PROCEEDINGS
OF THE TOMSK ORDER OF THE OCTOBER REVOLUTION
AND ORDER OF THE RED BANNER OF LABOR
POLYTECHNIC INSTITUTE NAMED AFTER S. M. KIROV

Vol. 253　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1976

PHYSICAL PROPERTIES OF THE OIL OF THE PERVOMAISK FIELD

L. A. Pukhlyakov, G. N. Chertenkova

(Presented by Professor A. V. Aksarin)

In the petroleum-reservoir physics laboratory, using the UIPN-2M apparatus, a study was made of the properties of the oil of the Pervomaisk field in Tomsk Oblast. For this purpose an oil sample was taken from well 260 from reservoir Yu-1 of the Vasyugan suite of Upper Jurassic age. The reservoir pressure in this well at the moment the sample was taken was 251.8 atm, and the reservoir temperature was 89°C.

The study was begun with determination of the saturation pressure \(P_s\). The work was carried out according to the procedure set forth by V. N. Mamuna et al. [1]. The results of the study of this parameter are shown in Fig. 1, from which it is evident that the saturation pressure for reservoir Yu-1 of the Pervomaisk field is 74 atm.

Next the coefficient of compressibility of the oil \(\alpha\) was determined. The study was conducted in the interval between the reservoir pressure and a pressure somewhat above the saturation pressure. This value proved to be equal to \(17.72 \cdot 10^{-5}\ \text{atm}^{-1}\).

The amount of gaseous and vaporous hydrocarbons and nonhydrocarbon compounds released from the reservoir oil in the process of reducing the pressure in it to atmospheric pressure, referred to a unit of volume or weight, is called the gas content. This quantity is denoted by the symbol \(f_v\) if the gas content is referred to a unit of volume, and by the symbol \(f_G\) if the gas content is referred to a unit of weight.

The value of the gas content was determined in the process of so-called single-stage degassing, which consisted in the following: a certain quantity of oil was released from the press, and it was immediately degassed in a separator. The quantity of gas was measured in a gas burette, and the quantity of oil in the measuring vessel of the separator. The gas content referred to a unit of volume proved to be \(42.36\ \text{cm}^3/\text{cm}^3\).

The separated oil was weighed, which made it possible to determine its density \(\gamma_{\text{s.n.}}\), which proved to be \(0.837\ \text{g}/\text{cm}^3\), and the gas content referred to a unit of weight, \(f_G\), which proved to be \(50.61\ \text{cm}^3/\text{g}\).

After measuring the volume of gas in the gas burette, a sample was taken from it for analysis and for determination of density. The density of the gas of the Pervomaisk field proved to be \(1.302\ \text{g}/\text{liter}\).

Closely connected with gas content is the concept of the coefficient of solubility of gas in oil \(\alpha\), which characterizes the amount of gas capable of dissolving in a unit of volume or weight of separated oil.

Fig. 1. Graph for determining saturation pressure

when the pressure is increased by one atmosphere. This quantity is determined by the formula

\[ a=\frac{f}{P_s}, \tag{1} \]

where \(f\) is the gas content, and \(P_s\) is the saturation pressure. The gas solubility coefficient for the oil of the Pervomaiskoye field was found to be \(0.572\ \mathrm{cm}^3/\mathrm{cm}^3\) atm.

The presence of dissolved gas in the oil and the elevated temperature lead to the fact that, under reservoir conditions, the oil occupies a larger volume than at the surface after separation. The ratio of these volumes is usually called the oil formation volume factor and is denoted by the letter \(b\). The oil formation volume factor for the Pervomaiskoye field proved to be 1.181.

To characterize the change in oil volume when it passes from reservoir conditions to surface conditions, another quantity is sometimes used—the oil shrinkage \(u\), which shows by how many percent the oil volume decreases when it passes from reservoir conditions to surface conditions. This quantity is determined by the formula

\[ u=\frac{b-1}{b}\,100. \]

The oil shrinkage for the Pervomaiskoye field proved to be 15.33%.

Next, the oil density under reservoir conditions was determined. The calculation was made by the formula

\[ \gamma_{\mathrm{pl}}=\frac{\gamma_{\mathrm{sn}}}{b}+\frac{f_v\cdot \rho_{\mathrm{g}}}{1000b}. \]

The average value of this parameter for the oil of the Pervomaiskoye field proved to be 0.764 g/cm\(^3\).

Special attention was devoted to studying the viscosity of the oil. At first this parameter was determined for the oil in the non-degassed state under reservoir conditions, i.e., at a pressure of 251.8 atm and a temperature of 89°C. The average value of this parameter proved to be 0.71 centipoise. In addition, the viscosity of the non-degassed oil was determined at pressures of 200 atm, 150 atm, and 100 atm and at temperatures of 27°C, 40°C, and 60°C (Table 1). As a result of this investigation it was established that, with decreasing pressure, the viscosity of the oil decreases, and with decreasing temperature it increases.

Table 1

Results of the investigation of the viscosity of oil from the Pervomaiskoye field in the non-degassed state

Next, the viscosity of the oil was determined in the partially degassed state. In this case, the first oil sample was degassed first at a pressure of 10 atm, then at a pressure of 5 atm (Table 2), and the second sample at pressures of 50 and 20 atm. As a result of this investigation it was established that, as the degassing pressure decreases, the viscosity of the oil gradually increases (Table 3).

The viscosity of completely degassed oil was also determined. For the first sample this parameter proved to be 5.21, for the second—5.05, and the average value was 5.13 centipoise.

Table 2

Results of the investigation of the viscosity of oil from the Pervomaiskoye field
in a partially degassed state

REFERENCES

1. V. N. Mamuna, G. F. Trebin, B. V. Ulyaninsky. Experimental Investigation of Reservoir Oils. GOSINTI, Moscow, 1960.