Balance of Gas-Exchange and Light Hydrocarbons in Reservoir Oils of the Samotlor Field
Abstract Generated abstract
This paper quantifies the distribution of gaseous and light hydrocarbon components released during stepwise degassing of bottomhole reservoir oil samples from the Samotlor field in Western Siberia. Using measurements of individual gas composition, gas volume, density, and residual dissolved gases at reservoir temperature, the authors compile component balances per ton of reservoir oil for wells in reservoirs A-I and B-VIII. The results show that methane, ethane, and non-hydrocarbon gases are released mainly at the initial separation pressure, while most C3 to C5 hydrocarbons are recoverable during later pressure reduction and stabilization. The calculated total C3 to C5 yields are 54.48 kg/t for well 14 and 83.99 kg/t for well 12, indicating a substantial potential petrochemical raw material resource.
Full Text
Balance of Gaseous and Light Hydrocarbons in Reservoir Oils of the Samotlor Field
A. V. Kravtsov, N. M. Smolyaninova
(Presented by the scientific-methodological seminar of the KhTF)
During stepwise degassing of reservoir oil from the Samotlor field, a significant amount of gas is released, containing
Balance of gas components during stepwise degassing of reservoir oil
| Component | 60: in gas phase | 60: dissolved in oil | 40: in gas phase | 40: dissolved in oil | 20: in gas phase | 20: dissolved in oil |
|---|---|---|---|---|---|---|
| Methane | 37,30 | 30,94 | 47,85 | 20,39 | 56,90 | 11,34 |
| Ethane | 0,92 | 3,95 | 1,31 | 3,56 | 1,99 | 2,88 |
| Propane | 2,07 | 11,57 | 2,92 | 10,72 | 3,92 | 9,72 |
| Isobutane | 0,69 | 6,21 | 0,90 | 6,00 | 1,34 | 5,56 |
| n-Butane | 1,27 | 10,25 | 1,61 | 10,25 | 2,49 | 9,37 |
| Isopentane | 0,36 | 9,21 | 0,46 | 9,08 | 0,76 | 8,81 |
| n-Pentane | 0,41 | 12,10 | 0,55 | 11,96 | 0,76 | 11,75 |
| Nitrogen | 1,61 | 0,85 | 1,97 | 0,49 | 2,26 | 0,20 |
| Acid gases | 0,22 | 0,43 | 0,31 | 0,34 | 0,46 | 0,19 |
| Total: | 44,90 | 87,03 | 57,70 | 74,23 | 70,80 | 61,13 |
Note: In the balance it is necessary to account for \(C_6 = 1,2\) kg/t, released in
Balance of gas components during stepwise degassing of reservoir oil
| Component | 60: in gas phase | 60: dissolved in oil | 40: in gas phase | 40: dissolved in oil | 20: in gas phase | 20: dissolved in oil |
|---|---|---|---|---|---|---|
| Methane | 20,25 | 34,55 | 30,40 | 24,40 | 37,40 | 17,40 |
| Ethane | 1,02 | 7,29 | 1,79 | 6,52 | 2,72 | 5,59 |
| Propane | 1,38 | 27,43 | 2,76 | 26,05 | 4,57 | 24,24 |
| Isobutane | 0,21 | 7,44 | 0,44 | 7,21 | 0,72 | 6,93 |
| n-Butane | 0,26 | 21,11 | 0,57 | 20,80 | 1,26 | 20,11 |
| Isopentane | 0,14 | 10,80 | 0,26 | 10,68 | 0,43 | 10,51 |
| n-Pentane | 0,18 | 15,04 | 0,32 | 14,90 | 0,48 | 14,74 |
| Nitrogen | 0,70 | 0,94 | 1,10 | 0,54 | 1,56 | 0,08 |
| Acid gases | 0,17 | 0,65 | 0,36 | 0,46 | 0,66 | 0,16 |
| Total | 24,80 | 128,23 | 37,80 | 115,27 | 51,80 | 101,27 |
Note. In the component balance it is necessary to account for \(C_6 = 3,46\) kg/t, released
valuable raw material for the petrochemical industry—hydrocarbons \(C_2—C_5\). In order to calculate the resources of these components in a bottomhole oil sample, on the basis of the results of work to determine the individual composition, volume, and density of the separation gas, a balance of the hydrocarbons of the oil and gas was carried out during stepwise degassing of the reservoir oil.
