As simple as the O&G industry is often portrayed, in reality, it’s quite an elaborate and sophisticated process. With multiple stages involved and macro and micro levels, the process can be broken down into drilling, extraction, production, and refining, among others.
Separation of oil and gas is common in wells where natural gas and crude oil are found in the same wells. Since water, oil, gas, and other liquids have different density levels so the mixture can lead to problems down the road.
Oil is much denser than water, with gas being even less dense than crude oil. Therefore, separators are incredibly common in oil and gas extraction and production facilities. They’re also known as slug catchers, scrubbers, centrifuges, FWKOs, and more.
Companies in the oil and gas sector use different pieces of equipment to separate fluids from oil and gas physically, not chemically. Gravitational separation utilizes material differences to separate different products found in a single stream into diverse streams, each of which is distinct from the other.
However, depending on the well’s fluids’ properties and the required task at hand, some principles govern separation. While there are seven principles, only one principle may be used sometimes. In other situations, it may be more expedient to use more principles to get desired results within a set timeframe.
Principles of Oil and Gas Separation
#1- Pressure Change
As one of the most essential principles of oil and gas separation, the pressure change that separates light oil from heavy one might be different. However, there will always be a certain degree of pressure change involved when separating components of any mixture.
Depending on the task at hand, pressure on vessels containing hydrocarbon can be manipulated to enhance the process of separation. When the steam pressure in the vessels containing hydrocarbons decreases, the lighter hydrocarbons flash from the liquid stage into vapor form.
In contrast, if the vapor pressure in the hydrocarbon-containing vessels increases, the lighter hydrocarbons would condense from the steam phase back into the liquid state. But the principle only remains effective if the temperature remains constant.
#2- Temperature Change
Differences in fluid temperatures impact their relative volatility when vapor pressure levels and solubility alter and effects their compositions equilibrium during separation. Heavy oils accumulate near the water or oil emulsion when the temperature increases since they have a lower vapor pressure and higher viscosity than light oils at a certain temperature. This results in enhanced separation efficiency as compared to operating when temperatures are low, and there’s more volatility in both phases.
Temperature changes go hand-in-hand with changes in pressure when it comes to separation in vessels containing hydrocarbons. If the pressure remains constant, an increase in temperature can cause some of the lighter hydrocarbons to flash from the liquid to the vapor phase. Similarly, a temperature drop at fixed pressure causes the hydrocarbons to condense into a liquid phase.
The difference in the specific gravity of all the components being separated is a crucial factor that impacts the time it takes for the components to separate properly. The greater the difference, the faster the separation will be.
The difference between the specific gravity of oil, water, and gas is significant. Therefore, gas doesn’t take as long to break out and rises to the top of the liquids quickly.
When the difference between specific gravity is less, it implies more retention or settling time for the components. And if the difference is greater, gross separation would take place quickly.
#4- Scrubbing Action
Scrubbing is the action that segregates gas from oil. The stripping action determines the number of various physical phases required to remove the oil. Pressure, viscosity, density, and temperature are properties that are useful for determining the processes that are likely to yield the most efficient separation.
#5- Chemical Action
The interfacial area between two immiscible liquids should be retained for a successful separation with chemical action. A dip in temperature would always eliminate or reduce three-phase contact, which results in lower separation efficiency. This means that pressure has an inverse impact on the separation efficiency.
When the pressure decreases, the relative separation velocity increases, which results in increased efficiency, and vice versa. Agitation change speed variation changes the contacting zone’s width, which could impact separation efficiency negatively or positively, depending on the varying conditions.
This fundamental is based on the fact that water and oil have different dielectric constants. So, when the water and oil mixture is electrically grounded, one phase will have a positive charge while the other will have a negative charge, causing the two to separate. The method is commonly employed in horizontal as well as vertical vessels.
#7- Retention time
Hydrocarbons’ retention time in the separator can be useful for determining the amount of gas that can be recovered. The more the retention time, the greater the oil can be removed. That’s because the oil will not rise as long as it remains in contact with inert gas. The longer the contact time between the liquid and inert gas, the more the amount of oil will dissolve into the vapor stage.
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