Oil-water separation
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Secondary separation is mostly used for crude oil with a high relative density; tertiary separation is generally used for crude oil with a medium relative density; fourth-stage separation is typically used for crude oil with a low relative density. May I ask if what has been mentioned above is correct? Why?
The principles of oil-water separation include gravity separation, coalescence separation, filtration, and adsorption. Different separation processes can be designed using various methods.
I’m confused – what exactly do you want to do? The separation stage is related to the inlet pressure and the dehydration performance of crude oil. Generally, high-pressure wells (above 8 MPa) employ three-stage or four-stage separation, while others use two-stage or three-stage separation.
Secondary separation is mostly used for crude oil with a high relative density; tertiary separation is generally used for crude oil with a moderate relative density; fourth-stage separation is typically used for crude oil with a low relative density. This is what I found in relevant materials, and I don’t understand why crude oil with a lower relative density requires more stages of separation ?
Those with a low relative density exhibit a large density difference between oil and water; therefore, the head pressure of the oil-water mixture can be utilized multiple times for centrifugal separation of oil and water (the residence time for each separation is short, and most of the water separated out is free water)； Crude oil has a high density, and the difference between oil and water is not significant; therefore, it is difficult to separate them. Two stages are sufficient – using an additional stage will not result in much more water being separated, which would be a waste. Of course, this is on the condition that the well pressure is high enough, with a certain head pressure still remaining at levels 3 or 4. It’s just my personal opinion; professionals need to verify it.
The number of stages for oil-water separation has little to do with the density of crude oil. In domestic oil fields, one stage of gravity separation, followed by two stages of electrical dehydration or thermochemical dehydration, is generally sufficient to meet the requirements for the crude oil to be exported. What the original poster mentioned might be used in high-pressure wellheads, but it is not determined by the magnitude of the density difference.
Generally, oil wells have a maximum of two stages of separation; few ones in China use three stages of separation.
I have also done high-pressure work, but only up to level 3; I’m not sure about level 4