Pipeline Back pressure issue 3

[Osm.abdo]

Hi All
we have 12” pipeline , 44km long at 75c exporting temp the initial production is 10000 BOPD, (70m3/hr). now the production decline to 2000 BOPD which has raised flow assurance risks in view of the low flow (pipeline minimum flow rate) which associated with the crude gelling (pp =36c) .
The landing temp is 35-36C and now we face back-pressure due to crude gelling . so my question is adding screw pump (low capacity, high pressure) to increase the pressure will solve the back pressure issue or not ? Knowing the fact that, pipeline can stand 100 barg although installed piping on pipeline is designed to 600#.
also if there any other solutions or mitigation measures can be used please share it.
Thanks in advance.

 

[MortenA]

Have you checked you pp recently? It may change over time and this could be lower Also there are several ways of determining this value. Som includes "thermal history" some dosnt. This may give a much lower PP. These are "design issues" so if your operation shows you that you do have PP issues this is irrelevant. But if you havnt had problems before you may be in a better position than you think.

Apart from this you can use a PP depressant - but that will add OPEX at a time when you dont need that! You dont want to operate below PP but i think you will have some margin. Another issue will be restart after a longer shut down - but i assume you already have had that experience?

Best regards, Morten

 

[Osm.abdo]

Thanks MortenA for your reply actually we checked the PP recently and as you said it was changed from 33 to 36. and as you said using PP depressant is not economically feasible with the current low production and high OPEX so we try to find another less cost and permanent solution for this back pressure issue.
yes we have the experience of restart operation.
thanks again.

 

[LittleInch]

There are many ways of dealing with this, but all cost money and have some negative issues

First data
You state the pipeline is good for 100 bar but then refer to some presumably ASME class 600 piping which should be rated for close to 100 bar. If you list steel grade and wall thickness we can quickly check that.

Options
1) Yes raise pressure to combat the increased viscosity of the oil, but there is a limit to this (i.e. 100 bar)
2) Increase initial temperature
3) dig up the pipe and insulate it ( probably not practical)
4) install a heater station half way along
5) pump in PP depressant (if it works - it is very dependent on specific crudes)
6) Run it as post inversion ( oil in water so ~ 70% water cut) then separate again at the far end
7) Batch it with hot water to increase overall flow rate.
8) Inject some sort of diluent ( kerosene or similar) but you might need quite a lot
9) Option from 7 is build up a line fill(or maybe less) of Crude (23,000 bbls) pump that in then flush with water or diesel for the entire line fill, then when you're ready flush that line fill back, pump your crude then flush it again. Gets over the going solid if you let it sit there issue but you do start to need a lot of tanks and pumps.
10) Start trucking it. 2,000 bopd is about 15 trucks a day.

Up to you.

Let us know what you think / finally do.

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

 

[Osm.abdo]

Thanks LittleInch
yes pipeline rated to 100 bar and now the operating pressure is only 10 bar, the ten options you stated we already sort it and i will state our point of view for each one as follow:
1) Yes raise pressure to combat the increased viscosity of the pipe (1st ranking option we studying it now)
2) Increase initial temperature (already heat the crude at initial to the maximum)
3) dig up the pipe and insulate it ( probably not practical) - agree with you
4) install a heater station half way along (2nd ranking option under study)
5) pump in PP depressant (if it works - it is very dependent on specific crudes) (economically not feasible)
6) Run it as post inversion ( oil in water so ~ 70% water cut) then separate again at the far end (end user is refinery required 0.5 % WC)
7) Batch it with hot water to increase overall flow rate. ((end user is refinery required 0.5 % WC))
8) Inject some sort of diluent ( kerosene or similar) but you might need quite a lot (we have shortage in products its NA)
9) Option from 7 is build up a line fill(or maybe less) of Crude (23,000 bbls) pump that in then flush with water or diesel for the entire line fill, then when you're ready flush that line fill back, pump your crude then flush it again. Gets over the going solid if you let it sit there issue but you do start to need a lot of tanks and pumps. (need high capex compared to option 1)
10) Start trucking it. 2,000 bopd is about 15 trucks a day. (last option if we can't find way to benefit from pipeline property)

really thanks for your informative reply. i will back to you with what we conclude at final. now there is engineering firm doing the FA study.

