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Design of Gas Gathering Systems
4

Design of Gas Gathering Systems

Design of Gas Gathering Systems

(OP)
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

RE: Design of Gas Gathering Systems

You might have gotten better traction in Pipelines, Piping, and Fluid Mechanics Engineering, but most everyone who goes there comes here too, so you haven't messed up much.

Available classes (including PetroSkills) are very much children of the cross-country pipeline family. An awful lot of what they cover is from that perspective (e.g., rather than teaching you what is important in ROW acquisition they point you to your land/permitting department, gas is assumed to have been dehydrated, gas is assumed to be at pretty high pressure, compressors deal with pretty clean gas). Much of what is covered is not applicable/misleading for a blood-guts-and-feathers gathering system.

I teach a class more focused on gathering, but right now it is not scheduled anywhere (and it is kind of expensive). JM Campbell has a version of my 5-day class (at one point they asked me to teach it but we couldn't come to terms on content) that is put on a couple of times a year (it is 30% more expensive than my class), but the focus is pretty strongly from a plant perspective (JM Campbell has that heritage) and I thought the gathering and compression sections were a touch weak. Stuff from ASME or the Pipeline Industry would be a waste of time (I cover B31.8 in 2 slides and some scattered references, ASME has a week long course on it).

The predecessor to my 5-day class was a 2-day class that had quite a few beginning field-facilities engineers attend, and they tended to give it good marks. You can find the handouts from that class at MuleShoe Engineering Samples The stuff I think is important for gathering starts at page 115 and goes to page 225. That document was a classroom handout and was intended as a place for students to write down what I said in class so there is a bunch missing (you'll have to fill in the blanks), but it should give you a flavor for the topic.

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.

RE: Design of Gas Gathering Systems

Don't pay for anything. You've got enough experience to jump into it. Besides, gathering systems are not regulated, therefore, you can't hardly mess up, even if you wanted to. I did the same thing in the 80's. After several years in engineering companies designing national pipeline transmission systems, I found myself out in the gathering system nether lands. Muster up some confidence and just follow your instinct. You'll get some good experience putting together stuff with second hand equipment, company stock, modified and jury-rigged patches... and other stolen goods.

When they ask you what you're doing with all the glycol you're stealing, tell them if they upgraded the dehy they wouldn't be losing it all by blowing it into the downstream pipelines.

Have fun. Don't speed on the lease roads.

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

RE: Design of Gas Gathering Systems

I just followed the link to the PetroSkills class and it is the JM Campbell course I was talking about. The three named instructors are VERY qualified plant guys (I don't know the two new guys that are teaching it). This is a class where the instructor has to really believe that chemical corrosion inhibition works in low pressure gas gathering lines (I have data that shows it doesn't work even though everyone is pumping the hell out of it).

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.

RE: Design of Gas Gathering Systems

small diameters and high velocities helps keep them clean, but will increase the required pressures. I only had those problems in gas wells that were depleating and left slow velocities in the branch to the well. Fortunately we would shut in the well and close off the branch before the corrosion rate caught up with it. I've heard of a lot of gathering systems trying to go with RTP now. I guess they're planning on longer well life.

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

RE: Design of Gas Gathering Systems

(OP)
"Don't speed on the lease roads."

NOW you tell me... Ask me how many flat tires I've gotten because I don't like inching along gravel roads in WY... Need 10-ply.

Thank you both for the kind replies, and especially thank you David for the link to the presentation. I'll be going through that tonight.

I had one follow-up question. BigInch says that gathering systems are not regulated. How does a DOT pipeline figure into a gathering system? One of the compressor stations I built was on the receiving end of a DOT pipeline, thus my familiarity with the CFR. What would cause a pipeline to be "DOT" versus not?

The big problem is during an interview when asked about gathering systems I'm going to be at a loss. But if given an opportunity I figured I'd just review someone's project files and see what they did, head out to the field if I can find a pipeline project somewhere, and look at existing simulations of gathering systems. ROW would be something new for me, but wouldn't we have a landman or someone to work that out? Using simulation software is second nature so I think the sizing of the lines would be straightforward. Routing them, however, is something about which I'd have questions. Looking at contour lines/maps and deciding costs for routing around mountains vs. elevation changes, etc. In my mind it would become more complex, but perhaps I'm too worried about that?

Onwards,

Matt

RE: Design of Gas Gathering Systems

That is kind of the common wisdom, then you add in that they want sub-30 psig wellhead pressures and all of those high-velocity dreams go out the window. Most of the stuff I'm looking at right now (mostly Shale Gas and CBM) is expecting 50-100 year well life. Most of that time at pretty low pressures and no one wants wellhead compressors. Pipe gets big and people don't want to pig lines. It is amazing how often I see "designs" that are 30% [mostly inappropriate] Engineering and 70% wishful thinking. Makes for a good living fixing that stuff.

