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GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 234-26
Presentation Time: 9:00 AM-6:30 PM

RESIDENCE OF RHENIUM AND OSMIUM (RE-OS) WITHIN ASPHALTENE AND MALTENE SUB-FRACTIONS OF A HEAVY CRUDE OIL


DIMARZIO, Jenna M.1, GEORGIEV, Svetoslav V.1, STEIN, Holly J.2 and HANNAH, Judith L.2, (1)AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523, (2)Centre for Earth Evolution and Dynamics, University of Oslo, P.O. Box 1072 Blindern, Oslo, 0316, Norway; AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523, dimarzioj@outlook.com

Little is known about the placement of Re and Os in crude oil molecules or fractions. The isotopic consequences of oil maturation and migration, including possible resetting of the geochronometer, are also unclear. This information is paramount to the use of the Re-Os geochronometer in oils to constrain oil generation and migration histories.

In this study, heavy crude oil was separated into asphaltenes and maltenes. Two asphaltene aliquots were separated into sub-fractions using heptane-dichloromethane/methanol (DCMM) and acetone-toluene mixtures in specific proportions. Bulk maltenes were separated via open column chromatography into saturates, aromatics, and resins. Re-Os concentrations and Os isotopic compositions of chemically separated sub-fractions were determined by HPA digestion and ID-NTIMS analysis.

The third, intermediate solubility heptane-DCMM sub-fraction has the highest Re (1495 ppb) and Os (2.5 ppb) concentrations. In contrast, the first, least soluble acetone-toluene sub-fraction has the highest Re (1291 ppb) and Os (1.9 ppb) concentrations. 187Re/188Os ratios of heptane-DCMM sub-fractions increase from the first to the sixth sub-fraction, while 187Os/188Os ratios are highest in the intermediate sub-fractions. Acetone-toluene sub-fractions show an overall decrease in 187Os/188Os ratios with increasing sub-fraction solubility, whereas 187Re/188Os ratios remain fairly constant. Maltene separation shows that resins have the highest Re and Os concentrations and 187Os/188Os ratios, with 187Re/188Os ratios slightly lower than the aromatics. Saturates contain very little Re and Os.

Our work suggests Re and Os may preferentially bind with specific organic molecules within oil: each sub-fraction is, to a degree, chemically distinct, and their Re-Os contents and isotopic compositions differ. Our observations support the premise that oils consist of different components with distinct Re-Os isotopic systematics, although it is unclear when and how this Re-Os fractionation occurs in the petroleum system. ICP-MS analysis of asphaltene and maltene sub-fractions (work in progress) may reveal important trace metal correlations to help us better understand the residency of Re and Os in oils.

Session No. 234--Booth# 31

T14. Geologic Energy Research (Posters)
Tuesday, 27 September 2016: 9:00 AM-6:30 PM
Exhibit Hall E/F (Colorado Convention Center)
Geological Society of America Abstracts with Programs. Vol. 48, No. 7
doi: 10.1130/abs/2016AM-281621
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