 

[LittleInch]

One thing not mentioned here is what the waxing issue is. If you have high PP Crude then wax normally rears its head as well. This could end up being your biggest issue.

With FA there is the issue of heating up the surrounding soil which is difficult to get right in many programs.

The effect can be quite high but there is an issue when you start to slow down in that the temperature decreases and hence viscosity increases and then flow slows down....

But batching with water can be used with a minor loss into an interface tank, especially if you use pigs and you still end up with Crude with a low WC.

Its an easy way to increase flowrate and increase arrival temperature but you do need some tanks at both ends and of course a supply of water...

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

 

[Osm.abdo]

its light crude so the main reason for back pressure is gelling but you are right waxing issue is also factor that we need to considered in FA, actually we don't find software simulating the gelling issues. batching with water is an option but the pipeline designed to handle processed crude so may lead to corrosion and damage the pipeline.
From the first screening of options we propose increase the pressure by screw pump so we need more information is it possible to flow the crude or we will face blockage (advantages and disadvantage of increasing pressure to overcome the back pressure)

 

[LittleInch]

As you get close to the pour point the viscosity starts to rapidly climb (X 1000). Some packages just can't deal with this and it needs specialist software and experienced engineers to replicate this.

Your issue is really what happens as the flow slows even more or stops for a while. You can quite easily get to a point where you just can't shift the stuff regardless of how much pressure you add. That might only be a fall of 2-3 C.

There's generally no easy or cheap solution to this.

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

 

[quadtracker]

More frequent pipeline pigging might help keep the lines clear of wax and solids (sand or asphaltenes). There could be build up in low lying areas such as valleys. Perhaps batching some chemical in front of the scraper pig to help to clear the line. There must be a chemical company that has that experience and technology. There are various types and shapes of pigs available. Batching diluent would be preferred in front of the pig. Once the line is clear pigging maybe all you need.

 

[quadtracker]

It looks like you have lost about 80% of your production and if your pumps are in good condition your in trouble with your pipeline you could lose your pipeline. Your first pig should have a locator tag so that you can find it if it gets stuck in the line. If that happens you will likely need to dig up the line and replace that pugged section of line. Its a long line maybe install pigging facilities at that point. I would be surprised if there is an easier solution.

 

[Osm.abdo]

Yes you are right there is no an easy solution to overcome this issue and now its under study to evaluate the options stated above or to start trucking. thanks for your valuable comments .

 

[georgeverghese]

Run some lab experiments to see if you can develop your own pour point depressant - most of the highly priced commercial PPDs' are some kind of ketone in a diesel diluent - see if any of the following ( or other similar) works for you:
Methly ethyl ketone (MEK)
Methyl isobutyl ketone ( MIBK)
Methyl isopropyl ketone

These are commonly used for lube oil dewaxing in refineries. Will be a whole cheaper if you can source these chemicals from the open market.

Else option 4 on @LI's list sounds practical. Guess laying another smaller electrically heat traced and insulated pipeline is out of the question but you could include it on the list, especially if you already have corrosion issues with this existing 12inch line.

 

[GD2]

osm.abdo,

Do you have process engineers in your company?
Why don't you let them run a heat and mass balance and give you the new crude characteristics along the 44 km pipeline? Try adding an online heater at the pumping end and see the characteristics again.

Once you get the new fluid properties, you can shop for pumps.

GDD
Canada

 

[itsmoked]

Can you pull a smaller line thru the existing line? The power company did that here with a lot of their gas lines and mains. Went from steel to plastic.

Keith Cress
kcress -

http://www.flaminsystems.com