On the Physical Properties of Oil from the Nikolskoye Field in Tomsk Oblast
Abstract Generated abstract
This paper reports laboratory measurements of reservoir oil from well R-1 in the Nikolskoye field, Tomsk Oblast, sampled from the Yu-1 bed at 2380 to 2400 m. Using standard reservoir-oil analysis methods, two samples were examined for saturation pressure, gas content, formation volume factor, density, compressibility, viscosity under varying pressure and temperature, stepwise degassing behavior, and associated gas composition. The oil showed low saturation pressure and gas content, a comparatively high formation volume factor, low viscosity under reservoir conditions, and physical properties broadly similar to oils from other Tomsk Oblast fields. Viscosity decreased smoothly with temperature and increased with pressure, while the main viscosity increase during degassing occurred between 30 atm and atmospheric pressure, and compressibility rose as pressure declined.
Full Text
On the Physical Properties of Oil from the Nikolskoye Field in Tomsk Oblast
G. N. Chertenkova
(Presented by Professor A. V. Aksarin)
The oil-bearing horizon at the Nikolskoye field is bed Ю-1 (Vasyugan Suite), which is represented by interbedding of sandstones, siltstones, and argillites. Among the sandstones the most varied types are encountered—from fine-grained to coarse-grained. The sandstones are firm and bedded. The oil pool of this field was penetrated by well R-1 in the interval 2380–2400 m.
For the study of the physical properties of reservoir oil from the well, two samples were taken. The study was carried out in the laboratory of oil-reservoir physics of the Tomsk Polytechnic Institute on
Table 1
Basic physical properties of reservoir oil from the Nikolskoye field
(well R-1, bed Ю-1, reservoir pressure 240.5 atm, reservoir temperature 86°C)
| Parameters | Units of measurement | First sample | Second sample | Mean value |
|---|---|---|---|---|
| Date of sampling | 7.04.71. | 7.04.71. | ||
| Perforation interval | m | 2380— —2400 |
2380— 2400— |
|
| Saturation pressure | ati | 59 | 58 | 58 |
| Oil compressibility coefficient | \(10^{-5}\) 1/at | 16,06 | 15,43 | 15,74 |
| Gas content, referred to unit volume | \(m^3/m^3\) | 50,50 | 51,30 | 50,90 |
| Gas content, referred to unit weight | \(m^3/t\) | 60,37 | 61,36 | 60,86 |
| Formation volume factor | 1,198 | 1,202 | 1,200 | |
| Shrinkage | % | 16,53 | 16,81 | 16,69 |
| Density of separated oil | g/cm³ | 0,836 | 0,836 | 0,836 |
| Density of reservoir oil | g/cm³ | 0,750 | 0,748 | 0,749 |
| Gas density | g/liter | 1,230 | 1,231 | 1,230 |
| Average coefficient of gas solubility | cm³/cm³·at | 0,847 | 0,884 | 0,865 |
| Viscosity of degassed oil under reservoir conditions | centipoises | 0,70 | — | 0,70 |
| Viscosity of separated oil under surface conditions | centipoises | 5,02 | 5,48 | 5,25 |
| Final separation pressure | mm Hg | 760 | 755 | |
| Final temperature | °C | 20°C | 20°C | |
| Date analysis completed | 26.04.71 | 10.05.71 |
on the UINPN-2M apparatus. The work was carried out according to the method described by V. N. Mamuna et al. [1].
The basic physical properties of the reservoir oil of the Nikolskoye field are given in Table 1. This oil is characterized by a relatively low saturation pressure of 58 atm and an equally low gas content—50.9 m³/m³. At the same time, its formation volume factor is comparatively high—1.200. The viscosity of the oil under reservoir conditions is 0.70 centipoise, and under surface conditions after degassing it is 5.25 centipoise. In its physical properties, the oil of the Nikolskoye field differs little from oils of other fields in Tomsk Oblast.
Some of these properties were studied in greater detail. This applies above all to oil viscosity. The viscosity was determined for the oil both in the non-degassed and in the partially degassed state. The study was carried out at several temperatures and pressures. The temperatures were the same in both cases, namely 20, 40, 60, and 86°C (reservoir temperature). As for the pressures, they were partly the same and partly different. Thus, both in the non-degassed and in the partially degassed states, the oil was studied at pressures of 240.5 atm (reservoir pressure) and 100 atm. In addition, in the non-degassed state the oil was studied at pressures of 200 atm and 150 atm, and in the partially degassed state at 50 atm. Degassing was carried out at a pressure of 30 atm.
