of whole oils and rock extracts in the correlation process. Previous correlation efforts utilizing GC-MS data have been limited to the use of preselected biomarkers or have required laborious and time-consuming procedures to find new biomarkers.
The reproducibility of common sample preparation procedures including extraction procedures (Soxhlet, shakeout, and sonication) and fractionation by liquid chromatography (alumina and silica gel) were evaluated at the beginning of this study. This evaluation involved the use of stable-labeled deuterated 2- to 5-ring aromatic hydrocarbon spikes. The spikes were added to the oils or sediments prior to extraction and/or liquid chromatography. The results of these studies indicated that liquid chromatographic fractionation is not sufficiently reproducible for our correlation technique and an exhaustive extraction procedure is required to recover indigenous organic matter from sediments. Whole crudes and sediment extracts prepared using a Soxhlet extraction procedure were, therefore, used or the correlations. Sediment extracts were screened by gas chromatograph-flame ionization detector prior to GC-MS analysis to insure adequate extractable organics for correlation purposes. GC-MS data were collected under very carefully controlled conditions to minimize instrumental variability. Oil-oil and oil-rock correlations were then made using the computerized correlation process. The oils were grouped into two families whose members were shown to have undergone different degrees of alteration.
Seven of the 15 sediment samples provided contained sufficient extractable organic matter to warrant correlation of the GC-MS data, but only 3 of these sediments have vitrinite reflectance maturities within the oil generation window. Correlation of the oils provided (excluding the Seabee condensate) with these 7 sediments showed no unique correlations. Several marginal correlations exist where a sediment correlates equally well with several oils, but these oils do not belong to the same group (or family). This may mean that each group has mixed sources, that we have not yet sampled the source rocks, and/or that he algorithm used needs further development to perform oil-rock correlations.
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