Design of Gas Gathering Systems 4

[ChEMatt]

Hoping this is the right forum, as there is the pipelines, piping, and fluid mechanics forum, and the gas distribution engineering forum (which doesn't look well traveled) as well.

I have experience with compressors, compressor stations, and pigging station design, but I have no experience with the design of gas gathering systems. I see a course by Petroskills that would be perfect, but my employer would not pay for such a course (not employed by a midstream company at the moment).

So I'm here asking for references to educational resources on the design of gas gathering systems. I understand that the actual pipeline sizing would be handled by any one of a number of pipeline simulators. What I'm looking for more is guidelines on routing and layout, construction, pressure testing, pigging considerations (I have built one pigging station in my lifetime; I would not consider myself to be a pigging expert but am familiar) API/ASME/etc. codes, rules of thumb, and, well, anything else I haven't mentioned here related to building and optimizing a gathering system.

I spent about 18 months in the midstream business and built three compressor stations so I'm familiar with the concepts involved in designing slug catchers, compressor station layout and utilities, CFR part 192, etc. I just don't know much about the gathering/pipelining side of it.

I appreciate whatever guidance you all can provide. Thanks!

Onwards,

Matt

 

[zdas04]

EmmanuelTop,
Yes, there is a very good way around the problem--make the line piggable (for 6-inch and smaller lines I use an Argus Pigging Valve (watch the video at the bottom of the page). These valves do not fit in the space of an API 6D ball valve, but they are well worth the effort to cut off flanges and reweld them. For bigger lines you need to suck it up and install full blown pigging facilities. Pigging is the only answer to the problem. Big lines accumulate condensation. Small lines waste horsepower. I always go for bigger lines and pigging.

BigInch,
When that pipe was being developed in the 80's the called it "Spoolable Composite" pipe. This stuff is really cool. Comes on long spools (one manufacturer puts 1500 m of 3-inch on a spool), and most of the good ones have some sort of hydraulic crimp for fittings (much like you use on PEX in your home). Some of the original brands used a sheet and resin process to seal fittings (think of building a boat in your garage) and the field hands truly hated it.

There are several really good manufacturers.
[ul]
[li]FiberSpar is the biggest by a long ways. Their adds say they've installed over 7 million miles of pipe. You have to watch them because the developers have no feel for Oil & Gas. They state their sizes in terms of OD, so a 6-inch pipe is just over 5 inch ID. They have a new 6.5 product that has an ID that is similar to steel 6-inch. I like FiberSpar, I've used it on a couple of jobs[/li]
[li]FlexSteel was developed for offshore and it is the only spoolable composite that approaches neutral buoyancy in water (the strength layer is actually steel). It is a bit higher price than FiberSpar, but they are really easy to work with and I've specified FlexSteel for a project I'm doing in Southern Africa (Kalahari Desert) next year.[/li]
[li]Soluforce is kind of the new kid on the block. A friend of mine just did several significant jobs with it in the Rockies and he loves it (he is a field guy who has installed every sort of pipe that has ever been sold).[/li]
[/ul]

If you haven't ever used this stuff you won't believe the results. I typically budget 40% for material and 60% for labor on steel jobs. I just did a post appraisal on two HDPE stick jobs (one in India and one in Australia) and both of them were 20% material and 80% labor. The last spoolable composite job I did was 88% material and 12% labor. Since the stuff cost about the same as steel the savings is huge (Steel jobs are running about $1500/in-mile, and the SC job I did was $700/in-mile) because you don't need welders or ditches (you can plough this stuff in like buried cable). FiberSpar reported one job where they were averaging 1 mile an hour from mobilization to flowing gas.

David Simpson, PE
MuleShoe Engineering

"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.

 

[BigInch]

Yes David. Soluforce is the one they were installing in LA. Download their catalogue.

You've put up the links, so I'll post the Canadian Asso of Petroleum Producer's report.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[SJones]

Pipelife in The Netherlands is an RTP supplier I have used. There was 200+ km of the stuff in Oman at the time. I'm also keen on GRP and have used that up to 120 bar in flowline systems. Both have the advantage of not corroding from the outside, so half the corrosion battle is won already. Unfortunately, it does mean that designers and installers have to be totally experienced with the materials. Can you picture the Good Ol' Boys of David's stories trying to get to grips with that 'durned plastic?' API 15S is the spec for RTP; ISO 14692 for GRP.

With acid gas corrosion typically being a mass transport phenomenon, general CO2 corrosion rates tend to increase with velocity. Erosion in a liquid containing system tends not be as severe as a gaseous system with solids since the liquid film cushions the particle impact. Both aspects can be modelled with some off the shelf tools to get a feel, but don't descend into 'turd polishing' on the modelling front! You can't model MIC corrosion rates anyway, however, a lot of people would say that you have to be doing something pretty wrong to get MIC in a gas system, particularly if MEG has to be used for hydrate control.

Utility pigging is an ace tool for corrosion control in wet gas pipelines. So, if you have made the system piggable, and have the will to use pigs, it's a great start.

http://www.capp.ca/library/publications/industryOperations/pages/pubInfo.aspx?DocId=155645

http://www.capp.ca/library/publications/industryOperations/pages/pubInfo.aspx?DocId=155644

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[zdas04]

BigInch,
I'm not going to thank you for posting that link. Whatever idiot decided it was a good idea to intermix stick FRP piping with spoolable composite and then not clearly say where something was important to FRP but not to Spoolable products needs to never have access to Microsoft Word again. 3/4 of the document was warning of the dangers of stick FRP and it is really hard to dig that out of the verbage.

SJones,
Those Good Ol' Boys have laid many thousands of miles of every kind of pipe marketed, they successfully laid FuturePipe in winter in the Rockies (that is the one with the sheet and resin, must be installed above 60F and the resin has an open time of under 15 minutes), I wouldn't discount their ability to install any pipe.

