RESOURCES OF C₂–C₄ GASES AND LIGHT HYDROCARBONS IN GAS AND GAS CONDENSATE OF THE LUGINETSKOYE FIELD

N. M. Smolyaninova, A. V. Kravtsov, V. A. Kuznetsova

(Presented by the scientific-methodological seminar of the KhTF)

The Luginetskoye natural-gas field is located in the territory of the Kargasok District of Tomsk Oblast.

The field is a gas-condensate field and has an oil rim.

According to preliminary data, the condensate factor (for raw condensate) is equal to 180–230 cm³/m³ of gas.

During the operation of such fields, the gas-condensate mixture from the well enters a separator, where at a certain pressure the gas is separated from the condensate. The separated dry gas (separation gas) enters the gas pipeline, while the unstable (raw) condensate is sent for stabilization (degassing).

Of great importance for determining the value and direction of utilization of associated products from natural-gas production is an assessment of the resources of hydrocarbon gases (C₂–C₄) and light hydrocarbons C₅ in it. These resources consist of hydrocarbons C₂–C₅ contained in the separation and degassing gases, as well as gases dissolved in the stable condensate.

The present work is devoted to determining the quantity and composition of light hydrocarbon components in the natural gas of the Luginetskoye gas-condensate field, which is highly promising for industrial development.

Samples of gas and raw condensate were taken at the pressure of maximum condensation (76 atm) and a temperature of 20°C during testing of well No. 151.

The sample in the container was subjected to stepwise degassing on the UIPN unit from a pressure of 76 atm to atmospheric pressure, with six stages distinguished: 76–40 atm, 40–20 atm, 20–16 atm, 16–10 atm, 10–6 atm, and 6–0 atm.

At each stage, the volume and composition of the released gas were determined, and on the basis of these data the total composition and yield of degassing gas were calculated for the total volume successively by stages.

Analyses of degassing gas and dry gas were carried out by the method of gas-liquid chromatography on GAKh-21 and KhL-4 chromatographs. Separation of nonhydrocarbon gases and methane was performed on CaX molecular sieves; hydrocarbons C₂–C₅ were separated on INZ-600 modified with Vaseline oil.

Helium was used as the carrier gas. The composition of gaseous hydrocarbons dissolved in the stable condensate was determined according to the method of VNII NP.

The results of the analyses (in wt. %) are given in Tables 1 and 2.

Table 1

Composition and yield of gas from stepwise degassing (as a percentage of the total volume) of gas condensate from the Luginetskoye field, wt. %

The data on the composition of the degassing gas (Table 1) show that the hydrocarbon composition of the gas in the first three stages changes very little. As the pressure is further reduced, the methane content in the gas decreases, while the content of heavy hydrocarbons ($\mathrm{C_2}$—$\mathrm{C_5}$) increases. The total degassing gas (upon gas liberation down to atmospheric pressure) contains 12.1% ethane, 16.9% propane, 11.1% butanes, and 4.4% pentanes.

Table 2

Composition of separation gas and gas dissolved in the stable condensate of the Luginetskoye field

In all, when 1 m³ of raw gas condensate is degassed, 102 m³ of gas is released; the most intensive gas liberation (40.4%) occurs in the last stage (when the pressure is reduced from 6 to 0 atm).

The gas dissolved in the stable condensate (yield relative to condensate: 21.1 wt. %) consists mainly of butanes (35.9%) and pentanes (53.7%).

It should be noted that the separated dry gas still contains a considerable amount of $\mathrm{C_2}$—$\mathrm{C_5}$ hydrocarbons, among which the share of ethane is 6.6%, propane 3.7%, butanes 2.6%, and pentanes 0.8%.

The data on the resources of light hydrocarbons \((\mathrm{C}_2—\mathrm{C}_5)\) in raw gas condensate, given in Table 3¹, show that their amount is very large and is 25.38 wt.%; of this, the \(\mathrm{C}_3—\mathrm{C}_4\) fraction accounts for 12.74%, and the \(\mathrm{C}_3—\mathrm{C}_5\) fraction for 23.44%.

Table 3

Resources of \(\mathrm{C}_1—\mathrm{C}_5\) hydrocarbons
in raw gas condensate
of the Luginetskoye field

With production in the region of more than 10 billion m³ of gas and about 1 million tons of raw condensate per year, the resources of \(\mathrm{C}_2—\mathrm{C}_5\) hydrocarbons will amount to 200–300 thousand tons. Such volumes of gas and condensate production predetermine the need for the use and processing of light hydrocarbons.

Conclusions

1. A study has been carried out of the composition of separation gases, degassing gases, and gases dissolved in degassed condensate from the Luginetskoye field.

2. The resources of hydrocarbons of the \(\mathrm{C}_2—\mathrm{C}_5\) composition in raw condensate have been determined; they amount to 25.38 wt. % calculated for raw condensate.

3. The necessity has been noted of using propane–pentane components as feedstock for petrochemistry.

1. Calculated on the basis of the data in Tables 1 and 2. ↩