Physical Properties of Oil from the Lotyn-Yakh Field
Abstract Generated abstract
This paper reports laboratory determination of the physical properties of reservoir oil from the Lotyn-Yakh field in Tomsk Oblast, using a sample collected from well 63 in July 1974. The authors apply an established procedure with an added calculation method to improve estimation of the final volume of degassed oil, addressing errors caused by prolonged gas release during degassing. The measured properties include saturation pressure, compressibility, gas content, formation volume factor, shrinkage, density, gas density, solubility coefficient, and viscosity at reservoir and standard conditions. The results indicate that Lotyn-Yakh oil is closely similar to oils from the Pervomaisk and Vesenneye fields, especially in gas content and formation volume factor, supporting the view that these pools may be related, while other properties remain typical for Tomsk Oblast oils.
Full Text
PHYSICAL PROPERTIES OF OIL FROM THE LOTYN-YAKH FIELD
L. A. Pukhlyakov, V. V. Beloshapkina
(Presented by the Department of Combustible Minerals)
The Lotyn-Yakh structural uplift is located in the northwestern part of Tomsk Oblast, near the Pervomaisk and Vesenneye structural uplifts. Commercial oil was obtained here in 1964 by the Western Petroleum Exploration Expedition of the Tomsk Territorial Geological Administration. In the opinion of some geologists [1], the oil pool of the Lotyn-Yakh field is a single whole with the oil pools of the Pervomaisk and Vesenneye fields.
A sample of reservoir oil for determining physical properties from the Lotyn-Yakh field was taken in July 1974 and analyzed in November of the same year. The analysis was carried out according to the procedure set forth by V. N. Mamuna et al. [2] and somewhat supplemented by the authors.
This supplement was necessitated by the following circumstance. When determining the final volume of degassed oil, because gas continues to be released from it in small quantities for a very long time, there was always difficulty in determining the final oil volume. Until then, the final measurement had been made two or three times and at pressures, as a rule, above zero. As a result, a certain error was admitted in determining the final volume, and this led to errors in determining the volume coefficient.
To eliminate this shortcoming, use was made of the circumstance that at high pressures the volume of gas decreases significantly. Accordingly, the volume of degassed oil at reservoir pressure \(V_{\text{pl}}\) was taken as the basis for the calculation, and to it was added the so-called final increment \(\Delta V_k\), obtained from the increments in volume due to expansion as the pressure was reduced. The calculation was made according to the formula
\[ \Delta V_k = \frac{\Delta V_1 \cdot P_{\text{pl}}}{\Delta P_1}, \tag{1} \]
where \(\Delta V_1\) is the increase in volume in cm\(^3\) at a certain pressure drop \(\Delta P_1\), and \(P_{\text{pl}}\) is the final pressure drop in atm. Let us consider this with specific figures.
At a temperature of 20°C and reservoir pressure, the degassed oil had a volume of 90.50 cm\(^3\) on the press scale, and at the same temperature and a pressure of 40 atm, 94.14 cm\(^3\). Thus, the increase in volume
Table 1
Initial data for determining the final volume of oil after its degassing at 20°C
| Pressure in the press, ati | Volume by the press scale, cm³ | Increase in volume due to pressure reduction, cm³ |
|---|---|---|
| \(P\) | \(V\) | \(\Delta V_1\) |
| 254,5 | 90,50 | 0,00 |
| 200,0 | 91,34 | 0,84 |
| 160,0 | 91,98 | 1,48 |
| 120,0 | 92,64 | 2,14 |
| 80,0 | 93,36 | 2,86 |
| 40,0 | 94,14 | 3,64 |
| 20,0 | 94,60 | 4,10 |
at this stage \(\Delta V_1\) amounted to 3,64 cm³ (Table 1). Substituting these data into formula (1), we obtain
\[ \Delta V_k=\frac{3{,}64 \cdot 254{,}5}{254{,}5-40}=4{,}32\ \text{cm}^3. \tag{2} \]
At a pressure of 20 ati and under the same conditions, the volume of the sample by the press scale was 94,60 cm³, the volume increase was 4,1 cm³, and the final increase was 4,45 cm³. The average between them is 4,38 cm³, and the final volume at atmospheric pressure is expressed by the relation
\[ V_k=90{,}50+4{,}38+40=141{,}9\ \text{cm}^3, \tag{3} \]
where 40 is the dead volume of the apparatus.
The volume of non-degassed oil at a temperature of 95°C and reservoir pressure was 168,7 cm³. Hence the formation volume factor proved to be 1,189. The results of the study of other properties of the oil from the Lontyn-Yakh field are given in Table 2.
Table 2
Main physical properties of the oil from the Lontyn-Yakh field
(well 63, reservoir temperature 95°C, reservoir pressure 254,5 ati)
| No. | Parameters | Units of measurement | Results |
|---|---|---|---|
| 1 | Date of sampling | 9 July 1974 | |
| 2 | Perforation interval | m | 2476—2483 |
| 3 | Saturation pressure at reservoir temperature | ati | 60 |
| 4 | Average compressibility coefficient | \(10^{-5}\) 1/at | 17,35 |
| 5 | Gas content, referred to unit volume | m³/m³ | 39,72 |
| 6 | Gas content, referred to unit weight | m³/t | 46,45 |
| 7 | Formation volume factor | 1 | 1,189 |
| 8 | Shrinkage | % | 15,90 |
| 1 | 2 | 3 | 4 |
|---|---|---|---|
| 9 | Density of separated oil at 20°C | g/cm³ | 0.855 |
| 10 | Density of dead oil at 95°C | g/cm³ | 0.761 |
| 11 | Average gas density at 20°C and 760 mm Hg | g/liter | 1.240 |
| 12 | Average coefficient of gas solubility | m³/m³·atm | 0.650 |
| 13 | Viscosity of separated oil at 20°C | cP | 6.23 |
| 14 | Viscosity of separated oil at 95°C | cP | 1.49 |
| 15 | Final degassing pressure | mm Hg | 757 |
| 16 | Final degassing temperature | °C | 20°C |
| 17 | Date of completion of the analysis | 30 November 1974 |
In terms of its physical properties, the oil of the Lotyn-Yakh field is identical to the oil of the Pervomaiskoe and Vesennee fields. In any case, both there and here the gas content of the oil is close to 40 m³/m³. These oils are especially close in volume factor. For the oil of the Vesennee field it is equal to 1.209, for the oil of the Pervomaiskoe field, 1.181, and for the oil of the Lotyn-Yakh field, 1.189. For comparison, it may be noted that the oil of the Olen’e field has a volume factor of 1.29 and a gas content of about 76 m³/m³. This is understandable: if the oil pool of the Lotyn-Yakh field forms a single whole with the oil pools of the Pervomaiskoe and Vesennee fields, then a certain similarity of their characteristics should be present.
It should be noted here, however, that with respect to other characteristics (density, viscosity, compressibility), the oils of the Lotyn-Yakh, Pervomaiskoe, and Vesennee fields do not stand out among the other oils of Tomsk Oblast.
REFERENCES
-
A Course toward Increasing Efficiency. Newspaper Krasnoe znamya, No. 162 (15459), Tomsk, 13 July 1974.
-
V. N. Mamuna, G. F. Trebin, V. V. Ul’yaninskii. Experimental Study of Reservoir Oils. Moscow, GOSINTI, 1960.