Produced Water Backpressure
Produced Water Backpressure
(OP)
Afternoon all,
Having a discussion offshore around a produced watere overboard line.
We have our overboard line submerged in water up to a depth of 20m. We are wanting to extend the overboard line to 40m below the sea surface.
Therefore I would imagine that we would have a greater back pressure on the system as we would have to displace 20m more of submerged pipework to allow our water to be removed.
Am I correct in what I am saying?
Having a discussion offshore around a produced watere overboard line.
We have our overboard line submerged in water up to a depth of 20m. We are wanting to extend the overboard line to 40m below the sea surface.
Therefore I would imagine that we would have a greater back pressure on the system as we would have to displace 20m more of submerged pipework to allow our water to be removed.
Am I correct in what I am saying?





RE: Produced Water Backpressure
RE: Produced Water Backpressure
Biggest problem with putting the pipe 40 m under the water is supporting and stabilizing the pipe.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Produced Water Backpressure
RE: Produced Water Backpressure
I guess you could let the system back up or "stack up" as was mentioned above and discharge the water in slugs. But now your discharge is going to be cyclical. Water backs up...discharges. Water backs up... discharges.
RE: Produced Water Backpressure
Surely if we have an extra head of liquid in the pipe then the force required to displace has doubled.
RE: Produced Water Backpressure
Have either of you seen a manometer? If I add liquid to one leg, the level reaches a new equilibrium height, but the surface pressure doesn't change and the length of the leg is immaterial. In the case mentioned, one leg of a manometer is the pipe and the other leg is the whole ocean. As long as the fluid is predominantly liquid, the depth is immaterial.
If your dump hung open and you blew gas into the pipe, you would have to blow at a higher pressure to break the seal with 200 m of pipe than 40 m of pipe, but as long as the pipe has liquid in it, depth doesn't matter.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Produced Water Backpressure
Good luck,
Latexman
RE: Produced Water Backpressure
RE: Produced Water Backpressure
Now as that tank begins to fill the tank nozzle becomes submerged. Now the nozzle is 1 ft below the surface of the liquid. What is the back pressure on the system? One ft of liquid. As the level builds the back pressure increases. Do you not agree with this?
Up, down, sideways, inside out. If that pipe is submerged 40 m the back pressure on the other end is 40 m.
RE: Produced Water Backpressure
Now put the pump on a 200 m hill and everything I said above is still true, except it remains true until you've filled the tank above 190 m.
I live in the Rockies, and I promise that pumping uphill is a very different situation than pumping downhill.
David
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Produced Water Backpressure
So lets say we have two tanks, both at the same elevation. Tank A is filled to the 50 ft mark, Tank B is empty. A line connects the two. You open a valve so that Tank A can flow into Tank B. Where does the level end up? They settle out at 25 ft, right? In order to increase the level in B and decrease the level in A I would need an additional pressure source.
So lets look at the submerged pipe. At the water surface the pressure is atmospheric. The pressure at the bottom of that pipe is density x gravity x height. So at 20 m, the pressure at the pipe outlet is 20 m of water. If the pipe is submerged 40 m, the pressure at the pipe outlet is 40 m of water.
Just like a sump pump. If you were to calculate the suction pressure available at the impeller would you not say it was the the height of liquid above the pump?
If I have a fractionator column where the overhead flows to an overhead accumulator that has a submerged dip pipe. I can manipulate the pressure in my fractionator by adjusting the level in my overhead accumulator.
RE: Produced Water Backpressure
In that case, when you finally have air coming out the bottom, you have a water column of 40m versus an air column of 40m and because of the density differences, you need additional air pressure. However, with water, the column (and pressure) caused by the 40m length is the same as the column (and pressure) of the water outside of the pipe.
RE: Produced Water Backpressure
I get it now. Geez...sometimes I can be dense. Even though you are submerging the pipe an additional 20 m you are gaining the same 20 m in static head. There is no change in back pressure - assuming the produced water and sea water have the same specific gravity that is.
I am man enough to admit I was wrong and you guys were right. :)
RE: Produced Water Backpressure
RE: Produced Water Backpressure
Best regards
Morten Andersen
RE: Produced Water Backpressure
David
RE: Produced Water Backpressure
RE: Produced Water Backpressure
That is BRILLIANT advice!!!!
I wish I had said that. Hey . . . wait a minute . . . I did!
Good luck,
Latexman