The Denver gas situation

There was a short period of time last Saturday when Denver was subjected to a rolling blackout as demand met up with a limit on natural gas supply.  The company has now explained the problem (under the fold).
Frigid weather -- including a record low of minus-13 degrees Fahrenheit in Denver -- was at the heart of the problem, sending power demand soaring as homes and businesses turned up their heaters.
When the weather gets that cold, it can freeze wellheads -- the equipment that controls the flow of gas from the Colorado and Wyoming fields that Xcel power plants rely on to generate about half of the company's electricity. That's what happened Saturday. Heneley said he believed it was the first time the company resorted to power cuts in the winter to avoid collapsing the grid.
The outages affected about 300,000 Xcel customers in the Denver area, with customers in Eagle, Grand Junction, Vail and Aspen also briefly losing service.
Heneley said that demand on Excel's portion of the Colorado power grid peaked Saturday somewhere between 4,100 megawatts and 4,400 megawatts, which is far off the summertime peak of 6,500 megawatts.
 Similar low temperature problems were raising concerns in Russia last month, and in some parts of Eastern Siberia, such as Sakhalin Island, they either close a lot of the field down, or reduce production, until the warmer weather comes in the Spring.
Yeah, I lost my power Saturday morning. I live in Boulder. One question I have is that while the summertime peak may be 6,500 for electric generation, but what about home heating? A lot of houses around here have natural gas furnaces, and if I'm reading that correctly, THEIR methane use isn't included in the 4,400 number.
I wondered about that too - they quote the peak electric generation number to show that their grid still had capacity, but I was more concerned that they had run short of NG.  And the max elecetric generation number doesn't say anything about the max N useage.
Now I know why my power went down.
And yet, people in the business are claiming that natural gas wellheads should never freeze.  "Aflatoxin" at said:

Natural gas wells are probably not going to freeze.

They use Dehydrators at the well heads or CDP, and just in case, there is plenty of Methyl alcohol. Once the gas makes it into the interstate pipeline system, it is bone dry, about 95% methane, 2% N2, 1.5% CO2 and a little ethane and heavies.

Water is a big problem in pipelines, the gas people worked out ways to remove all of it 50 years ago.

so your saying the freezing story was a cover story rather then admiting a sudden production shortfall?
I honestly don't know.  The Denver Post paints a much more complex picture:

Mechanical malfunctions, inaccurate weather forecasts and inadequate natural-gas supplies caused the rolling power outages that afflicted 325,000 customers of Xcel Energy on Saturday.

It marked the first time in Xcel's institutional memory that controlled electrical outages occurred in the winter.

Such disruptions typically happen on the hottest summer days when demand for power peaks.

Three outages of 30 minutes each hit customers in portions of metro Denver, Grand Junction and the central mountains. The outages lasted longer than 30 minutes for about 25,000 customers.

"The phrase 'perfect storm' is overworked, but we've never seen events like this," said Xcel spokesman Mark Stutz.

Portions of three coal-fired power plants in Colorado were out of commission Saturday morning, either for scheduled maintenance or because of mechanical breakdowns.

In addition, Xcel had inadequate supplies of natural gas on hand because initial weather forecasts had not suggested the record-breaking low of minus 13 on Saturday.

The utility had enough natural gas for all of its customers' heating needs, but it ran short of the fuel to supply gas-fired power generators that supplement the electricity produced by coal-fired power plants.

The gas shortage was exacerbated by an undetermined number of Rocky Mountain natural-gas wells whose pumping equipment froze, preventing additional deliveries.

The idea that one natural gas production equipment failure could cause Xcel to need to take down the grid would make sense ONLY if there were very little spare supply.

Also, this stuff about 30 minute blackouts isn't terribly accurate. It was more like 45 minutes to an hour. And it wasn't until later in the day that the cause, a natural gas shortage, made it into the media.

It is not gas that may have froze, but water condensation that slowly built up.  Eventually the passage for the gas narrowed.  Until that passage was cleared, getting gas to the customer became more difficult. (That is how I understood the "freezing.")

However, the story did mention a shortfall, as well as the freezing.

Someone from Denver should address this issue.