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.

RE: Design of Gas Gathering Systems

(OP)
So it sounds like there's a balancing act between corrosion and velocity? Is it caused by stagnant liquid not swept away by the gas? Why would people not want to pig lines? Because it requires the wellhead compressors?

Onwards,

Matt

RE: Design of Gas Gathering Systems

Mostly people don't want to pig because the see it as eating staff time. Mostly producers are not terribly comfortable with the stuff you need to do to gather gas. Many of the lines I see are just REALLY long separators (it is not uncommon to see bulk velocity in a gathering trunk under 0.1 ft/sec) and water stands at every sag. Most of the water is condensation which is pretty benign, but a bit of it is produced water with some amount of bacteria in it. Virtually every corrosion failure I've ever investigated in gas gathering has been MIC (I did have on failure from failed coating in a line with no cathodic, but all the internal failures I've seen have been MIC).

Low pressure gas gathering is really a different breed of fish from mid-stream. Very few of the people who can accept that concept started out in mid-stream or cross-country pipelines. Those guys seem to come in with an attitude that prevents accepting the facts in front of their eyes (when I started in field facilities, the gathering system I had responsibility for was spending $10k/month on corrosion chemicals, I stopped all chemical injection on day one, when I retired 10 years later my replacement reinstalled all of it and cranked it up to $25k/month and of course she blames me for the corrosion failures that started happening when she replaced pigging with chemicals).

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.

RE: Design of Gas Gathering Systems

With wells coming on and going offstream, or with depleting flow rates, gathering systems are a constant battle and it was frustrating in the hydrdaulic planning sense. Geologists are the most optomistic people on earth!

Just draw a straight line and have a really good reason for getting off of it.

DOT lines usualy start downstream of the first separation plant, although (I think) there are a few new exceptions based on population, or crossing public highways, or something. I haven't worked in the US for 22 years, so I am not up on the latest interpretations of those finer points. There's a diagram in the B31.8 code appendix that shows more or less where the demarcation lines are... more or less.

Out at Painter Reservoir, it was all BLM land, so the only landowner was the US Gov. Hope you like the color "BLM green". Stock up on it.

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

RE: Design of Gas Gathering Systems

(OP)
zdas04, BigInch, unfortunately eng-tips prevents me from thanking you multiple times on the same thread. They used to not do that. Just wanted to say thanks again for your help.

The units I worked on were "BLM Tan". I kinda like it. Like khakis for compressors. "MIC" - Microbiologically influenced corrosion. (What did we do before Google???)

Are pipelines not periodically inspected for corrosion? Do folks not use "smart pigs" often, or ever? Can those units not detect pipe wall thickness and/or corrosion?

What's the lowest pressure in which you can use a pig?

Onwards,

Matt

RE: Design of Gas Gathering Systems

Non-jurisdictional (not DOT) gathering systems are basically never inspected below ground for corrosion, and most lines are not piggable (in spite of several people like me screaming about it for a couple of decades) let alone able to run a smart pig. Smart pigs can do wondrous things (better every year), but mostly their use is limited to mid-stream and cross country lines (and not nearly all of those).

Pig runs rely on dP not absolute pressure. If I apply 2 psid to a 10-inch (which has a contact area of 79 square inches) then I am applying a force of 158 lbf. A 10-inch turbo pig weighs about 25 lbm so 2 psid is adequate to overcome something over 125 lbf of friction resistance. I've run pigs in lines with a vacuum at the foot.

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.

RE: Design of Gas Gathering Systems

Provided that there is access, there are tethered and crawler ILI tools, but I guess that the loss of production versus the risk of failure equation doesn't really get tested in the situations under discussion.

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.

RE: Design of Gas Gathering Systems

I never much saw the point of a tethered tool. The tether length is long in terms of carrying the damn cable around, but pretty short relative to gathering pipe. I've run tethered cameras a few times and found that they generally ran out of rope just before the feature I was interested in. I'm most impressed by the internal bypass in-line inspection tools that can maintain an approximately constant velocity and not slow down when they hit a sag full of liquid (which tends to confuse most pigs, they don't have a very big brain).

The problem with most gathering systems is that not only did the "designer" not consider pigging, he made choices that preclude pigging. I worked on a line last year that for some reason lost in the mists time had a pipe mitered at around 60° followed by about 3 ft of pipe another miter around 50° the other way followed by 6 ft of pipe followed by a pipe mitered to 115°, etc. At the end of this sculpture (not a single fitting or square weld) the pipe was pointed about 40° away from the original path. I would be scared to death to put a ball pig in this line and we were trying to pull a liner through it. Don't think smart pig would have been an option. This was an especially bad example, but most every line I find has garbage like this (one guy thought the right way to start a loop was to bring the line into the branch of a barred tee and the two loops out of the run on the tee, not terribly piggable).

