Pumping with "slugs" of Produced Water and Crude Oil

[GHSME]

Hello, I have an application where we will be pumping from a separator at 3000bpd into a pipeline maintained at 200 psi by a back pressure valve at the end of the line (to prevent gas break out). The separator the pump suction is attached to, as well as the pipeline it is pumping in to, will have a nearly 1:1 mixture of Crude oil (0.75 SG) and Produced Water (1.05 SG). When looking at a centrifugal pump to handle this application, I am worried about how the pump could stay in one place on the curve and not create severe surging. When the pump is filled with oil it will operate at 200 psi, but when the 1.05 SG water enters the pump, the discharge pressure will need to increase to 280 psi to stay at the same spot on the curve at 3000bpd... There is no way a control valve could act quickly enough to handle this (unless the slugs are VERY large), and I doubt a VFD could either.

Due to the control difficulties I foresee, I am leaning toward a positive displacement pump. Am I missing something?

 

[LittleInch]

The crucial word here is "mixture".

What is the actual mixture and why do you think you will have varying slugs of pure liquid?

For sure a PD pump will pump a set flow and be less concerned about the actual fluid so long as you've sized the motor for 100% water.

How long is the distance from pump to pipeline?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

What kind of separator do you have there? 2 or 3 phase?

With a 2 phase, (you seem to have this type) you separate gas from oil/water; the gas goes to the gas pipeline and the oil/water mix goes to the pump, then to the oil/water flow line. The oil/water mixture typically remains emulsified and there is no slugging. Its all mixed up oil/water liquid of average density.

If you have a three phase seperator, you get gas, oil and water our as separate streams. Gas to pipeline, oil to pump and on to tanks, or to the oil pipeline. Water goes to slop tank, or wherever. There is no slugging of any outlet stream. You should not use a 3 phase seperator, if you are pumping to a oil & water flow line.

Select whatever type of pump you want with a discharge head based on the highest density you expect your emulsion will have. PD or centrifugal. Generally only consider VFD variable speed, if you expect variations of Flow rates by more than 30% for significant percentage of total operating time.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

You need to understand what your 50% water cut fluid looks like as it will vary between crude oils and also whether the fluid is an stable emulsion or can easily separate.

Below 30% WC, it is definitely Water in oil, and generally well mixed.

Over 60 to 70% it becomes oil in water and can separate a bit easier.

If the separator is large or the retention time long, then your fluid can separate and needs to be remixed. You might also get variations in the mix percentage over time if the inlet pipeline is longs and slugs high water cut, expecially on start up or shutdown.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

Something don't make sense. If you are going to get 280 psig versus 200 psig when pumping water at 1.05 versus oil at .75 then that means you are pumping from a separator at 0 psig. So you are pumping from a oil production separator at 0 psig? And you are producing a differential head with a centrifugal pump of 616 feet at 87.7 GPM? And if you really are at 0 psig in the separator why would you have to keep the pipeline at 200 psig as the vapor would have separated from the liquid at 0 psig so if you only keep a pressure of 10 to 20 psig in the pipeline then no more vapor would separate?

 

[georgeverghese]

So separator MAX operating pressure is less than 200psig ?
If this is the backpressure valve at end of line, where is the level control valve for this sep?
Do you have a PFD or PID which shows this setup and the facility downstream of this backpressure valve ?