Subsea Launcher/ Bi-Directional Pigging

[suraiya]

I'm currently working on an oil and gas subsea project whereby the client plans to tie-back a two-well marginal field (to a common manifold, and then) to their host facility, which is some 8 miles away.

As part of the given operating philosophy, they'd like to have the pipeline piggable. The easiest way, in my opinion is to construct a dual-flowline loop that will allow the pig to be deployed roundtrip.

Think of it again, I doubt that this will be the most optimized solution from economic perspective, given that this is a marginal field project. Two alternatives that come to my mind is bi-directional pigging and subsea launcher system. My concern, however, is on the operability of these options (and the inherent difficulties)

Is anyone in this forum with experience in such application, who could share their thought?

 

[BigInch]

The only problem for bidirectional pigging is turning the flow around and finding the room for building the liquid, wax & crud handling tanks and drain systems etc. on each end. If you can do that, there is no need for 2 pipelines, so you've just saved somewhere around 5 to 10 million dollars. If you like, you can send me 10% of the savings for that little pearl of advice.

You can easily make launchers and receivers that will operate in both capacities. Attend to the proper placements of drains and kicker lines.

You should try to eliminate any changes in line diameter between the launchers/receivers and, of course, NO CHECK VALVES between the launchers. If you need check valves in other locations, a bypass around those will be needed. Otherwise the usual pigging pipeline design requirements can be followed (no protrusions, orifices, other restrictions, into the line, etc.). If you have two phase flow, pay attention to the slopes and possible liquid holdups in each direction and resulting volumes of possible slugs, ie, do a bidirectional hydraulic analysis.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[zdas04]

Is the reason you want this thing bi-directional so that a person does not have to go to the satelite platform to load the pig? If so then you don't really need a launcher at all. Load the pig in the receiver, push it back to the remote site with high-pressure fluids and then put the wells back on (this can just be a check valve upstream of the place you want the pig to stop). One problem with this is that you will be packing any accumulated solids into the normal flow line and can create a bigger problem than you're solving.

I'm thinking that a loop of smaller pipe makes more sense from an operating standpoint. Just bring the satelite into the loop with a check valve and then you can cycle the pig out and back from the production platform. With bad wax problems this is probably your only way.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[BigInch]

Only three things don't fit.

1. Marginal,
2. Subsea launch/Receiver, and
3. 2 flow lines.
-------------------
Think about it. Its not that hard.

2 wells to
One manifold
One line
One way
Minimum Investment
Minimal Risk
Minimal Op difficulty
Minimum Maintenance
Minimum Ondeck facilities




BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[SJones]

You only have to Google to see that Statoil and BP are using subsea launchers. As to their operating costs and reliability, that would have to be factored into the life cycle cost evaluation of the configuration options that you have on the table.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[BigInch]

No question that the equipment exists. Also no question that the equipment is expensive and therefore its utility for a field described as "marginal" is improbable. Its also true I don't even know the water depth, so not too much else I really want to say about it.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[suraiya]

Really appreciate all the responses.

Indeed, the keyword here is "marginal", i.e. how to deliver the most optimized two-well subsea project from life cycle cost point of view. Obviously when talking about life-cycle-cost, critirea such as operability, maintainability, reliability etc are factored as part of items that build up the OPEX and CAPEX.

I guess bi-directional pigging will be the cheapest option from CAPEX. The issues here are (1)they are not 'intelligent' (2) I'll need to shutdown the system for pigging (since in most likelihood I'll launch from the host platform, which is counter-flow direction).

Unless if I launch from the subsea source. But then again
I'd need a subsea launcher in that case. And if I 've a subsea launcher, why would I need bi-di pig. That'd be overkill.

So the issue now is which one will be a technically acceptable option, and commercially lowest from life cycle cost perspective.

 

[BigInch]

Not shut down, reverse.

Will you force the liquid/crud back down into the well, or will you have somewhere else to put it? I'm not understanding that aspect. 8 miles of pipe is a lot of liquid to back into the well? Actually its a lot of liquid to put anywhwere.

Is there another solution to pigging? Can you insulate the lines, heat the line.... with a bundled circulation line. What exactly are you getting out of that well that's causing the problem, hi wax, sand, hydrates, all the above?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[SJones]

The word 'intelligent' has also popped up with respect to pigging. That would start a whole new ball game.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[suraiya]

BigInch,

Apology for not being clear enough. It is a gas field with high condensate ratio, also with potentially corrosive fluid.

Apart from slugging (which is not that bad actually), the client wanted some means to assess the pipeline integrity from time to time- e.g. wall thickness losses and what not due to corrosion.

 

[zdas04]

That's like saying "I really want a compact car, and by the way it must occasionally pull a 100,000 kg trailer over the Alps". Allowing for smart pigs is not a small undertaking.

You really need to get all of your requirements clearly defined before you start your design. In your original post you talked about removing parrifin which would be a major problem for running any pig towards the wells (the pig will tend to push the wax in front of it and pack off the well-end of the pipe and seriously stick the pig). Any pipeline problem can be solved through proper materials, sound engineering, and ingenuity--it just takes money.

David

 

[BigInch]

There are corrosion monitoring coupons, or even electronic corrosion monitors that just take a weldolet and a wire or two to install. I would think you could economically handle corrosion loss in this situation by giving the wall thickness a greater allowance to compensate in advance for the estimated loss. If its a marginal field, it doesn't sound like the life will be too terribly long to worry about it chewing it up. If it was to be a 50 yr life pipeline, that's another story.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[DrillerNic]

Speaking to someone I know at GD Engineering, who make pig traps, he says their subsea pig launcher is deployed, with pigs installed, from the surface off a DSV. So if necessary, could you simply the design the line to be pigable, and design the subsea manifold to be able to accept a subsea pig (ie a couple of wet connectors, a flow loop and a couple of valves to divert flow at the manifold through the launcher), and leave the actual purchase/ hire of the launcher to a later date if pigging becomes necessary...ie if their corrosion monitoring at the reciving host suggests a problem in the line at a later date?

 

[DrillerNic]

Also, I wouldn't like to try and bullhead 8 miles of fluid back into a well, so the bi-di pigging idea will give the the Well Engineers heart failure!

 

[SJones]

A subsea field signature monitor (FSM) for corrosion monitoring may be the maximum capex you would wish to go to on the integrity front unless the fluids will pose a major HSE/reputation/financial risk if a loss of containment occurs. So, if pigging is not required for flow assurance; and pipe cleaning prior to intelligent pigging is considered redundant, does the problem go away?

Some detailed work on predicting internal corrosion rates would also help your cause.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[suraiya]

Thanks DrillerNic.

Another option that I'm considering is to have automated subsea launcher, where you slot in couple of pigs into the launcher (you need longer traps, and some sort of valves or barrier between each pig, of course,and release one at each desirable time, using timer, or remote control from the host).

I'd try to avoid using DSV, as it tends to be more expensive (the diver rates is exorbitant!!), and poses more safety risk. As much as possible I'd go with an ROV.

I do agree with Steve, that alternative to Intelligent Pigging, such as FSM should be exp[lored as well. Will propose this to my client.

Thank you.