As I understand it, there should be no water in the natural gas at that point.  They have hundreds of dehydrators at each wellhead, as well as other ways to remove water and anything else that might freeze.
There usually is only 1 to 3 dehydrators to a field, which could have many wells, often up to 50 miles away from the last well in the gathering network. I worked a gathering system in south Texas for a field of 860 wells. We had 3 dehydrators at the 3 outlets from the gathering system network all about 50-60 miles distant from eachother. The wells had enough pressure to flow to those outlet points by themselves, but required a number of 1500 HP compressors to kick up the pressure enough to get into the intrastate gas transmission company's lateral lines. That's where we put the compressors. Compressors and flow meters can't take liquid slugs, so all liquids had to be knocked out beforehand. After the liquids are out, you can run the gas through a scrubber to eliminate the H2S (if you have any of that nasty stuff), then dehydrate the rest of the gas stream, compress it and lastly, meter the flow to the transmission company, so it was much more convenient to minimize the installation all of that equipment to the fewest number of places as possible.
The gathering field lines freeze between the wellheads and the first glycol dehydrator, which in many cases can be up to 50 miles away from a well.  In the gathering lines there can be a mixture of oil, water, salts, condensates, paraffins, waxes, NG, CO2, N2 maybe H2S.  Hydrates are crystals where water is embedded in gas molecules.  Any significant quantity of hydrates can plug the gathering lines.  Hydrates can form at temperatures above 32ºF.  If temperatures drop below 32ºF, then ice plugs can also form.  A lot of wellhead treater installations have heaters to keep the flow into the gathering lines above the temperatures where hydrates form.  Normally the well heaters are off unless hydrate formation temperatures are expected, in which case an operator will go out to the field and light up the heaters.  Even if the heaters are lit, they can still go off if hydrates form upstream, as this can shut down their fuel supply which also comes from the well.  In my experience it sometimes not possible to reach the wellheads in time to light the heaters and keep them from freezing, because of downed trees, and snow/ice on the roads and access trails.  It is also not uncommon for somebody to  get sick on those cold nights either.  Of course extremely cold weather usually happens on the weekends when there is only one person on call.
Someone who claims to have worked directly for this particular company says they have hundreds of dehydrators per wellhead.  He didn't think it was likely that anything would freeze, even with equipment failure.
If he worked for the local distribution company, or the intrastate or interstate company, he is probably correct. In those systems the gas would not be subject to freezing. If he/she says they h/s worked at the company operating the gas fields, do a detailed check his/her credentials. The company I worked for was one of the largest independent drilling and gathering operators in the US at that time (we had more gas wells and gas flow volumes than Exxon produced by themselves) at the time. The only other thing that could possibly have happened (within my reasoning) is that the Denver local distribution company (LDC) had thier peak gas diverted by their intra/interstate supplier to other customers that were experiencing greater hardships or had contracted for more firm transport capacity than Denver. Normally, as was suggested by other posts, various customers will request a firm volume that the intra/interstate transmission company must guarantee to transport and another peak volume that the intra/interstate transmission company will transport only if he can reasonably do so. They will follow that SOP unless an emergency is declared, in which case they will revert to making special volume assignments according to priority level of the services that are affected. Could have been one of those things. I've said all about I can say without having been sitting in the control room myself, so ... I'll definitely leave any further details for the LDC to explain away.
He says he worked for CIG, before it was acquired by  El Paso.

He also said all of CIG's wells are in steep decline, except the Jonah field in Wyoming.  And their plants are not in great shape, either.  

He's right then.  I never heard of Xcel. I left the USA in 1990 and there's been a lot of takeovers since then, but I do remember Colorado Interstate Gas and most of their immediate supply wells were in the Tx-Ok panhandles and SW Kansas.  Those were the old gathering systems in which I was trying to turn one around to supply a proposed peak generator in Larime Co.  They were some producing wells still left around that particular area, but they were on their last breath 16 years ago and were running at about 30-40% N2, so even then they wern't what you would call star performers.
But he's still wrong about having hundreds of glycol treaters.  There's only a couple of those per field.
Xcel used to be called Public Service Company.
The only XL that I heard about before was Microsoft's.  I'm surprized they don't sue Excel for some name infrigement violations.-)
There's still one aspect of this situation that I find confusing.

People in Denver are heating their homes primarily in one of two ways. Either they are using natural gas, or electricity. At the same time, the electricity is largely generated by natural gas.

Now, these rolling blackouts were of electricity. AFAIK no natural gas supplies were interrupted to anyone's houses.

The main question is, did demand increase for natural gas for heating purposes, leaving less available for electrical generation, hence the blackouts? Or is natural gas for home heating somehow handled separately and independently from the supply available for electricity?

We see all these figures about electrical supply and demand in terms of so many megawatts, but never any figures for how much natural gas is being supplied or consumed. In theory, it should be just as possible to have natural gas shortages to end users, as electricity shortages; and then we could have natural gas "brownouts", reducing gas pressure in the system. But you never hear about this kind of thing.

The whole issue of how gas and electricity supplies are interrelated has been brought into perspective by this situation, but nobody seems to be explaining it clearly.