The study established that with increasing temperature the viscosity of the oil from the Nikolskoye field decreases smoothly, while with increasing pressure it increases; moreover, at the same temperatures and pressures the viscosity of partially degassed oil differs little from the viscosity of non-degassed oil (Tables 2 and 3). Hence—
Table 2
Results of the study of the viscosity of oil of the first sample from the Nikolskoye field
(well R-1, Yu-1 bed) in the non-degassed state
| Pressure at which viscosity was determined, atm | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures |
|---|---|---|---|---|
| 20°C | 40°C | 60°C | 86°C (reservoir t) | |
| 240.5 | 1.48 | 1.05 | 0.88 | 0.70 |
| 200 | 1.43 | 1.02 | 0.76 | 0.68 |
| 150 | 1.34 | 0.99 | 0.74 | 0.66 |
| 100 | 1.26 | 0.85 | 0.73 | 0.64 |
Table 3
Results of the study of the viscosity of oil from the Nikolskoye field
(well R-1, Yu-1 bed, first sample) in the partially degassed state
| Degassing pressure, atm | Pressure at which viscosity was determined, atm | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures | Viscosity in centipoise at different temperatures and pressures |
|---|---|---|---|---|---|
| 20°C | 40°C | 60°C | 86°C | ||
| 30 | 240.5 | 1.26 | 1.14 | 0.92 | 0.73 |
| 30 | 100 | 1.17 | 1.01 | 0.80 | 0.70 |
| 30 | 50 | 1.11 | 0.92 | 0.78 | 0.69 |
Table 4
Results of stepwise degassing of the first oil sample from the Nikolskoye field (well R-1, reservoir Yu-1, perforation interval 2380–2400 m)
| Indicator | Pressure, ata | Temperature, °C | Quantity of gas in solution, m³/m³ | Quantity of free gas, m³/m³ | Gas solubility coefficient, m³/m³·atm | Gas density, g/L at p | Volume coefficient | Oil density, g/cm³ |
|---|---|---|---|---|---|---|---|---|
| Reservoir pressure | 241,5 | 86°C | 50,50 | 0,0 | — | — | 1,198 | 0,750 |
| Saturation pressure | 60 | 86°C | 50,50 | 0,0 | 0,842 | — | 1,240 | 0,727 |
| 1st stage | 41 | 86°C | 49,48 | 1,02 | 1,151 | 1,100 | 1,234 | 0,729 |
| 2nd stage | 33 | 86°C | 42,85 | 7,65 | 1,224 | 1,020 | 1,227 | 0,728 |
| 3rd stage | 21 | 86°C | 36,66 | 13,84 | 1,591 | 0,958 | 1,223 | 0,726 |
| 4th stage | 13 | 86°C | 30,05 | 20,45 | 2,003 | 0,943 | 1,217 | 0,724 |
| 5th stage | 8 | 86°C | 24,38 | 26,12 | 2,709 | 1,058 | 1,211 | 0,722 |
| 6th stage | 4 | 86°C | 13,27 | 37,23 | 2,211 | 1,180 | 1,153 | 0,725 |
| 7th stage | 1 | 86°C | 0,0 | 50,50 | — | 1,930 | 1,139 | 0,734 |
| 8th stage | 1 | 20°C | 0,0 | 50,50 | — | — | 1,000 | 0,836 |
Consequently, the principal increase in the viscosity of the oil occurs in the course of degassing it in the pressure interval from 30 ati to 1 ata.
Of interest are the changes in the coefficient of compressibility of the oil. It turns out that this parameter increases as the pressure decreases (Table 5).
Table 5
Coefficient of compressibility of oil from the Nikolskoye field at different pressures
| Pressure, ati | Value of compressibility coefficients, in \(1/\text{atm}\): first sample | Value of compressibility coefficients, in \(1/\text{atm}\): second sample |
|---|---|---|
| 240,5—120 | \(12,04 \cdot 10^{-5}\) | \(11,07 \cdot 10^{-5}\) |
| 120—100 | \(19,14 \cdot 10^{-5}\) | \(14,02 \cdot 10^{-5}\) |
| 100—80 | \(20,18 \cdot 10^{-5}\) | \(13,98 \cdot 10^{-5}\) |
| 80—60 | \(29,85 \cdot 10^{-5}\) | \(17,51 \cdot 10^{-5}\) |
| Average values in the interval 240,5—60 | \(16,06 \cdot 10^{-5}\) | \(15,43 \cdot 10^{-5}\) |
Below are also given the results of stepwise degassing of oil from the Nikolskoye field, though only for the first sample (Table 4). The results of stepwise degassing of the second sample are similar and therefore are not presented in the present article.
Some attention must be devoted to the composition of the associated gases of the oil from the Nikolskoye field. They differ little from the composition of associated gases of oils from other fields in Tomsk Oblast.
Table 6
Composition of the associated gas of oil from the Nikolskoye field
(well R-1, bed Yu-1)
| Name of gases | First sample, in volume percent | Second sample, in volume percent |
|---|---|---|
| Methane | 74,13 | 51,78 |
| Ethane | 7,53 | 8,79 |
| Propane | 8,55 | 13,43 |
| Butane | 3,76 | 11,41 |
| Pentane | 1,21 | 3,37 |
| Hexane | 0,70 | 1,25 |
| Heptane | 0,77 | 0,47 |
| Carbon dioxide | 1,32 | 1,15 |
| Hydrogen | — | — |
| Nitrogen | 2,03 | 8,35 |
In particular, methane is in first place here (more than 50 volume percent), propane is in second place (from 8,55 to 13,43 volume percent), and only in third place is ethane (from 7,53 to 8,79 volume percent). The proportion of butane is large. In the second sample its content even exceeds the content of ethane. The content of the remaining gases is insignificant (Table 6).
In its physical properties, the oil of the Nikolskoye field differs little from oils of other fields in Tomsk Oblast.
LITERATURE
- V. N. Mamuna, G. F. Trebin, B. V. Ulyaninsky. Experimental study of reservoir oils. GOSINTI, 1960.