Carbon Isotope Analysis: A New Tool for Monitoring and Interpreting the In-Situ Combustion Process
- Richard J. Hallam (BP Resources Canada Ltd.) | R. Gordon Moore (U. of Calgary) | H.R. Krouse (U. of Calgary) | Douglas W. Bennion (U. of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- November 1990
- Document Type
- Journal Paper
- 517 - 523
- 1990. Society of Petroleum Engineers
- 4.3.3 Aspaltenes, 4.1.2 Separation and Treating, 5.4 Enhanced Recovery, 5.1.1 Exploration, Development, Structural Geology, 4.6 Natural Gas, 2.4.3 Sand/Solids Control, 1.6.9 Coring, Fishing, 5.4.6 Thermal Methods, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.2 Reservoir Fluid Dynamics, 4.1.5 Processing Equipment, 2.2.2 Perforating, 5.3.2 Multiphase Flow
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This paper investigates the use of carbon isotope analysis for monitoring and interpreting responses from the in-situ combustion process. The major finding was that the type of reaction occurring at the combustion front can be distinguished by carbon isotope analyses. These reactions include the classic burning profile at the leading edge; super-wet or low-temperature combustion; a wide combustion zone with a secondary front, which is indicative of oxygen channeling; and carbonate decomposition in carbonate core material. This tool is valuable because, at times, making these interpretations without temperature data or from gas analyses alone is not possible. The study also demonstrated the feasibility of using carbon isotope data to track communication among injection and production wells.
Carbon isotope analysis has been used for a number of years in petroleum exploration and in the monitoring of carbonate decomposition during thermal recovery projects. Garon et al discussed the use of carbon isotope analysis for monitoring combustion-tube tests, and Cathles et al reported its application in monitoring a field steamflood project. The objectives of this study were to determine whether carbon isotope data could be used to determine the nature of reactions occurring during the in-situ combustion process and to identify wells in combustion communication. Data were collected from 20 combustion-tube runs conducted at the U. of Calgary. All but one of these runs used oils from deposits in Alberta and Saskatchewan, Canada. Field results also were collected from a wet-air/wet-oxygen combustion pilot in the Cold Lake oil-sands deposit and a wet-air combustion project in the Wabasca deposit, both in Alberta.
Carbon has two stable isotopes, 12C and 13C, with approximate average abundances of 98.89 and 1.11%, respectively. The abundance of each isotope in a sample is measured by mass spectrometry, and the reading is expressed as a ratio. The accepted unit of isotopic measurement is the value, given in per mil or parts per thousand with the symbol /oo, The 13C value in /oo is defined as
The international standard is called PDB because it is based on a belemnite sample taken from the Peedee formation of South Carolina. When a sample is enriched in the 13C isotope, then it has a more-positive (less-negative) 6 value and is called "heavy." Conversely, when a sample is depleted of the 13C isotope, it has a more-negative value and is called "light". In this study, the gases were separated with a gas chromatograph with a 1.84-m [6.0 ft], 0.63 m [0.25-in.] OD glass column, packed with Poropak Q. The column was indirectly cooled with liquid air down to 20C [40F] After sample introduction, the temperature was increased at 50C [9019 per minute up to 180C [356F]. Methane was eluted in just under 2 minutes, whereas the CO2 peek appeared 8 minutes later. Higher hydrocarbons up to pentane are well separated and can be collected for analysis. Each eluted gas was routed through individual furnace tubes containing CuO at 800C [1,472F]. The water and CO2 of combustion were collected in a glass coil trap cooled in liquid air. Helium carrier gas was then pumped from the frozen sample. The liquid air bath was replaced by dry-ice alcohol to retain the water-while the CO2 was transferred to a calibrated volume for yield measurement with a capacitance manometer. The CO2 was then analyzed with a stable isotope mass spectrometer constructed with Micromass 903 components for carbon isotope analysis. Gas sample size for the mass spectrometer ranged upward from less than 1 mL, or about 1 mg carbon equivalent. To place the costs of the analysis in perspective, the gas chromatograph used for this study cost about $20,000, a state-of-the-art computer-controlled mass spectrometer may exceed $150,000, and a crude mass spectrometer capable of conducting the analyses for a combustion project might cost $30,000.
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