Determination of the quantity and composition of gases remaining in the dissolved state after stepwise degassing of bottom-hole oil samples at reservoir temperature (2.243 wt.% for reservoir A-I and 3.027 wt.% for reservoir B-VIII) made it possible to determine the total amount of gas (up to C₅) in the reservoir oil (13.193 wt.% and 15.307 wt.%, respectively), as well as the weight content of free gas and gas in solution during a stepwise pressure drop in the system.
Taking these data into account, the balance of gas components during stepwise degassing of oil from the wells studied was calculated per 1 ton of reservoir oil. The results are presented in Tables 1 and 2.
It can be seen that during oil separation at 6 ati, the main quantities of methane, ethane, and non-hydrocarbon gases are released from the reservoir oil.
The overwhelming part of the C₃—C₅ hydrocarbons can be recovered and used during separation of oil from 6 to 0 ati and during its subsequent stabilization.
Table 1
from well 14 (per 1 t of reservoir oil), kg/t
| 16 ati: in gas phase | 16 ati: dissolved in oil | 5 ati: in gas phase | 5 ati: dissolved in oil | 0 ati: in gas phase | 0 ati: dissolved in oil | Total |
|---|---|---|---|---|---|---|
| 59,35 | 8,81 | 63,38 | 4,86 | 68,24 | 0,00 | 68,24 |
| 2,21 | 2,66 | 2,90 | 1,97 | 4,86 | 0,01 | 4,87 |
| 4,36 | 9,28 | 6,24 | 7,40 | 12,50 | 1,14 | 13,64 |
| 1,45 | 5,45 | 1,86 | 5,04 | 5,82 | 1,08 | 6,90 |
| 2,69 | 9,17 | 3,63 | 8,23 | 6,49 | 5,37 | 11,86 |
| 0,82 | 8,75 | 1,09 | 8,48 | 3,69 | 5,88 | 9,57 |
| 0,81 | 11,70 | 1,13 | 11,38 | 3,56 | 8,95 | 12,51 |
| 2,33 | 0,13 | 2,39 | 0,07 | 2,46 | 0,00 | 2,46 |
| 0,47 | 0,18 | 0,51 | 0,14 | 0,65 | 0,00 | 0,65 |
| 74,40 | 57,53 | 83,40 | 48,53 | 109,50 | 22,43 | 131,93 |
[[unclear: beginning of footnote]] gas phase at the 8th stage.
Table 2
from well 12 (per 1 t of reservoir oil), kg/t
| 16 ati: in gas phase | 16 ati: dissolved in oil | 6 ati: in gas phase | 6 ati: dissolved in oil | 0 ati: in gas phase | 0 ati: dissolved in oil | Total |
|---|---|---|---|---|---|---|
| 43,70 | 11,10 | 49,47 | 5,31 | 54,80 | 0,00 | 54,80 |
| 3,42 | 4,89 | 4,78 | 3,53 | 8,26 | 0,05 | 8,31 |
| 6,15 | 22,66 | 9,80 | 19,01 | 27,00 | 1,81 | 28,81 |
| 1,08 | 6,57 | 1,79 | 5,86 | 6,04 | 1,61 | 7,65 |
| 1,86 | 19,51 | 3,38 | 17,99 | 13,00 | 8,37 | 21,37 |
| 0,58 | 10,36 | 0,98 | 9,96 | 4,01 | 6,93 | 10,94 |
| 0,66 | 14,56 | 0,94 | 14,28 | 3,72 | 11,50 | 15,22 |
| 1,64 | 0,00 | 1,64 | 0,00 | 1,64 | 0,00 | 1,64 |
| 0,72 | 0,10 | 0,76 | 0,06 | 0,82 | 0,00 | 0,82 |
| 60,30 | 92,77 | 78,67 | 74,40 | 123,00 | 30,07 | 153,07 |
[[unclear: beginning of footnote]] in the gas phase at the 7th stage.
Conclusions
-
A balance has been compiled for the components of the gas released during stepwise degassing of a bottom-hole oil sample from the Samotlor field of Western Siberia.
-
It has been shown that the total amount of C₃—C₅ hydrocarbons released from 1 t of reservoir oil from well 14 (reservoir A-I) and well 12 (reservoir B-VIII) is, respectively, 54.48 and 83.99 kg.