The problem with natural gas feeds, as opposed, for example to electricity, is that when supply is shut-off the flame that burns the gas goes out. Thus there is a safety protocol required to restore service:
The process to restore natural gas service to homes and businesses is the most time-consuming aspect of any outage. We ask for your patience as we begin and complete the restoration process over the upcoming days.
What can our customers expect? The restoration process means visiting each home and business twice. First, every meter is shut off. Then, work begins on restoring gas in the large pipelines bringing natural gas to their area and make sure the system is operating safely. Finally, our crews will go door-to-door, revisiting every home and business, to turn the meters back on, perform critical safety checks and relight gas appliances. There may be a slight smell of gas in your neighborhood while technicians purge the meters.
Who will be relighting my appliance? Qualified, trained New Mexico Gas Company service technicians from around the state will be helping to restore service to affected areas in an orderly manner.
The disruptions are not just confined to New Mexico. El Paso Natural Gas has declared “Force majeure” because of the constraints on supply. And frozen wellheads in Wyoming are reducing the flows available to customers in California. Just as with electric power, the utility answer is to shed some of the industrial load. Large industrial concerns get a lower price for their gas if they agree that it can be shut off in times where supply is no longer adequate. Such is now the case in San Diego where 88 companies have had their supplies curtailed as part of this program. Under normal circumstances the region is supplied through the Trans-western pipeline, which carries 2.4 Bcf/day.
It is reported that up to 5% of normal production has been temporarily lost both due to well head freeze-off and problems in the processing plants. And this is not all occurring in just the more northerly states.
The unexpected drop in supplies from wells freezing off forced utilities and some looking to churn a quick profit to reach for gas in storage, forcing the company to set limits on withdrawals. At least 1.5 bcfd of production is offline in the East Texas, Fort Worth and Texas Gulf Coast basins, Bentek estimates, with at least 900 mmcfd offline in the Anadarko Basin, which lays partly in Texas and Oklahoma. 'Anadarko volumes being off makes a lot of sense,' said Matt Marshall, senior energy analyst with Bentek in Evergreen, Colorado. 'It got hit hard by the weather and it's liquids rich.'While supplies in storage should be more than adequate to meet demand, the problems arise in both getting this into the delivery pipelines, and then getting it to the customer. Or deciding which customer gets it. As the EIA noted in their latest (Feb 3rd) Natural Gas Weekly Update
Liquids-rich gas tends to freeze faster since it has a higher dew point, Marshall said.
The largest percent price increases during the week occurred in markets west of the Mississippi River, where there has been little price volatility this winter.In the Rockies and Midcontinent, where weather conditions were extreme and there were numerous reports of declines in production due to icing conditions at producing wells, price increases exceeded well over $1 per MMBtu or about 30 percent. BENTEK Energy, LLC, reported that flows on pipelines shifted significantly as higher demand in localized markets in the Rockies decreased flows on other pipelines that transport supplies out of the Rockies to the east, such as the Rockies Express Pipeline. In addition, numerous Midcontinent and Rockies area pipelines reported constraints on their systems, resulting in losses of flexibility to move gas between regions . . . . Prices in the Rockies increased at all trading locations. For example, the price for supplies on the Questar Corporation system in Utah increased $1.39 per MMBtu to $5.46, the highest price reported at this location this winter.
(As an aside it is worth noting that the EIA is predicting that there will be an additional 4 Bcf of natural gas coming onto pipelines from the Marcellus shale by this November). Overall the wellhead freeze-offs and other problems lowered national gas production, on average, to around 62 bcf/day.
Wellhead freeze-off occurs because the natural gas coming out of the well contains a varying amount of water in the mix. When temperatures get cold enough then, even though the gas comes out of the ground quite warm, this water can freeze. (A gas is considered dry in the USA when it contains less than 7 lb of water per million scf). When it does it blocks the flow channels, and the well is shut-in until it thaws. That is the simplest case, and since we know the freezing temperature of water then that should tell us when it is going to happen. Unfortunately, as some of you may remember from the Gulf oil spill incident this last summer, there are also conditions when gas hydrates can form in the infrastructure. These can form and freeze at higher temperatures. More typically, however, it is the water vapor in the line which causes a problem. David Fish gives an example of what can happen.
In a practical case you can have gas flowing in the pipeline at 60 degrees Fahrenheit and 700 psi and have no evidence of freezing. If you pass through a regulator station and cut the pressure to 225 psi, the flowing temperature at the point of regulation will drop 33 degrees Fahrenheit to approximately 27 degrees Fahrenheit. If the gas stream is saturated with water vapor and condensate, you will quickly experience the freezing concerns we are discussing.There are several ways in which this the supply can be protected from this happening – though in parts of the country where it doesn’t normally get this cold, they might not be cost effective. The first is to remove the water, which can be done using a variety of tools typically either a solid or liquid dessicant, alternately methanol can be trickled into the line, lowering the freezing temperature of the mix, hopefully below prevailing temperatures, and thirdly the system can be kept warm enough that it doesn’t freeze. The last two of these make some assumptions on how cold it is going to get. And if the temperature falls below that point, then they may become ineffective.