25th International Meeting on Organic Geochemistry IMOG 2011

P-339
Geochemical characterization of asphaltenes and maltenes in
organic solid deposits
Eric Lehne, Kentaro Indo, Fenglou Zou, Jose Zacharia, Kamran Akbarzadeh, John
Ratulowski
Schlumberger DBR Technology Center, Edmonton, Alberta T6N 1M9, Canada (corresponding
author:elehne@slb.com)
Flow assurance is a critical concern in
ultradeepwater subsea developments because of the
long flow distances and the high-temperature, highpressure
regimes. Organic and inorganic deposits are
significant flow assurance issues. Well and pipeline
clogging can lead to economic losses and operational
delays. Asphaltenes are known to deposit in both the
petroleum recovery and topside refining processes.
The asphaltenes are normally in equilibrium under
reservoir conditions. During oil production this
equilibrium can be disrupted by a number of factors
including pressure reductions, introduction of miscible
gases and liquids, mixing with diluents and other oils,
and operations such as acid stimulation.
A high-pressure deposition cell was used in this
study to investigate two different oils from one
petroleum system that show different mass/extent of
deposited solids. Both oils are similar in thermal
maturity and are related to the same organofacies but
trace to different lithofacies sources. The crude oil
related to a carbonaceous lithofacies has much higher
amounts of deposited solids than the oil related to a
shaly facies. We compared the asphaltenes from the
parent oils and from the organic solid deposits using
different pyrolysis techniques, elemental analysis, and
UV-visible spectroscopy. Maltenes extracted from the
solid deposits were compared to the parent oils in
terms of bulk composition and biomarker
characteristics using gas chromatography time-offlight
mass spectrometry.
Oil asphaltenes from both parent crudes are very
similar in chemical structure, as indicated by the
analytical techniques. This supports same
organofacies for the oils. Previous studies have
suggested that asphaltenes extracted from organic
deposits are enriched in oxygenated species and
multiple heteroatom classes compared with their
crude oil counterpart [2]. The results of this study
showed that asphaltenes from the deposition cell
reflect only slightly higher aromatic character than
those extracted from the parent oils. This finding
suggests particles of lower molecular weight are
enriched in deposits, which increase slightly the
aromaticity and thermal stability (Fig. 1), and the
atomic O/C ratio of asphaltenes. However, no findings
based on chemical differences between asphaltenes
explained the differences in the deposits.
The occluded maltenes in deposits, however,
differed significantly from those in related parent oils
and between the carbonaceous and shale-sourced
oils. Generally, the abundance of GC-unresolved
complex molecules (UCM), isoprenoids, and cyclic
saturates is much higher in occluded maltenes than in
related parent oils. Occluded maltenes are more
abundant in the deposition cell deposit from the
carbonaceous oil. These maltenes also show a
greater number of biomarkers and aromatics than
those in the deposition cell deposit from the shalesourced
oil.
The results of this study suggest that extent of
asphaltene deposition in a high-pressure deposition
cell is not controlled by asphaltene properties. The
composition of the parent oil (e.g., maltenes) also
impacts the depositional characteristics.
Fig. 1 Activation energy distribution for n-C7 - asphaltenes
from a parent crude oil and for n-C7 - asphaltenes extracted
from related organic solid deposition control experiments.
References
[1] Akbarzadeh, K., Ratulowski, J., Lindvig, T., Davies, T.,
Huo, Z., Broze, G. (2009) SPE 124956-PP.
[2] Juyal, P., Yen, A.T., Rodgers, R.P., Allenson, S., Wang,
J., Creek, J. (2010) Energy Fuels 24, 2320–2326.
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