In situ combustion (ISC) process has drawn more
and more attention in the development of heavy oil reservoirs as a
result of its high recovery efficiency. Although numerous studies
have been reported that oil properties exhibit significant changes
during the combustion process, the reaction mechanisms and evolution
of oil components are still not well understood. In this work, the
compounds of produced oils collected from a three-dimensional simulated
production model (container) at different duration times after combustion
being initiated and the original oil were characterized at the molecular
level using gas chromatography (GC), gas chromatography–mass
spectrometry (GC–MS), and high-field Fourier transform ion
cyclotron resonance mass spectrometry (FT-ICR MS). Both aromatic and
acidic components were analyzed. The aromatic components showed relatively
more stable characteristics than those of acidic components, and no
obvious changes in aromatic compound distributions were observed by
the positive ion atmospheric pressure photoionization (APPI) FT-ICR
MS analysis. Small aliphatic acids were detected in the ISC oils, which were responsible
for the high total acid numbers (TANs). The acidic O
x
(x = 1–3) compounds, which have major
contributions to the increase in TAN, were generated in greater abundances
compared to that of the original crude oil. The carbon number distributions
of the O1 and O2 classes in the produced oils
significantly shifted to a lower carbon number region, with the dominant
distribution from 15–40 at the initial state to 10–30
at the longest duration time. The double bond equivalent (DBE) values
decreased during the combustion process. The generated acidic O1 components with DBE values less than 4 were also found in
negative ion electrospray ionization (ESI) analysis, indicating the
oxidation of hydrocarbons to alcohols.
This work examines a type of rapid pore-filling event in multiphase flow through permeable media that is better known as Haines Jump. While existing microfluidic experiments on Haines Jump mostly seek to maintain quasi-steady states through very low bulk flow rates over long periods of time, this work explores the combined use of a highly structured microscale transport network, high-speed fluorescent microscopy, displacement front segmentation algorithms, and a tracking algorithm to build evolution graphs that track displacement fronts as they evolve through high-speed video recording. The resulting evolution graph allows the segmentation of a high-speed recording in both space and time, potentially facilitating topology-cognitive computation on the transport network. Occurrences of Haines Jump are identified in the microfluidic displacement experiments and their significance in bulk flow rates is qualitatively analyzed. The bulk flow rate has little effect on the significance of Haines Jump during merging and splitting, but large bulk flow rates may obscure small bursts at the narrowest part of the throat.
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