How is gas condensate different from oil?
Surely even those farthest from the oil and gas sector have heard about the so-called. gas condensate. But at the same time, not even all oil workers know what it is and how it differs from oil.
For example, last year Novatek discovered a new field. The press release says the following:
NOVATEK announced the discovery of a new gas condensate field on the Gydan Peninsula. The field's recoverable natural gas reserves are estimated at 52 billion cubic meters. m, reserves of liquid hydrocarbons (gas condensate) – 2 million tons.
Unfortunately, few people can clearly say what gas condensate is. Even oil industry professionals can come up with such definitions that it makes your head spin. Some argue that it’s just light oil. Like if it’s 0.82 g/cm3 or lighter, it’s gas condensate.
Others focus on composition. If it is gas condensate, then it contains little paraffin deposits (asphalt-resinous and paraffin deposits). It also does not contain thiophene sulfur and isoprenoids. Still others focus on factional composition. If the liquid contains more than 12.5% saturated alkanes C5-C14 (pentane-tetradecane), then it is a gas condensate. And so on.
Only this is all wrong. The funny thing is that if you take these substances and analyze them under normal laboratory conditions, then… there will be no difference. Because oil and gas condensate themselves are very heterogeneous substances and can differ greatly from each other. Even if they are produced from the same well, provided that different formations are exploited. I don’t understand the essence of these disputes at all, because geology textbooks well describe retrograde phenomena, which lead to the appearance of gas condensate.
The difference between oil and gas lies in one thing – in what form they are in reservoir conditions.
Everything contained in the formation is called fluid. These are oil, gas and water + gas condensate. Oil, of course, is in a liquid state. If there is gas in the field, then under enormous pressure it dissolves in oil, completely or partially.
But there is another situation when oil dissolves in gas. To do this, three conditions must be met:
There is more gas in the reservoir than oil
Reservoir temperature 90-95 degrees
The pressure is not lower than 200-250 atmospheres (20-25 MPa).
And under such conditions, it is not gas that dissolves in oil, but, on the contrary, liquid oil turns into a gaseous aggregate state and dissolves in gas. This phenomenon is called retrograde (reverse) evaporation.
When production occurs, gas with oil dissolved in it rises out. Temperature and pressure drop, and oil dissolved in gas precipitates. This is the same gas condensate. The phenomenon itself is called retrograde (reverse) condensation.
So, the difference between oil and gas condensate lies in the phase state of liquid hydrocarbons (under normal conditions) in reservoir conditions. If under reservoir conditions a mixture of hydrocarbons is in a liquid state, it is oil. If it is dissolved in gas and is a gas under reservoir conditions, and returns to the liquid state when the pressure/temperature at the surface decreases, it is gas condensate.
Gas condensate is obtained from gas condensate deposits. The largest field of this type in the world is Urengoyskoye, which contains in its depths a stunning 1.2 billion tons of condensate. But, alas, it won’t be possible to get all of it.
The problem is that when the pressure drops during development, it falls out directly in the formation. The condensate that falls out is considered irretrievably lost. To avoid this, it is necessary to prevent a drop in reservoir pressure. The technology has long been known – this is cycling. It consists in the fact that gas is produced together with condensate, the liquid phase is separated from the resulting gas (topped), and dry gas is pumped back into the formation to increase the pressure above the cricondenbar (the highest pressure at which the liquid and gas phases are in a state of equilibrium).
Only this technology is not used in practice in our country, or anywhere else at all. There were pilot tests in Canada, which showed brilliant results, but then everything stalled. The reason is simple – it is very expensive. More expensive than the cost of condensate.
In reality, they try to exploit the field in such conditions that it maintains pressure above the beginning of the dew point (condensate pressure) for as long as possible.
An important characteristic of gas condensate deposits is the condensate-gas factor, which shows the content of raw condensate (cm3) in 1 m3 of separated gas. This figure can be from ten to seven hundred cubic centimeters.
In practice, a characteristic called the gas condensate factor is also used – this is the amount of gas (m3) from which 1 m3 of condensate is extracted. The value of the gas condensate factor varies for different fields from 1500 to 25,000 m3/m3.
Gas condensate is a light transparent liquid of different shades of yellow, with a pungent odor of hydrocarbons. The shade depends on the depth of extraction. From the overlying strata it is slightly yellow, sometimes almost colorless. And from the underlying ones it is dark, almost black, outwardly indistinguishable from oil. This can be explained simply – the higher the layer. the lower the pressure in it. Therefore, the lightest and lightest liquid hydrocarbons dissolve in gas. As pressure increases (as the depth of the formation decreases), denser hydrocarbons begin to dissolve, which give a dark color.
Condensate that is brought to the surface is called wet or unstable. It contains a lot of gas that is dissolved in it (alkanes of the methane-butane series). After some time, they evaporate and a stable condensate is obtained, which consists only of liquid hydrocarbons (from pentane and higher) that are liquid under standard conditions.
Gas condensate is a valuable resource. It contains little paraffin, so high-quality gasoline is produced from it, and it is also used by the chemical industry to produce aromatic hydrocarbons
Author: Sigurd Sigurdov