My understanding is that industrial users (including electricity generation) have contracts that are lower priority than individual househould users.  This priority setting might even be the law, since gas brownouts for houses with old pilot lights could be a big problem (once the gas pressure returns, that is).

In any case I think the industrial users get a discount to make up for their lower priority.  And presumably when there is a danger of low pressure somewhere, someone in the gas flow chain decides which valves to close down when.  Actually, I'd be interested to know who makes that decision, and where.

You are correct, that there are various levels of firm and interruptable service contracts that exist amongst the different types of users.

Electricity supply can be affected, because gas supplies a lot of the fuel for base electrical load generators and much higher percentage of the peak electrical demand generator capacity.  When the gas supply is not available, the peak generation capacity is usually lost exactly at a time when it is needed the most.

The gas distribution companies these days are usually not the same companies that operate the gas wells in the gathering fields and have little control over what goes on out there.  That is left up to the field operating companies.

The field operators supply their gas to intrastate transmission companies and they in turn might supply gas to local distribution companies and also to interstate gas transmission companies to move to farther out marketing areas.

Normally all gas quantities are set up about 30 days in advance, based on last months demand, traditional use patterns, long term weather forecasts and excess capacity transportation requests that some customers make from time to time.  This information is continuously updated, but unexpected weather and unusually high demands sometimes screws things up.  This is especially when the weather is so bad as to affect the well supplies in the field (see other posts above).  

When field supplies are affected, the gas transmission companies sometimes can make up the difference in any stored supplies they may have.  Unfortunately, there are not too many storage locations in the whole of the US.  If the gas transmission companies do not have their own (or contracted) storage volumes to draw upon, they can survive for a limited amount of time on the pressurized gas they had in the pipeline when the supply shut off.  The time they can survive depends on the number of pipelines they have going to the affected area, the length, diameter and the pressure the pipelines had when the supplies were shut off.  For a large capacity pipeline system, this can be days.  For a small distribution company located rather close to the supplying gas field, it may only be a matter of hours.

The coordination of all of this process is handled by the gas transmission company's marketing division that makes the demand projections, the maintenaince division which keeps everyone updated with the latest capacity statistics and the operation departments, which monitor realtime flows into and out of the system and all along the pipelines, usually from a centrally located gas control station in the basement of their headquarters (in some cases 1500 miles away from their primary source wells).  From there a 1 or a few gas control operators watch the remaining flows and pressures and bring on supplies from storage or other areas if they can.  Automatic controls can open/close valves, start compressors and flow paths between subsystems to try to solve the problem.  If everything fails, the gas controllers will start issuing warnings to emergency authorities and hospitals and other critical customers on when they will be out of business, so emergency generators at those locations can be warmed up and running in time to deal with total loss of supply.  

Its quite a complicated process to coordinate all of those continuously changing variables and really it is amazing that it only fails the few number of times it actually does.  The gas controllers today have advanced realtime SCADA systems, realtime pipeline hydraulic simulators they can run what-if scenarios and genetic and neural network algorithms figuring up to the minute supply and demand patterns and corresponding optimum flow path and compressor settings to maximize flows while minimizing power consumption.  Usually all of this goes on without anyone taking notice (or handing out any attaboys either).  To design a 100% failsafe system would require an investment of about 10 times that of the 98.5% reliability figure that they usually try to maintain.  

Thanks Gets IT; I love learning this stuff!
Surely you jest, but it is nice for me to at least feel that I'm appreciated from time to time. Thx.
I second the encouragement. It is allways intresting to read about system thinking and real world trade offs.  Manny people here have too magical views on how things work and how they are robust or fragile.
Seconded ... that was a very informative post.  I have a bad feeling that in the future we'll all need to know more about how the gas infrastructure deals with shortages.
Halfin's question is the best of the day. dp1's answer is the best and basically correct. It has to do with industrial vs. residential contracts.
It is not uncommon for a large or medium electric generator to have a special lateral going directly from the mainlines supplying a city right to their generating stations.

"Town Gas" may be delivered through several pressure reduction, metering and mercaptan additive stations scattered at various locations throughout the city.

I have taken a look to see what I can find out about Xcel Gas while I sit here in Spain.  The website has some interesting stuff that you can kinda' get an idea of what's going on.
They appear to be mostly interested in generating and transmission of electricity.  I can only find one obscure reference to gas transmission,,3080,1-1-1_16699-14983-2_171_256-0,00.html
click over to the right on,
Natural Gas Transportation information
where you get connected to Public Service Co of Colorado
In the menus there,

<restriction history> shows common winter flow order days
The flow order policy is explained in the <new> OFO Gas Days just above.

