Geochemical characterisation of crude oils from offshore of Sarawak and Sabah
A total of six crude oil samples from Baram and Bokor oilfields at Baram offshore of Miri, Bayan and D35 oilfields at Balingian offshore of Bintulu, Samarang oilfield at offshore of Labuan and South Furious oilfield at offshore of Sabah were studied for their organic geochemical characteristics....
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| Format: | Thesis |
| Language: | English |
| Published: |
2013
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| Subjects: | |
| Online Access: | http://ir.unimas.my/id/eprint/9388/2/Zainah%28fulltext%29.pdf |
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| Summary: | A total of six crude oil samples from Baram and Bokor oilfields at Baram offshore of Miri,
Bayan and D35 oilfields at Balingian offshore of Bintulu, Samarang oilfield at offshore of
Labuan and South Furious oilfield at offshore of Sabah were studied for their organic
geochemical characteristics. The crude oils were fractionated on silica gel column
chromatography into aliphatic hydrocarbons, aromatic hydrocarbons and polar compounds.
The fractions were analysed by gas chromatography-flame ionization detector (GC-FID) and
gas chromatography-mass spectrometer (GC-MS). Ratio of biomarkers such as
pristane/phytane, pristane/C17, phytane/C18, carbon preference index (CPI), ΣC21-C31/ΣC15-
C20, oleanane/C30hopane, %C27/(C27-C29)steranes, %C28/(C27-C29)steranes, %C29/(C20-
C29)steranes and (20S/(C20S+C20R)steranes were used as source correlation indices of crude
oil. The presence of 18α (H)-oleanane is an evidence that all crude oils sourced from
terrigenous higher plants. Gammacerane detected at trace amount in the Baram, Bokor,
Samarang and South Furious crude oils indicating input of marine organic matter under saline
environments. The D35 and Bayan crude oils were deposited under oxic conditions of peat
swamp environment with high terrestrial organic input. Baram and Bokor crude oils are
related to fluviomarine environment, while Samarang crude oil is related to coastal swamp
environment. South Furious crude oil was deposited under aquatic depositional environments.
Derivatised F3 and F4 fractions have been successfully silylated with tert-butyldimethylsilyl
(TBDMS) as shown by the appearance of several additional peaks in the chromatogram of
derivatised samples compared to underivatised samples. The varied organic composition of the F3 and F4 fractions showed the crude oils consist of different organic compositions from
each other. The fatty acid, ester, aldehyde and ketone groups showed dominance in South
Furious crude oil, while nitrogen containing compound and alcohol groups are dominant in
Samarang crude oil compared to other crude oils. The FTIR results showed functional groups
peaks such as aromatic C-H out of plane and sulfoxide (C2S=O). The similar absorption bands
for all spectra of all the crude oils indicated similarity in terms of group compositions. The
scanning electron microscope (SEM) analysis for asphaltene in all crude oils showed different
structural morphology for crude oils studied. The inductive coupled plasma-optical emission
spectrometry (ICP-OES) analysis on crude oils revealed the highest concentration of Fe and
Zn in Baram crude oil followed by the Bokor, D35, Samarang, Bayan and South Furious
crude oils. Highest concentration of Ni and Ba was recorded in the D35 crude oil, while the
highest concentration of Cr was detected in South Furious crude oil. The cluster analysis
formed three groups, that are group 1 consists of Samarang and South Furious crude oils,
group 2 consists of Baram and Bokor crude oils and group 3 consists of D35 and Bayan
crude oils. Furthermore, principal component analysis (PCA) suggests that Baram, Bokor and
Bayan crude oils are closely related, whereas D35, Samarang and South Furious crude oils are
closely related to each other. |
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