Fuel Formation During In-Situ Combustion of Heavy Oil
- Berna Hascakir (Stanford University) | Cynthia Marie Ross (Stanford University) | Louis Marie Castanier (Stanford University) | Anthony Robert Kovscek (Stanford University)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.4.6 Thermal Methods, 4.1.9 Heavy Oil Upgrading, 5.4.2 Gas Injection Methods, 2.4.3 Sand/Solids Control, 6.5.1 Air Emissions, 4.3.4 Scale, 5.4 Enhanced Recovery, 5.3.4 Integration of geomechanics in models, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.2.1 Phase Behavior and PVT Measurements, 5.5.2 Core Analysis, 4.6 Natural Gas
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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.
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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