Resources and Composition of Light Hydrocarbons (C1-C5) in a Reservoir Sample of Typical Oil
Abstract Generated abstract
This paper examines the resources and composition of light hydrocarbons in a reservoir sample representing typical oil from several Western Siberian fields. A blended reservoir sample was subjected to stepwise degassing, with gas yields, densities, and hydrocarbon compositions measured at successive pressure reductions and used to calculate a component balance for C1 to C5 hydrocarbons per tonne of reservoir oil. The results show that more than half of the gas is released by 30 atm and about 92.5 percent by 4.5 atm, while methane decreases and C3 to C5 hydrocarbons become relatively more important as pressure falls. The study indicates that most methane and nonhydrocarbon gases are removed by separation to 4.5 atm, whereas much of the C3 to C5 fraction may be recovered during final pressure reduction and subsequent oil stabilization.
Full Text
Resources and Composition of Light Hydrocarbons (C₁—C₅) in a Reservoir Sample of Typical Oil
N. M. Smolyaninova, A. V. Kravtsov
(Presented by the Scientific-Methodological Seminar of the Organic Departments)
To determine the resources and composition of the broad hydrocarbon fraction of a typical oil, stepwise degassing of its reservoir sample was carried out.
To prepare the typical oil, reservoir samples of oils from the Samotlor, Sovetskoe, Megion, and Var'egan fields of Western Siberia were selected. The reservoir sample was blended on a UIPN-2M unit, guided by data from “Giprotyumenneftegaz” on reservoir oil production from the indicated fields for 1975.
In the degassing and subsequent calculations, the methods given in [1, 2] were used. The results of the stepwise degassing of the reservoir sample of typical oil are presented in Table 1, from which
Table 1
Results of stepwise degassing of a reservoir sample of typical oil from the fields of the Nizhne-Vartovsk arch
| Indicators | Unit of measurement | 211.0 reservoir | 93.0 | 76.5 | 59.0 | 45.0 | 30.5 | 21.0 | 9.5 | 4.5 | 1.0 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Gas content | m³/m³ | 64.00 | 64.00 | 54.73 | 43.68 | 36.13 | 27.81 | 19.66 | 9.58 | 4.55 | 0.00 |
| Gas content | m³/t | 75.92 | 75.92 | 64.92 | 51.81 | 42.86 | 32.99 | 23.32 | 11.37 | 5.40 | 0.00 |
| Gas factor | m³/m³ | 0.00 | 0.00 | 9.27 | 20.32 | 27.87 | 36.19 | 44.34 | 54.41 | 59.45 | 64.00 |
| Gas factor | m³/t | 0.00 | 0.00 | 10.99 | 24.10 | 33.05 | 42.92 | 52.60 | 64.55 | 70.52 | 75.92 |
| Gas density | g/L | — | — | 0.921 | 0.815 | 0.785 | 0.806 | 0.835 | 1.004 | 1.097 | 1.527 |
| Density* of reservoir oil | g/cm³ | 0.747 | 0.734 | 0.743 | 0.755 | 0.764 | 0.767 | 0.779 | 0.799 | 0.802 | 0.813 |
* Density of oil after stepwise degassing: 0.843 g/cm³.
it is evident that more than 50% of the gases are released when the pressure is reduced to 30 atm, and when the pressure is reduced to 4.5 atm, 92.5% of all components constituting the gas factor already pass into the gas phase.
As was to be expected, the methane content in the associated gas decreases, while the content of hydrocarbons C₃—C₅ increases as the pressure in the system decreases.
To compile the balance of light hydrocarbons in the reservoir sample of typical oil, the yield and composition of gases dissolved in the oil after its degassing to ...
atmospheric pressure at a temperature of 20°C. The results of the investigations, presented in Table 2, indicate that the degassed oil contains considerable quantities of heavy components—mainly \(C_4\)—\(C_5\).
Table 2
Composition of gas and light hydrocarbons dissolved in surface and reservoir samples of typical oil
| Well No. | Sampling depth | \(C_2H_6\), on surface oil | \(C_2H_6\), on reservoir oil | \(C_3H_8\), on surface oil | \(C_3H_8\), on reservoir oil | iso-\(C_4H_{10}\), on surface oil | iso-\(C_4H_{10}\), on reservoir oil | n-\(C_4H_{10}\), on surface oil | n-\(C_4H_{10}\), on reservoir oil | iso-\(C_5H_{12}\), on surface oil | iso-\(C_5H_{12}\), on reservoir oil | n-\(C_5H_{12}\), on surface oil | n-\(C_5H_{12}\), on reservoir oil | Total, on surface oil | Total, on reservoir oil |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Typical | to \(C_4\) | 0.011 | 0.61 | 0.400 | 0.47 | 0.394 | 0.58 | 1.398 | 1.78 | — | — | — | — | 2.203 | 4.44 |
| Typical | to \(C_5\) | 0.011 | 0.61 | 0.400 | 0.47 | 0.394 | 0.58 | 1.398 | 1.78 | 1.035 | 1.13 | 1.697 | 1.279 | 4.935 | 7.36 |
On the basis of data on the composition of the gases released during stepwise degassing of the reservoir sample of typical oil, and the data from Table 2, a balance of light hydrocarbons \(C_2\)—\(C_5\) for reservoir oil was calculated and compiled; it is presented in Table 3. It is evident that, at
Table 3
Balance of gas components during stepwise degassing of a reservoir oil sample
(calculated per 1 tonne of reservoir oil)
| 21.0 atm: in gas phase, kg/t | 21.0 atm: dissolved in oil, kg/t | 9.5 atm: in gas phase, kg/t | 9.5 atm: dissolved in oil, kg/t | 4.5 atm: in gas phase, kg/t | 4.5 atm: dissolved in oil, kg/t | 1.0 atm: in gas phase, kg/t | 1.0 atm: dissolved in oil, kg/t | Total |
|---|---|---|---|---|---|---|---|---|
| 37.37 | 11.04 | 44.49 | 3.92 | 47.40 | 1.01 | 48.41 | 0 | 48.41 |
| 2.36 | 3.71 | 3.38 | 2.49 | 4.57 | 1.50 | 5.96 | 0.11 | 6.07 |
| 3.29 | 11.49 | 5.24 | 9.54 | 6.99 | 7.79 | 10.78 | 4.00 | 14.78 |
| 0.59 | 5.25 | 0.93 | 4.91 | 1.24 | 4.60 | 1.90 | 3.94 | 5.84 |
| 1.24 | 16.56 | 1.96 | 15.84 | 2.49 | 15.31 | 3.82 | 13.98 | 17.80 |
| 0.35 | 10.92 | 0.54 | 10.73 | 0.67 | 10.60 | 0.92 | 10.35 | 11.27 |
| 0.43 | 17.52 | 0.64 | 17.31 | 0.74 | 17.21 | 0.98 | 16.97 | 17.95 |
| 0.29 | 0.28 | 0.44 | 0.13 | 0.50 | 0.07 | 0.57 | 0 | 0.57 |
| 1.51 | 0.04 | 1.56 | 0 | 1.55 | 0 | 1.55 | 0 | 1.55 |
| 0.42 | 0.39 | 0.57 | 0.24 | 0.71 | 0.10 | 0.81 | 0 | 0.81 |
| 47.85 | 77.20 | 59.94 | 65.11 | 66.86 | 58.19 | 75.70 | 49.35 | 125.05 |
separation down to 4.5 atm the main quantity of methane and nonhydrocarbon gases is released from the reservoir oil. Consequently, the predominant quantity of hydrocarbons \(C_3\)—\(C_5\) can be released during separation of the oil from 4.5 atm to atmospheric pressure and during its subsequent stabilization.
LITERATURE
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V. N. Mamuna, G. F. Trebin, B. V. Ulyaninsky. Experimental investigation of reservoir oils. Moscow, GOINITI, 1960.
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A. S. Smirnov, A. I. Shirkovsky. Gas production and transportation. Gostoptekhizdat, 1967.