Potential Benefit of CO2 in Oxygen Combustion
- W.R. Shu (Mobil R and D Corp.) | H.S. Lu (Mobil R and D Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1984
- Document Type
- Journal Paper
- 1,137 - 1,138
- 1984. Society of Petroleum Engineers
- 5.4.2 Gas Injection Methods
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in-situ combustion with oxygen instead of air has high potential forrecovering heavy and medium oils. Fig. 1 potential for recovering heavy andmedium oils. Fig. 1 illustrates the oxygen combustion process. Among the manyadvantages is a higher concentration of CO2 ( is greater than 80 %) in the fluegas resulting from the absence of nitrogen. This allows more CO2 dissolution inthe oil that helps swell the oil and reduce its viscosity, thus enhancing oilrecovery. Although oxygen combustion has been investigated in the laboratorybefore, the beneficial effect of CO2 has never been demonstratedexplicitly.
In an attempt to simulate the nitrogen-free environment of oxygen combustionand to study the CO2 effect, we conducted a novel combustion tube run in whicha CO2/O2 gas mixture was used in place of air. For comparison, a parallel testwas performed that involved use of air at the same operating conditions.
The laboratory apparatus and the experimental procedure have been describedpreviously. A 13.4API [0.9765-g/cm3] California heavy oil and sands from thesame reservoir were used. The oil has a viscosity of 6,600 cp [6.66 Pa s] at75F [23.9C] and an atomic H/C ratio of 1.52. The pack properties and operatingconditions are listed in Table 1. Both runs were made in the dry combustionmode with about 21 % oxygen in the injection gas. Operations of both tests weresmooth and ignition with the CO2/O2 mixture was successful.
Stabilized combustion was achieved between 2 and 7 hours after ignition forboth runs. The burning characteristics averaged over this time period aresummarized in Table 1. The reaction temperature, the combustion front velocity,and the product gas composition for both tests were similar, except that theair test had a lower oxygen utilization. The fuel consumptions were practicallythe same for both runs. This was expected practically the same for both runs.This was expected since the temperature profiles in both runs were nearlyidentical and the fuel deposition process was largely a function oftemperature. The oxygen/fuel ratios were also the same, indicating that theelemental compositions of the fuel were identical. It therefore appeared thatsubstituting N2 in air with CO2 did not change the combustion characteristicsfor this oil.
The oil displacement vs. volume burned is shown in Fig. 2. The fill-in timefor the CO2/O2 run was a little longer because of a somewhat higher gassaturation. Once in production, the displacement rates in both runs were almostidentical. The injection pressure and pressure drop across the tube are shownin Fig. 3. In pressure drop across the tube are shown in Fig. 3. In both tests,the injection pressure was set at 250 psi [1.7 MPa] by regulating thebackpressure. The pressure drop started to increase shortly after ignition,indicating the formation of an oil bank ahead of the thermal front. It reacheda maximum at about 2 to 2.5 hours when the oil bank started producing. As seen,the air test had a higher pressure drop that was associated with a bank of oilat the pressure drop that was associated with a bank of oil at the originalviscosity, The oil bank in the CO2/O2 run, on the other hand, contained oil ata lower viscosity because of CO2 dissolution. As a result, less pressure dropwas required to displace the oil at the same rate.
The system pressure of the tests was rather low, only 250 psi [1.7 MPa],simulating conditions in a typical psi [1.7 MPa], simulating conditions in atypical California heavy oil reservoir.
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