Compressibility Factor and Formation Volume Factor of Oil from the Klyuchevskoye Field in Tomsk Oblast
Abstract Generated abstract
This paper reports laboratory determinations of the compressibility factor and formation volume factor of oil from the Klyuchevskoye field in Tomsk Oblast, using samples from well 61 in the Upper Jurassic Vasyugan suite at reservoir temperature. Measurements on a UNNP-2M apparatus show that oil compressibility increased progressively as pressure declined from 252 atmospheres toward the saturation pressure of 73 atmospheres, rising from an average of 15.27 to 45.18 times 0.00001 per atmosphere, with a total oil volume increase of about 3.8 percent. Degassing measurements gave gas factors of 69.38 and 67.77 cubic centimeters per gram for two samples, while the corresponding formation volume factors were 1.221 and 1.222.
Full Text
COMPRESSIBILITY FACTOR AND FORMATION VOLUME FACTOR OF OIL FROM THE KLYUCHEVSKOYE FIELD IN TOMSK REGION
G. I. CHERTENKOVA
(Presented by Professor A. V. Aksarin)
The oil compressibility factor indicates how much the volume of oil increases when the reservoir pressure is reduced by one atmosphere, until this pressure drops to the saturation pressure. Knowledge of this factor is necessary for estimating the elastic forces developed by the oil in the reservoir during its withdrawal at pressures above the saturation pressure. After the reservoir pressure falls below the saturation pressure, free gas begins to be released from the oil, which is accompanied by a decrease in the volume of the liquid phase, that is, of the oil itself. The latter quantity is determined by the oil formation volume factor.
The oil compressibility factor is the ratio of the change in its volume to the product of this entire volume and the pressure drop. The unit of measurement of the oil compressibility factor is a quantity inverse to pressure, called a unit per atmosphere.
By the oil formation volume factor, M. A. Zhdanov [1] means the ratio of the volume of reservoir oil (when it contains dissolved gas) to its volume under surface conditions, that is, after the associated gas has been released from it. This quantity is measured in fractions of unity.
Both of the named factors depend on the composition of the oil, the reservoir temperature, the reservoir pressure, and the amount of gas dissolved in the oil.
Determination of the compressibility factor of the oil from the Klyuchevskoye field in Tomsk Region was carried out in the laboratory of petroleum-reservoir physics of Tomsk Polytechnic Institute on the UNNP-2M apparatus according to the method of V. N. Mamun, G. F. Trebin, and B. V. Ulyanovsky [2, pp. 22—23, 67 et al.] on oil samples taken from well 61 from depths of 2468—2488 m, from the Vasyugan suite of Upper Jurassic age, at a temperature of 92°C.
As the pressure in the press of the apparatus was reduced, this factor steadily increased. However, while the pressure was far from the saturation pressure, this increase remained comparatively small;
Thus, within the range of 252–160 atmospheres it may be taken as equal to \(15,27 \cdot 0,00001\) units per atmosphere (Table 1). Then the compressibility coefficient began to increase to a greater degree and, in the interval of 160–120 atmospheres, reached \(20,23 \times 0,00001\) units per atmosphere, that is, it increased by 1,33 times.
Table 1
| Pressure intervals, atmospheres | Compressibility coefficient of oil from the Klyuchevskoye field for different samples taken from well 61 at a depth of 2468–2488 meters (Vasyugan suite), in \(0,00001\) units per atmosphere | Compressibility coefficient of oil from the Klyuchevskoye field for different samples taken from well 61 at a depth of 2468–2488 meters (Vasyugan suite), in \(0,00001\) units per atmosphere | Compressibility coefficient of oil from the Klyuchevskoye field for different samples taken from well 61 at a depth of 2468–2488 meters (Vasyugan suite), in \(0,00001\) units per atmosphere |
|---|---|---|---|
| Pressure intervals, atmospheres | Sample No. 1 (sampling date: October 23, 1968) | Sample No. 2 (sampling date: October 24, 1968) | Mean values |
| 252–160 | 14,78 | 15,76 | 15,27 |
| 160–120 | 19,66 | 20,80 | 20,23 |
| 120–80 | 31,30 | 32,54 | 31,92 |
| 80–73 | 45,56 | 44,80 | 45,18 |
Then this coefficient began to increase to an even greater degree and, in the pressure interval of 120–80 atmospheres, reached \(31,92 \times 0,00001\) units per atmosphere, that is, it increased by another 1,58 times, and in comparison with the initial value—by 2,08 times. When the pressure in the installation press was reduced by another 7 atmospheres—from 80 to 73 atmospheres (saturation pressure)—this coefficient increased to \(45,18 \times 0,00001\) units per atmosphere, that is, it increased by another 1,42 times, while its total increase amounted to 3,16 times.
The total increase in the volume of the oil samples when the pressure was reduced from reservoir pressure (252 atmospheres) to the saturation pressure (73 atmospheres) amounted to about 0,038 of the initial volume, or 3,8%. As for the differences in the values of these coefficients in the study of different samples, they did not exceed \(1,2 \cdot 0,00001\) units per atmosphere in absolute terms (Table 1), or 6% of the values of the measured quantities.
The determination of the volume factors was also carried out according to the method of V. N. Mamuna et al. [2] and consisted in measuring the volume of an oil sample first under reservoir conditions (that is, in the presence of dissolved gas in it, at a pressure of 252 atmospheres and a temperature of 92°C); then the oil was degassed and the volume of the same sample was measured under surface conditions. During the degassing of the oil, the quantity of gas liberated from it was determined, and from this—the content of gas per gram of degassed oil, that is, the gas factor.
The gas factor for the first sample proved to be 69,38 cubic centimeters per gram, and for the second—67,77 cubic centimeters per gram, while the volume factors were 1,221 for the first sample and 1,222 for the second.
REFERENCES
- M. A. Zhdanov. Oil-and-Gas Field Geology. Gostoptekhizdat, 1962.
- V. N. Mamuna, G. F. Trebin, B. V. Ulyanovskii. Experimental Study of Reservoir Oils. GOSINTI, 1960.