Fingerprinting and Correlation Investigation of Selected Crude Oils from Kuwait Using Results of Compound Specific Isotope Analysis of Biomarkers
Alimi, Hossein *1; Al Khamiss, Awatif 2; Andriyany, Rita 2
(1) Geochemical Services Group, Weatherford Laboratories, Shenandoah, TX. (2) Kuwait Oil Company, Ahmadi, Kuwait.
CSIA, also known as isotope ratio monitoring-GCMS (IRM-GCMS), is a new technique which adds a whole new dimension to oil-oil and oil-source rock correlations. In conjunction with high-resolution biomarker analyses including age-diagnostic GC-MS-MS analyses, CSIAB provides the most in-depth and most source- specific analysis currently possible for correctly identifying in detail and understanding the petroleum systems in a basin.
A total of 14 crude oils from Tertiary (C1-C5) and Cretaceous (C1-C9) reservoirs in Kuwait have been analyzed using a suite of geochemical methods, including CSIA of alkanes and biomarkers (CSIA/A and CSIA/B) to investigate their source relationship.
Except for oil samples T4, T5, C1 and C7 which are more enriched in paraffinic compounds, other Tertiary and Cretaceous oils analyzed are enriched in aromatic compounds with saturate and polar compounds components present in subordinate quantities.
Comparing the oils based on their bulk isotopic compositions the following sub-grouping may be recognized:
- Subgroup A, consists of oils T5, C7, C8, and C9
- Subgroup B, consists of Tertiary oils T1, T2, and T3
- Subgroup C, consists of Tertiary oil T4 and Cretaceous C1-C6 which show isotopic compositions falling within the subgroups A and B.
Compound specific isotope analysis of alkanes (CSIA/A) was difficult for the Tertiary oil samples because they were biodegraded and their n-alkane concentrations were very weak. This accounts for the high variability of the measurements and unevenness of the trend lines. Results of compound specific isotope analysis of biomarkers failed to distinguish any samples in Tertiary samples. The numbers for both the hopanes and steranes are isotopically relatively light on the whole, which is typical for an anoxic depositional environment of deposition for the source rock
Compound specific isotope analyses (CSIA) were performed on only seven Cretaceous oils (C1-C7). The CSIA-B isotope curves (Figure 2) show relatively consistent patterns, except for those of oil samples C1 and C2. The Cretaceous oil C1 shows the most radical differences suggesting it may be from an entirely different source or source facies compared to the other Cretaceous oils analyzed in this study.
The Cretaceous oils investigated in this study show relatively flat n-alkane isotope curves that do not differentiate them further into distinct families.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain