Study of the Component Composition of Associated Gas from the Sovetskoye Oil Field
Abstract Generated abstract
This study evaluates the resources and component composition of associated petroleum gas from the Sovetskoye oil field in Western Siberia, where rising oil production was expected to generate large gas volumes. Bottom-hole oil samples from productive strata A-I and B-VIII were subjected to staged degassing, and the released gases were analyzed chromatographically, with carbon dioxide measured by chemical gas analysis. The experiments found gas saturation pressures of about 80 to 100 atm and total gas yields of 45.68 to 56.23 m³ per m³ of oil, with broadly similar gas compositions in the two strata but lower overall gas content in A-I. As pressure decreased, methane content fell and the propane to pentane fraction increased substantially, indicating a significant potential petrochemical resource.
Full Text
STUDY OF THE COMPONENT COMPOSITION OF ASSOCIATED GAS FROM THE SOVETSKOYE OIL FIELD
A. V. KRAVTSOV, V. A. KUZNETSOVA, N. M. SMOLYANINOVA
(Presented by the scientific-methodological seminar of the KhTF)
In 1967, one of the largest oil fields in the Soviet Union, the Sovetskoye field, located in Tomsk Oblast, was put into pilot operation. In 1970 the amount of oil produced here was 3.4 million tons, and by 1975 it will increase to 10 million tons.
Oil production is accompanied by a significant release of associated gases (about 55 m³/t of oil) and stabilization gases (dissolved in the oil), which are a valuable raw material for the petrochemical industry.
The purpose of the present work is to determine the resources and component composition of the associated petroleum gas of the Sovetskoye field.
For the study, bottom-hole oil samples were taken from the productive strata A-1 (well 17) and B-VIII (wells 501 and 27) at pressures from 170 to 220 ati and temperatures from 53 to 73°C (Table 1). These samples were subjected to stepwise degassing1 on the UIPN-2M unit according to a known procedure.2
Stepwise separation of oil is at present one of the progressive methods for collecting associated gases during the operation of large oil fields. It makes it possible to separate the gas into a “dry gas,” less valuable for petrochemistry, and transport it to the consumer under its own pressure, and a “wet gas,” containing the maximum amount of the propane-pentane fraction.
The results of the experiments are given in Table 2. They made it possible to establish that, for all the studied wells of stratum A-1 and stratum B-VIII, the pressure of oil saturation with gas lies within the range of 80–100 atm. The total amount of gas released per 1 m³ of oil during its contact degassing, for samples from wells 17, 501, and 27, is respectively 45.68 m³; 50.96 m³; 56.23 m³, or, respectively, in weight percent based on the initial formation sample—4.88%; 5.42%; 5.84%.
Gas sampling during stepwise degassing of the bottom-hole samples was carried out differentially, i.e., into separate vessels for each stage. Analysis of the selected gas samples was performed by the chromatographic method. Determination of the carbon dioxide content in the gas was carried out—
Table 1
Characteristics of the points for sampling reservoir oil samples from the Sovetskoye field
| No. | Well No. | System | Suite | Bed | Perforation interval, m | Well operating regime: oil production rate, t/day | Well operating regime: reservoir pressure, atm | Well operating regime: reservoir temperature, °C | Well operating regime: oil saturation pressure with gas, atm | Sampling location |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 17 | — | Vartovskaya | A-I | 1636—1690 | 80 | 171,2 | 53,0 | 84,0 | Top of horizon A-I |
