ON THE VISCOSITY OF OIL FROM THE KLYUCHEVSKOYE FIELD IN TOMSK OBLAST UNDER RESERVOIR CONDITIONS

L. A. Pukhlyakov, G. N. Chertenkova

(Presented by Professor A. V. Aksarin)

When temperatures and pressures change, the viscosities of liquids do not remain constant. With increasing temperature they usually decrease, and with increasing pressure they increase. J. Amyx et al. [1, p. 291] believe that this proposition also holds true for oils. Others agree with them. Moreover, proceeding from this proposition, many authors—for example, V. S. Ugolev and V. I. Musinov [4]—propose heating the bottomhole of wells in order to increase inflow into them. Several types of installations have been developed for this purpose.

In order to determine the possibility of using this method to increase oil inflow into wells at the fields of Siberia, the petroleum-reservoir physics laboratory of the Tomsk Polytechnic Institute carried out a study of the viscosity of oil from the Klyuchevskoye field in Tomsk Oblast at various temperatures and pressures.

The study was conducted on the UINP-2M installation, equipped with a viscometer for studying oil viscosity at high pressures, VVDU-1, according to the procedure set forth by V. N. Mamuna et al. [3, pp. 90–94], and also by F. I. Kotyakhov [2, pp. 234–238].

The study showed that, with increasing pressure, the viscosity of the oil does in fact increase; however, this increase is not proportional. For example, at a temperature of 60°C, when the pressure was increased from 150 atm to 200 atm, i.e., by 33.3%, the viscosity of the oil increased from 0.4059 centipoise to 0.5118 centipoise, i.e., by 26%. With a further pressure increase, not only was the increase in viscosity no longer proportional to the pressure increase, but it followed an entirely different dependence on pressure. Namely, when it was increased from 200 to 252 atm (to reservoir pressure), i.e., by another 26%, the viscosity increased to 0.5121 centipoise, i.e., by only 5.9%. The viscosity increased in a similar way at other temperatures (Table 1).

The change in viscosity with changing temperature proved to be quite unexpected. Namely, instead of decreasing uniformly as the temperature rose, it first (when the temperature was increased from 20°C to 60°C) did indeed decrease, but then (when the temperature was increased to 78°C) rose sharply, exceeding the viscosity

at 20°C. This phenomenon was observed not at one pressure, but at three. Thus, at a pressure of 150 atm and a temperature of 20°C the viscosity of the oil was 0.6719 centipoise; upon heating to 60°C it decreased to 0.4059 centipoise, and with further heating (to 78°C) it increased to 0.8628 centipoise (Table 1). At a pressure of 200 atm, with the same

Table 1.

changes in temperature, it first decreased from 0.7175 to 0.5118 centipoise, and then increased to 0.8856 centipoise. Finally, at reservoir pressure (252 atm) and the same changes in temperature, it first decreased from 0.7208 to 0.5421 centipoise, and then increased to 0.8909 centipoise (Table 1).

To what has been said it should be added that under surface conditions, that is, after degassing of the oil, its viscosity increased several times and reached 4.8436 centipoise.

As is known, the reduction in oil viscosity under reservoir conditions is promoted by the associated gas dissolved in it. The increase in its viscosity when the temperature is raised from 60°C to 78°C at pressures from 150 to 252 atmospheres is apparently also connected with the solubility of the gas, which, as is known, decreases with increasing temperature.

From the material presented, the following practical conclusion follows. Heating of well bottoms is not advisable in every oil field. Cases are possible in which heating will be accompanied by an increase in oil viscosity and a decrease in its inflow into the well. Therefore, before introducing bottom-hole heating in a given field, it is necessary to study the nature of the change in oil viscosity at various temperatures and pressures. In particular, in developing the Klyuchevskoye oil field, bottom-hole heating should not be carried out, since at pressures above the saturation pressure the oil has the lowest viscosity at a temperature of 60°C, which is more than 30° lower than the reservoir temperature (92°C).

LITERATURE

1. J. Amyx, D. Bass, R. Whiting. Physics of Petroleum Reservoirs (trans. from English). Gostoptekhizdat, 1962.
2. F. I. Kotyakhov. Fundamentals of the Physics of Petroleum Reservoirs. Gostoptekhizdat, 1956.
3. V. N. Mamuna, G. F. Trebin, B. V. Ulyanovskii. Experimental Investigation of Reservoir Oils. GOSINTI, Moscow, 1960.
4. V. S. Ugolev, V. I. Musinov. Thermal Methods in Oil Production. Gostoptekhizdat, 1959.

ERRATA NOTED