Hot Stabilization of Oil from the Samotlor Field
Abstract Generated abstract
This study examines hot stabilization conditions for Samotlor crude oil aimed at obtaining a relatively narrow light hydrocarbon fraction suitable for chemical industry use. Using a 25 theoretical plate precision rectification column, the authors measured gas and distillate yields and determined component compositions by gas chromatography at stabilization endpoint temperatures of 40, 50, 60, and 70°C. The results show increasing removal of butanes and pentanes with temperature, but also a sharp rise in C6 and heavier components in the overhead fraction at 70°C. The paper concludes that stabilization at 50 to 60°C gives the most favorable balance, providing substantial debutanization and pentane enrichment while avoiding excessive loss of heavier gasoline-range hydrocarbons.
Full Text
HOT STABILIZATION OF OIL FROM THE SAMOTLOR FIELD
N. M. Smolyaninova, A. I. Levashova, V. A. Kuznetsova
(Presented by the Scientific-Methodological Seminar of KhTF)
The aim of the work is to determine conditions for oil stabilization that ensure the production of a more or less narrow fraction of definite composition satisfying the requirements of the chemical industry. The composition of this fraction will be determined by the specified depth of withdrawal: either debutanization only, or with partial topping; this can be achieved by rectification.
For oil stabilization a small standard column for precise rectification was used, with 25 theoretical plates. The installation diagram is shown in the figure.
The heating rate was regulated in such a way that one hour elapsed from the moment gas evolution began until it ended. This regime ensures sufficiently slow gas evolution at a rate of approximately 10–15 cm³ of gas per minute.
After gas evolution ended, the volume of water that had flowed out was measured, as were atmospheric pressure and the pressure and temperature of the gas in the gasometer; the gasometer was disconnected from the column, the gas was sent for analysis, and the column was brought to operating conditions in the usual manner.
After bringing the column to operating conditions, distillate was withdrawn into a receiver cooled with melting ice. When the specified withdrawal temperature was reached (before the end of withdrawal, the fraction was “squeezed out”), the receiver was disconnected and weighed, and the condensate was sent for analysis.
Analysis of the component composition of the gas was carried out on an “KhL-4” chromatograph (packing: TZK + 12% vaseline oil; carrier gas: helium; temperature: −40°C).
The composition of the distillate was determined by gas-liquid chromatography on a “KhROM-2” chromatograph using a capillary column 100 meters long (stationary phase: “VM-4” vacuum oil; carrier gas: nitrogen).
In all, four series of experiments were carried out at specified stabilization temperatures of 40°C, 50°C, 60°C, and 70°C. In each experiment, the yields of dissolved gas and distillate released upon reaching the specified temperature at the column head were determined.
When determining the gas yield, corrections were introduced for the elasticity of water vapor and the expanding volume of air in the system.
From the yield and component composition of the gas and distillate, the composition of the total overhead fraction (gas + distillate) liberated during stabilization up to the specified temperatures was calculated.
Figure 1. Diagram of the unit for hot separation of oil: 1—still; 2—rectification column; 3—total-condensation head; 4—calcium-chloride tube; 5—tube for discharging gas into the gas meter; 6—gas meter; 7—distillate receiver; 8—thermometer; 9—graduated cylinder; 10—rubber tube; 11—manometer
Table 1 gives the composition of the dissolved gases, from which it follows that Samotlor oil contains 2.69 wt.% gases through C₄ and 5.57 wt.% components through C₅.
The results of hot stabilization of the oil, presented in Table 2, show that at a temperature of 40°C more than 60% of hydrocarbons through C₄ and about 26% of pentanes are removed from their resources in the oil (Table 1).
Table 1
Composition and yield of gases and low-boiling hydrocarbons dissolved in Samotlor oil
| Hydrocarbons | Yield on oil, wt.% | C₂H₆ | C₃H₈ | i-C₄H₁₀ | n-C₄H₁₀ | i-C₅H₁₂ | n-C₅H₁₂ | Total |
|---|---|---|---|---|---|---|---|---|
| through C₄ | 2.59 | 0.5 | 16.0 | 17.5 | 66.0 | — | — | 100.0 |
| through C₅ | 5.57 | 0.2 | 7.4 | 8.5 | 32.0 | 2.09 | 31.0 | 100.0 |
Table 2
Results of hot stabilization of Samotlor oil (well 14)
| Component | 40°C: in fraction | 40°C: in oil | 50°C: in fraction | 50°C: in oil | 60°C: in fraction | 60°C: in oil | 70°C: in fraction | 70°C: in oil |
|---|---|---|---|---|---|---|---|---|
| Ethane | 0.33 | 0.01 | 0.24 | 0.01 | 0.21 | 0.01 | 0.15 | 0.01 |
| Propane | 1.78 | 0.36 | 9.47 | 0.39 | 8.67 | 0.41 | 6.43 | 0.44 |
| Isobutane | 10.42 | 0.32 | 8.50 | 0.35 | 8.46 | 0.40 | 6.29 | 0.43 |
| n-Butane | 30.62 | 0.94 | 26.21 | 1.08 | 24.95 | 1.18 | 19.88 | 1.36 |
| Isopentane | 19.87 | 0.61 | 25.00 | 1.03 | 22.83 | 1.08 | 16.08 | 1.10 |
| n-Pentane | 23.72 | 0.73 | 26.70 | 1.10 | 27.27 | 1.29 | 21.05 | 1.44 |
| C₆ and higher | 3.26 | 0.10 | 3.88 | 0.16 | 7.61 | 0.36 | 30.12 | 2.06 |
| Total: | 100.00 | 3.07 | 100.00 | 4.12 | 100.00 | 4.73 | 100.00 | 6.84 |
| Total up to C₄ | 53.15 | 1.63 | 44.42 | 1.83 | 42.29 | 2.00 | 32.75 | 2.24 |
| up to C₅ | 96.74 | 2.97 | 96.12 | 3.96 | 92.39 | 4.37 | 69.88 | 4.78 |
With an increase in the final stabilization temperature, the content of heavy components in the overhead fraction increases: thus, at a temperature of 40°C the amount of hydrocarbons up to C₆ and higher is 3.26%, whereas at 70°C it is 30.12%, i.e., it increases almost tenfold.
It should be noted that even at a final withdrawal temperature of 70°C, complete debutanization is not observed (more than 10% of the C₄ resources remains in the oil).
Apparently, under the given conditions of oil stabilization, temperatures of 50°C and 60°C should be considered optimal, since they provide sufficiently good debutanization and significant enrichment of the fraction with pentanes. A temperature of 70°C cannot be recommended, since it causes the appearance of large quantities of heavy hydrocarbons in the stabilization fraction: the content of components C₆ and higher is 30.12% of the fraction, or 2.06% calculated on the oil. Such a regime will lead to a decrease in the gasoline potential of the oil.
Conclusions
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Hot stabilization of Samotlor oil was carried out by the method of sharp rectification.
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It has been shown that the optimal oil-stabilization temperature lies within the range of 50–60°C.