| 2 | 501 | Cretaceous | Kulomzinskaya | B-III | 2156—2159 | 130 | 218,8 | 72,5 | 98,0 | Top of horizon B-VIII |
| 3 | 27 | Cretaceous | Kulomzinskaya | B-VIII | 2144—2153 | 305 | 216,8 | 73,0 | 102,0 | Top of horizon B-VIII |
Table 3
Results of stepwise degassing of a bottom-hole oil sample from the Sovetskoye field, wt. %
| Indicators | Well No. | \(P_{\text{pl.}}\) | I | II | III | IV |
|---|---|---|---|---|---|---|
| Pressure, atm | 17 | 171,2 | 25,0 | 16,5 | 8,2 | 0,0 |
| Pressure, atm | 501 | 218,8 | 25,0 | 8,2 | 0,0 | |
| Pressure, atm | 27 | 216,8 | 20,0 | 8,2 | 0,0 | |
| Conditions of measurement and gas sampling: \(P\) mm Hg/\(T_{\text{com}}^\circ\mathrm{C}\) | 17 | — | 740/20 | 740/20 | 740/20 | 740/20 |
| Conditions of measurement and gas sampling: \(P\) mm Hg/\(T_{\text{com}}^\circ\mathrm{C}\) | 501 | — | 763/20 | 763/20 | 763/20 | |
| Conditions of measurement and gas sampling: \(P\) mm Hg/\(T_{\text{com}}^\circ\mathrm{C}\) | 27 | — | 746/19 | 746/19 | 746/19 | |
| Specific amount of gas released by stages, cm³/cm³ | 17 | 0,00 | 25,26 | 4,48 | 4,34 | 8,47 |
| Specific amount of gas released by stages, cm³/cm³ | 501 | 0,00 | 30,30 | 8,25 | 8,81 | |
| Specific amount of gas released by stages, cm³/cm³ | 27 | 0,00 | 34,55 | 6,97 | 9,76 | |
| Gas content of oil at \(P = 1\) ata, m³/m³ | 17 | — | — | — | — | 45,68 |
| Gas content of oil at \(P = 1\) ata, m³/m³ | 501 | — | — | — | 50,96 | |
| Gas content of oil at \(P = 1\) ata, m³/m³ | 27 | — | — | — | 56,23 | |
| Gas density by stages (0°C and 760 mm Hg), g/l | 17 | — | 0,868 | 0,885 | 0,965 | 1,471 |
| Gas density by stages (0°C and 760 mm Hg), g/l | 501 | — | 0,844 | 0,997 | 1,542 | |
| Gas density by stages (0°C and 760 mm Hg), g/l | 27 | — | 0,874 | 1,008 | 1,482 | |
| Oil density, g/cm³ | 17 | 0,773 | 0,775 | 0,776 | 0,786 | 0,797 |
| Oil density, g/cm³ | 501 | 0,765 | 0,772 | 0,786 | 0,804 | |
| Oil density, g/cm³ | 27 | 0,760 | 0,769 | 0,787 | 0,803 | |
| Amount of gas released, wt. % | 17 | 0,00 | 2,31 | 0,59 | 0,58 | 1,40 |
| Amount of gas released, wt. % | 501 | 0,00 | 3,00 | 0,87 | 1,55 | |
| Amount of gas released, wt. % | 27 | 0,00 | 3,40 | 0,81 | 1,63 | |
| Amount of remaining oil, wt. % | 17 | 100,00 | 97,69 | 97,10 | 96,52 | 95,12 |
| Amount of remaining oil, wt. % | 501 | 100,00 | 97,00 | 96,13 | 94,58 | |
| Amount of remaining oil, wt. % | 27 | 100,00 | 96,60 | 95,79 | 94,16 |
was carried out on a VTI-2 chemical gas analyzer. The results of the analyses are presented in Table 3.
As was to be expected, the methane content in the associated gas decreases significantly, while the content of \(C_3\)—\(C_5\) hydrocarbons increases as the pressure in the system decreases.
For all the wells studied, taking into account the amount of gas released at each stage, the component composition of the associated gases during stepwise degassing of the oil was recalculated to the total volume.^3 The results of the recalculations, presented in Table 3, make it possible to note that the above-indicated regularities in the change of the component composition of associated gas during stepwise degassing of bottom-hole oil samples are retained, although to a considerable degree they are leveled out.
The composition of the associated gas from reservoir A-1 (well 17) and reservoir B-VIII (wells 27 and 501) is practically identical, but the gas content of the oil as a whole from reservoir A-1 is lower than that of reservoir B-VIII. The content of \(C_3\)—\(C_5\) hydrocarbons in the associated gas increases significantly with a decrease in
^3 A. S. Smirnov, A. I. Shirkovskii, Gas Production and Transportation. Gostoptekhizdat, 1967.