<gas transport supplier list>  Interesting!
shows that they can (maybe) get gas from a lot of sources from many different companies.

<load forecasting tip>  Very interesting! they explain to their customers to review their load requests for various low temperature forecasts.  Not uncommon for customers to ignore these and just stay with their usual nomination.


<Nomination Procedure Review>  Here's how large consumers schedule their deliveries.  Note:  they don't work weekends.

A lot of utilities have this kind of stuff on their website and its surprizing how much you can find out if you want to.  Another place to try is at the website of the State Administrative Office that regulates utilities in your state, ie. Texas Railroad Commission, etc.  Sometimes they even have detailed maps for all electrical lines and pipelines in each county available online.

What I find most troubling is the fact I have not heard a word of this on the MSM.  Granted, I do not watch much TV, etc. so I may have missed a small blurb.  However, 300,000 Americans dealt with rolling blackouts in sub-zero weather this weekend.  Why the hell did this not make the front page???  

Of course, kudos to TOD for bringing us the info.

Hundreds of thousands of people in upstate New York were also without power last weekend.  Some still are.

Kunstler's power was off until midday Monday, making his blog update late.  He was surprisingly unprepared.  

Wow, unprepared is right.  You'd think that a guy who spouts as much "wisdom" as he does would have his ship in a little better shape.  His only phones rely on the grid?  Sitting close to the gas stove for heat?  Hmm.
And despite all his talk about the virtues of community, he doesn't seem to know his neighbors.  
Nope, not a peep on Network TV. Heck coverage of Nigerian situation and even W's "energy breakthru's" was absent as well. Are the news people that oblivious?
Okay I have a question for the knowledgeable posters here.

I live in the midwest and rely solely on NG for heat, hot water, and cooking.  The whole grid for heating is based on NG, no oil burners at all.  Obviously secondary heat and cooking is based on electricity.

How do I build a redundant system if both my primary and secondary heat is based on NG?  Yes I have a wood burning stove already but it is only for heating some of my livable space and I can't cook with it.  

Clearly there is coal fired electric generation but it sounds like all peak capacity is based on NG which will be the first to get shut down.  If we get in a really short supply situation is it the consensus here that residential NG supply will be the last to go down?

Thoughts on possible scenarios and options?

Try checking out the local bottled LPG supply situation.  You might be able to get a couple of bottles and a room heater or two.  They also sell small portable camper's stoves you could use to cook simple things in emergencies.  A long time ago you could buy refrigerators and other appliances that ran on LPG too.  My grandfather had a frige like that out at his lake house up in the middle of Lake Superior.  
Domestic gas should be the last supply to be interrupted, but if it is would probably take the longest to get back due to possible explosion risks. There is likely to be a phased conversion to 'town gas' based on coal should NG supply become insufficient and infrastructure remains intact.

You could get an additional or replacement wood burning stove that enables some cooking. You could build a wood fire for cooking and a wood fired oven, if adequate wood supplies are likely. A solar cooker is surprisingly effective for long, slow cooking. Bottled gas cookers are good but bottled gas is expensive, might be worth having for a medium term stopgap. I have begun to look into generating biogas for cooking, probably only worthwhile if you keep animals (pigs, cows in particular). A small multifuel camping type stove could be useful in emergencies.

For cooking and heating I have about five backup systems. My advice is to keep it simple. An old-style potbelly cast-iron stove can burn coal, wood, wood pellets, and probably corn cobs (though I've never tried that fuel). An alcohol stove (as found on some large sailboats) is safe and simple. Kerosene is a marvelous versatile fuel for heat, light, and cooking. Personally, I dislike gasoline and propane because of the explosion hazard with those fuels.
If you have a huge bank of storage batteries charged with wind turbines or photo-voltaic solar chargers, then 12 volt technology is both robust relatively simple. And, of course, with an inverter you can run any 110 volt A.C. appliance on 12 volts.

For a thorough understanding of survival technologies, I suggest a close study of Native American cultures from the northern United States and Canada. Also, if you study how farmers got by a couple of hundred years ago, you will learn useful things.

Thanks to all for posts.

I have read widely on and can do the survival skills and am comfortable going that route if TSHTF.  I really am interested in maintaining current living space for my family and above suggestions are great and an addition to what I currently have.  I have multiple camping stoves and fuel, barbecue grill, and fireplaces and will be adding rain barrels soon.  I am already in a small but old and rock solid house space.

What I am digesting is if/when the grid supplied energy is going to become unreliable.  I have researched wind and solar as options for electric supply, along with storage.  I am optomistic that biodigesters and methane sources may augment the existing NG supply in my region.  I just wanted some comments on how that supply was liable to get distributed.  I have a better feel now and can set timelines for getting off the grid.