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.

RE: Design of Gas Gathering Systems

(OP)
So what I've gathered so far from the responses for design of gas gathering systems is:

  • Consider wellhead compression, but the client might not want it
  • Low velocities may lead to corrosion.
  • Take the shortest route from point A to point B, unless there's a really good reason to make a turn.
  • Always keep pigging in mind when making bends, loops, and anything that isn't a straight run.
  • There is continued discussion on corrosion inhibition and whether or not treatment chemicals are truly necessary or even effective. (I found a paper on the subject but I haven't forked out the $10 for it. Might be interesting reading.)
  • A class may not be beneficial/necessary given my experience.
  • Typical gathering lines (non-DOT) are not inspected for corrosion.
  • A large portion of corrosion is MIC
Another question. Are there periodic inspection ports or above-ground stubs to allow inspection, future connections, chemical injection, etc.?

Onwards,

Matt

RE: Design of Gas Gathering Systems

(OP)
BigInch, can you elaborate on RTP?

Onwards,

Matt

RE: Design of Gas Gathering Systems

Corrosion inspection ports (coupons) are a horrible indicator of risk. They are never in the place where the corrosion happens (water collects in every sag and most lines average an overbend that creates a sag every 3-5 joints. There is no way to predict which ad hoc pool of liquid will become home to colonies of APB (acid producing bacteria) or SRB (sulfur reducing bacteria), in my experience it is never the place where the coupon sits.

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.

RE: Design of Gas Gathering Systems

Reinforced Thermo Plastic Pipe. I don't have any personal experience with it, but it looks very interesting. I've only read up on it recently. It's been around for 7-10 years or so. It's a thermo plastic HDPE type and then it's wound with two layers of strongly reinforced plastic covers, one in each direction, then an overcovering on top of that. It has been used with apparent great success in the desert gathering systems in these parts and is finding it's way into some gathering systems in Canada and I think North Dakota, Montana. I saw that there was an application asking for a permit to use it in downtown Los Angeles (Class 4 area I think) of all places, that was supposed to be ruled on a couple of months ago. I haven't had time to check up on it to see if it was allowed or not. First use in a class 4 area. I will see if I can find the name of the company that made the stuff. It comes in 700-800 foot spools. The difficulty is that it requires some skill to connect spools together. It seems to be competitive with steel, and maybe more so when considering it's use in a corrosive environment.

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

RE: Design of Gas Gathering Systems

Sorry for jumping into this thread but it is rather interesting and it tackles a lot of issues raised during the project I have been working on.

I see that low velocities are quoted as a promoter of corrosion. On the other hand, in a similar thread I raised a few weeks ago, low velocities were recommended due to the fact that significant quantities of sand are present in the production stream (Methane + produced water). The gathering system in question was also a low-pressure network (3 barg central manifold pressure).

Being in such position, it seems like there is no way out: I need to maintain low velocities in order to avoid erosion, but at the same time it looks like we'll suffer from corrosion because we have sized the flowlines very generously to mitigate the erosion effect.

Is there any way around this problem?

http://antwrp.gsfc.nasa.gov/apod/astropix.html

RE: Design of Gas Gathering Systems

Yes. The way out is to optimize the design. That puts you in the best position between the rock and the hard spot. Not a great place to be, only the best.

If that is enough to sweep the line of accumulated liquids and sand you're at least not going to suffer lost production due to plugging and slugging, so you must at least keep that.

You might also estimate the loss of wall due to corrosion as a function of velocity (maximum at zero and minimum at sweep velocity), then estimate the loss of wall due to erosion as a function of velocity, (minimum at zero and maximum at your maximum velocity you now calculate as your design velocity). Plot each function separately and where they intersect, that should be the optimum velocity. It will tell you what to allow for erosion-corrosion loss, then design your pipe wall to last for whatever period of time you figure your well will produce economically (design life of the branch).

Now some questions.

What velocity did you settle on? Is it single phase, or two phase flow? What flow regime do you have, mist, annular, wave, slugs, bubble, foam on liquid, etc.?

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

RE: Design of Gas Gathering Systems

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.
  • 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
  • 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.
  • 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).
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.

RE: Design of Gas Gathering Systems

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

RE: Design of Gas Gathering Systems

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/industryOp...

http://www.capp.ca/library/publications/industryOp...

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.

RE: Design of Gas Gathering Systems

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.

RE: Design of Gas Gathering Systems

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.

RE: Design of Gas Gathering Systems

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

RE: Design of Gas Gathering Systems

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.

RE: Design of Gas Gathering Systems

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

RE: Design of Gas Gathering Systems

(OP)
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

RE: Design of Gas Gathering Systems

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.

RE: Design of Gas Gathering Systems

(OP)
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

RE: Design of Gas Gathering Systems

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

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