Table 3
Gas composition during staged degassing of reservoir oil from the Sovetskoye field, wt. %
| Components | Well No. | I stage: gas composition at stage | II stage: at stage | II stage: in total volume | III stage: at stage | III stage: in total volume | IV stage: at stage | IV stage: in total volume |
|---|---|---|---|---|---|---|---|---|
| Methane | 17 | 72,2 | 70,0 | 71,8 | 60,2 | 70,8 | 24,3 | 59,6 |
| Methane | 501 | 73,2 | 58,3 | 70,0 | 29,5 | 59,2 | 24,3 | 59,6 |
| Methane | 27 | 71,4 | 59,1 | 69,7 | 22,8 | 57,3 | 24,3 | 59,6 |
| Ethane | 17 | 5,0 | 5,2 | 5,2 | 6,7 | 5,4 | 7,8 | 6,4 |
| Ethane | 501 | 5,8 | 8,0 | 6,1 | 8,5 | 6,9 | 7,8 | 6,4 |
| Ethane | 27 | 4,9 | 6,5 | 5,2 | 7,6 | 6,1 | 7,8 | 6,4 |
| Propane | 17 | 9,1 | 11,2 | 9,3 | 15,7 | 10,1 | 31,3 | 12,5 |
| Propane | 501 | 7,4 | 13,1 | 8,7 | 21,6 | 12,0 | 31,3 | 12,5 |
| Propane | 27 | 6,8 | 15,1 | 9,6 | 9,3 | 13,7 | 31,3 | 12,5 |
| i-Butane | 17 | 2,4 | 2,3 | 2,4 | 3,8 | 2,2 | 9,1 | 4,4 |
| i-Butane | 501 | 3,0 | 5,6 | 3,7 | 10,4 | 5,6 | 9,1 | 4,4 |
| i-Butane | 27 | 4,1 | 5,3 | 4,8 | 14,4 | 7,4 | 9,1 | 4,4 |
| n-Butane | 17 | 4,8 | 4,7 | 4,8 | 6,8 | 5,0 | 15,4 | 8,6 |
| n-Butane | 501 | 4,6 | 8,9 | 5,5 | 18,0 | 9,1 | 15,4 | 8,6 |
| n-Butane | 27 | 6,9 | 9,6 | 5,6 | 23,4 | 11,5 | 15,4 | 8,6 |
| i-Pentane | 17 | 1,5 | 1,5 | 1,5 | 2,0 | 1,6 | 6,0 | 2,9 |
| i-Pentane | 501 | 1,9 | 2,9 | 2,1 | 4,9 | 2,6 | 6,0 | 2,9 |
| i-Pentane | 27 | 1,1 | 1,0 | 1,0 | 0,9 | 0,6 | 6,0 | 2,9 |
| n-Pentane | 17 | 1,5 | 1,8 | 1,5 | 2,7 | 1,6 | 5,5 | 2,9 |
| n-Pentane | 501 | 1,5 | 3,2 | 2,1 | 6,7 | 3,0 | 5,5 | 2,9 |
| n-Pentane | 27 | 1,1 | 1,3 | 1,0 | 1,1 | 0,9 | 5,5 | 2,9 |
| Nonhydrocarbon gases (N₂ + CO₂ + rare gases) | 17 | 3,5 | 3,3 | 3,5 | 2,1 | 3,3 | 0,6 | 2,7 |
| Nonhydrocarbon gases (N₂ + CO₂ + rare gases) | 501 | 2,6 | 0,4 | 1,9 | 0,4 | 1,6 | 0,6 | 2,7 |
| Nonhydrocarbon gases (N₂ + CO₂ + rare gases) | 27 | 3,7 | 2,1 | 3,1 | 0,5 | 2,5 | 0,6 | 2,7 |
pressure in the system is below 8–10 ati and reaches 31–34 wt. % (when the gas is collected into the total volume).
With an increase in oil production by 1975 to 10 million tons at the Sovetskoye field, more than half a billion cubic meters of associated gas will be obtained and, thus, about 200 thousand tons of hydrocarbons C₃–C₅.
Conclusions
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Staged degassing was carried out on bottom-hole oil samples from productive strata A-I and B-VIII of the Sovetskoye oil field in Western Siberia.
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The component composition of associated gas during staged degassing of reservoir oil samples was determined under the condition that it is collected at each stage and into the total volume.