You are  probably already well ahead of 99% of the US population, and certainly ahead of me. Would be good if you could report back on the relative merits of your methods sometime in the future, there would be many here who'd appreciate it, I'd guess.
If anyone really wants to know detailed information about how gas gets from 20,000 ft down under through dehy, storage, LNG tanker, whatever... to your 2nd home in Italy, you can see a pretty good website by the Italian Gas supplier ENI (in English)

Too bad Excel's website isn't this good.

Picture of a Gas Control Center.  Notice the cool Italian sweeping design look!

the red lights in clusters are compressors turned on or off.  The lights by themselves are valves between transmission lines, laterals and local distribution divisions within the system.

Its getting cool.  Time to turn that electric heater on.  No local gas pipeline distribution sys in my area and the bottled gas is a hassle.  
click on the control panel and you get directed to a page where you can,

  get some daily flow figures, and trends.

down in storage menu, there are some nice diagrams and pics
with links to,
Treatment shows the dehy columns
Compression from 1125 to 2700 psi for storage injection

<Gas storage in Italy> shows all storage locations and links to technical details of each site.

<LNG Dossier> shows just about everything you ever wanted to know about LNG and how its tanked around my front yard in the Mediterranean Sea.  On a clear day I can see 'um out there.

<Gas Pipelines Dossier> Everything you wanted to know about how gas gets to Italy and how its transported and used.

links to gas to the home and the industrial infrastructure are good.  hack away there.

<National Grid Pipeline Network> gets you to a nicely detailed map of Italian pipelines downloadable in pdf.

Over to the right <Information to shippers> you can get  highly detailed maps of the entire distribution system in Italy. Just keep drilling down.

Thanks, both for all the information, and also the direction to this site.  I shall probably use it in some of my posts in future.
Let me know if you'd like some help.  I'd promise to leave out the IMOs.
We were watching the DVD "The Smartest Guys in the Room" last night. It's a story about the Enron bankruptcy and ensuing fraud investigation.

At one point the movie describes the California energy crisis of 2000, the rolling blackouts. It was just Enron flipping the light switch and raising every Californian's electric bill. The movie includes news footage, with the reporter talking about "the strained electrical grid", who obviously didn't know what was going on.

Bottom line is, the reasons for this outage may not be known for some time, ... for some reason, this reminded me of that event.

The proximate cause of the CA power problesm was

  1. Both Diablo Canyon reactors were down (located at a crucial point due to the undersized "Path 15"  Probelsm appeared when both went down (one scheduled, the other unscheduled).  A week after the reactors came back up, problems disappeared.

  2. Path 15.  At times power from BC & WA was shipped via DC line to Los Angeles and then shipped north to get around Path 15.

  3. Utter and incredible incompetence from Grey Davis (he has a future in FEMA).  Zero $ to renewables for months (which cut their power), whilst paying multiple sides in a bidding war for natural gas, insulating consumers from price signals, etc. etc.

I would have dealt with the problems QUITE differently.

Enron just "played the game" for brutal profit maximization, but so did Los Angeles Water & Power, BC Hydro, etc. with a bit less brutality.

Do not get your facts or history from movies.

Do not be too quick to discount corporate fraud as a cause of this sort of friction either.

Just because you're paranoid doesn't mean someone isn't out to get you.

And just because we're on that 'bumpy plateau' don't think valves can't be closed at an unfortunate time ...

BTW, while watching the movie, I commented that it made Grey Davis look less stupid than he did on TV back during the crisis. ;)

I pulled my solar power patent in 1980 when Reagan took over when he abolished funding for solar power. The amount of money we spent on solar power was so small it was obvious he was doing it for religious reasons.
And in 2000, when I had submitted again, the 2001 Davis administration paid twenty times as much for natural gas power as it paid for solar power from the Luz establishment in the Mojave. So I pulled the patent again!
With peak natural gas in the past, now I am putting it in again. I'll keep it in this time because we are going to need it, and no matter how much they hate solar power they are going to need mine too much for the Federal Government to refuse to license me the areas of the desert I need, and they will pay me for the patent because I'm not going to build one till someone pays for it with a long term purchase contract. Since the patent runs twenty years I can afford to wait.
Also, Australia is also starting to run a little short of natural gas in the east (not in the west) and could use a little peaking power to add to the Snowy. Italy and Spain are getting nervous about relying on Russian natural gas. Most other countries don't pay for patents so I don't include them as customers. Dubai for instance is burning natural gas that they could sell if I thought that they would pay me. Ditto the rest of the Gulf and MENA in general.