As to hydrate inhibition, that is not part of my world. The minimum clathrate-formation pressure for methane is about 400 psig. Mostly I'm working with reservoir pressures less than half that. No one is using large quantities of bulk methonal in low pressure gathering, and I strongly discourage it in higher pressure lines (ever read the MSDS on that stuff, I'd rather the guys were using Agent Orange).

I've tested several hundred samples of water (from reservoir water to bar ditch water) and never found a sample that didn't contain some amount of both aerobic and anaerobic bacteria. Most of the water in gathering systems is condensation, but just a few drops of produced water can start a colony who's growth is subject to an exponential growth curve. Whoever is saying that the occurrence of MIC represents a "mess up" doesn't know what they are talking about. I've investigated dozens of pipeline failures and all of them have been MIC and most have been symbiotic co-colonies of APB and SRB (straight wall pit for a couple of mm followed by the SRB "ice cream scoop" signature). Every sample of pipeline accumulated water I've ever sampled (and I take a sample every time we cut a pipe on one of my jobs to test for pH) has had a basic pH, but that does not include failure points since the water and the colonies are long gone when someone finds the leak. We worry about CO2 corrosion in gas gathering, but I've never seen it. Not once.

David Simpson, PE
MuleShoe Engineering

"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.

 

[SJones]

Good that the Ol' Boys didn't try to mitre the GRP. Indeed, methanol is not good for the health or the pipeline as a great source of oxygen. Did you ever pinpoint where the bugs came from in your failure investigations? The first source is usually the drillers and the next is the hydrotest water.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[BigInch]

Never used a pig in a gathering system. It now occurs to me that a possibility might be to build in some temporary "end-of-line" connections on trunklines to new well clusters.

It can be a good idea to build in taps for future connections every mile or two in areas "of great expectation", those areas that haven't been drilled yet, or for looping what might become a trunkline later on, should a certain area's production increase more than expected. Trying to figure out where a field compressor might want a home some day, I'd put in a double tap every 10 miles, with a block valve inbetween. One tap for future suction and one for discharge of a new field compressor site. Try to keep your options to make changes as open as you can.

David, thanks for the cost info on the RTP.

BTW that's what made that paper interesting. Another indication that you can find any and all things in just about any given typical gathering system... as you well know.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[zdas04]

Like I said, every single sample I've ever sent for an analysis of microbes has been positive. Drillers are often responsible for a reservoir going sour, and could be the source. Most failures have been years after hydro (and many of the lines were never hydro tested, either just not tested or tested with air/nitrogen). I always felt that it was more important to find ways to prevent future failures than try to find the bugs since there really isn't anyway to kill a colony 100%.

The way I found was pigging. Every single line I design has pigging facilities. For single well lines I use pigging valves. For bigger lines I build launchers/receivers. For networks I use piggable drips to bring lines together. Nothing else works.

David Simpson, PE
MuleShoe Engineering

"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.

 

[BigInch]

You're right. All the newer gathering systems are adding at least some pigging capability.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[ChEMatt]

David,

Can you elaborate on "piggable drips", please?

Can any of you elaborate on "looping". What is it used for?

One more question for all, what are your thoughts on automatic pig launchers and receivers? How often are they used? Pros and cons? Design considerations?

Onwards,

Matt

 

[zdas04]

Last one first. Automated pig launchers are a truly bad idea in gas gathering. They only work with spheres, and spheres are a terrible compromise that are only useful for separating products in a batch liquid line (where the trailing liquid tends to compress the sphere so it slides more than it rolls). In gas gathering the just roll over the stuff you are trying to remove.

Piggable drips are an innovation that I invented 15 years ago (while I worked for a major company that would have owned the patent so I didn't patent it and have published details a dozen times, they are in the public domain) to solve the problem of bringing two piggable lines together in a remote location that was not accessible 10 months out of the year. The first version (there is a picture at page 140 in the document I referenced in the first post in this thread) has a lateral fitting inside of a larger pipe. The interaction between the two streams tends to start a swirl and sling any water into the slots cut in the main line. I've put 20 of these in systems around the world and they really work great, wish I could have patented it for my own account. I built a couple with the branch smaller than the run. These are a little tricky to operate. You run the small pig and let is stop in the big line. Then you run the big pig to push the little one into the receiver (the little ones always come in pretty chewed up). The most radical network I've built uses one pig receiver for 6 pig launchers. It works really well.

No one ever designed a gas gathering system of any size that had the right size pipe going to every well and within every trunk. No well is ever "average". This means that within the system you do your best while knowing that some of the lines will be way too big and others will be way too small. For the lines that are too small, you can reduce the pressure drop by "looping" the line which means to run a second line for the same service. A simple loop follows the original route. These are occasionally the best answer, but I rarely end up with a simple loop. It is common to run the new line in a new direction to solve several problems at the same time, it is also common for this activity to reverse the flow the first line. If that happens then you need to think about how pigs will run in the original line (usually you just turn off the loop long enough to run a pig, but sometimes you turn the original launcher into a receiver and vice versa).



David Simpson, PE
MuleShoe Engineering

"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.

 

[ChEMatt]

Ahh, looping = sistering. Right after I posted that I remembered hearing that term in my previous life.

I'm sure I'll come up with some more questions. I do appreciate you guys' willingness to explain/help. Thank you!

Onwards,

Matt

 

[BigInch]

Sistering??? My imagination is running wild. Is that anything like dating twins?
Looping is just laying a new line parallel to an existing line. Northern Natural Gas, for example, has 3 and sometimes 5 mainlines, 30 to 36" diameter, all running parallel for hundreds of miles.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek