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Abstract
In-situ combustion (ISC) is a successful method with great potential for the
production of heavy oil. Application of ISC is limited, however, because the
process is complex and not well understood. A significant open question for ISC
is the formation of coke or “fuel” in correct quantities that is sufficiently
reactive such that combustion is sustained. We study ISC from a laboratory
perspective in one-meter long combustion tubes that allow monitoring of the
progress of the combustion
front using X-ray computed tomography (CT). Two crude oils with API gravities
of 12 and 9 are studied. Images of oil movement and banking in situ are
obtained through appropriate analysis of the spatially and temporally varying
CT numbers.
Combustion tube runs are quenched prior to front breakthrough at the production
end thereby permitting a post mortem analysis of combustion products and in
particular of the fuel (coke and coke-like residues) just downstream of the
combustion front. Fuel is analyzed using both scanning electron microscopy
(SEM) and X-ray photoelectron spectroscopy (XPS). XPS and SEM results are
useful to identify the shape, texture, and elemental composition of fuel in the
X-ray CT images. The SEM and XPS results aid in differentiation among
combustion tube results with significant and negligible amounts of clay
minerals. Initial results indicate that clays increase the surface area of fuel
deposits formed and this aids combustion. Additionally, comparisons are made of
coke-like residues formed during experiments under an inert nitrogen atmosphere
and coke-like residues from in-situ combustion. Study results contribute to an
improved mechanistic understanding of ISC, fuel formation, and the role of
mineral substrates in aiding or impeding combustion. CT imaging permits
inference of the width and movement of the fuel zone in situ.
Introduction
In-situ combustion (ISC) offers many potential advantages over other thermal
recovery processes, including greater recovery of the original oil in place,
lower production and capital costs, minimal usage of natural gas and fresh
water, a partially upgraded crude-oil product, reduced diluent requirements for
transportation if upgrading is sufficient, and significantly lower greenhouse
gas emissions (Castanier and Brigham, 2003). In-situ combustion is a
multiphysics, reactive-transport process with vigorous production of heat,
carbon oxides, and steam resulting from the oxidation of a small fraction of
the hydrocarbons in place. A key to well-functioning ISC is the creation of
fuel that is subsequently oxidized if the flux of air is sufficient. The fuel
is composed of coke and coke-like residues resulting from heating of the
oil.
The ISC recovery process was initially field-tested in 1934 (Sheinman et al.,
1973) and air injection projects date to the early 1900’s (Prats, 1986) Since
then, combustion recovery methods have been implemented in a variety of
geological and geographical settings. To date, hundreds of projects around the
world have been started (Karimi and Samini, 2010, Dingley, 1965). Notable field
projects are Suplacu de Barcau in Romania, Balol and Santhal in India, Bellevue
in Louisiana, USA, and Morgan in Lloydminster, Alberta, Canada (Mitra et al.,
2010, Turta et al., 2005, Kuuskraa et al., 1983, and Marjerrison and Fassihi,
1994). The ISC process also has potential to operate in reservoirs that are
greater in pressure, lower in quality, thinner and deeper, onshore and
offshore, and contain significant shale (Kleindienst, 2005).
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