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]

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.

 

[BigInch]

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

 

[zdas04]

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.

 

[BigInch]

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

 

[ChEMatt]

"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

 

[zdas04]

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.

 

[ChEMatt]

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

 

[zdas04]

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.

 

[BigInch]

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

 

[ChEMatt]

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

 

[zdas04]

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.

 

[SJones]

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.

 

[zdas04]

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.

 

[ChEMatt]

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

[ul]
[li]Consider wellhead compression, but the client might not want it[/li]
[li]Low velocities may lead to corrosion.[/li]
[li]Take the shortest route from point A to point B, unless there's a really good reason to make a turn.[/li]
[li]Always keep pigging in mind when making bends, loops, and anything that isn't a straight run.[/li]
[li]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.)[/li]
[li]A class may not be beneficial/necessary given my experience.[/li]
[li]Typical gathering lines (non-DOT) are not inspected for corrosion.[/li]
[li]A large portion of corrosion is MIC[/li]
[/ul]

Another question. Are there periodic inspection ports or above-ground stubs to allow inspection, future connections, chemical injection, etc.?


Onwards,

Matt

 

[ChEMatt]

BigInch, can you elaborate on RTP?

Onwards,

Matt

 

[zdas04]

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.

 

[BigInch]

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

 

[EmmanuelTop]

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

 

[BigInch]

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