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Keeping the Cook Inlet gas flowing Enstar looks at how it will deliver supplies from gas fields and storage next winter as field production continues to decline Alan Bailey Petroleum News
Following a winter of tight gas supplies, alleviated somewhat by moderate temperatures in January and February, the Southcentral Alaska gas and power utilities are assessing how they might route gas to consumers next winter, as gas supplies from the Cook Inlet basin continue to decline. Despite some signs of optimism about the short-term gas supply situation as Cook Inlet newcomer Hilcorp Alaska kicks into gear an aggressive development strategy for the oil and gas fields it has acquired in the basin, much concern remains about the adequacy of the gas supply system to support peak demand during cold winter days.
Deliverability An immediate worry is the need for adequate gas deliverability, in other words the requirement to be able to shift gas quickly enough from gas wells to gas consumers when dropping temperatures elevate gas consumption.
Just 15 years ago, with substantial volumes of gas going to now-mothballed liquefied natural gas and fertilizer plants on the Kenai Peninsula, the Cook Inlet gas fields could deliver about 800 million cubic feet per day of gas into the Southcentral Alaska gas pipeline network, John Lau, director of engineering for Enstar Natural Gas Co., the main Southcentral gas utility, told the Anchorage Mayor’s Energy Task Force on May 1. With a production capability perhaps double the peak winter daily utility gas demand, the producers could easily adjust their production arrangements to meet the Southcentral utilities’ needs, Lau explained.
But with daily gas production having since declined by well over half, to a level below likely peak demand during cold winter weather, the use of gas stored during the summer for winter use has become essential. And the gas producers and utilities have to figure out how to flow gas around the Cook Inlet gas transmission network, to make the gas available at required delivery rates at a variety of points on the system, such as gas-fired power stations, businesses and buildings.
During the winter that has just ended the new gas storage facility operated by Cook Inlet Natural Gas Storage Alaska, or CINGSA, near the city of Kenai, performed a vital role in filling the shortfall in the delivery of winter utility gas from aging gas fields operating at full throttle. And with field production continuing to drop, the utilities have been looking at gas delivery options for different weather scenarios in the winter of 2013 to 2014, with CINGSA’s role becoming ever more prominent.
Winter scenario Lau described one scenario, a somewhat cold day with temperatures in the range of perhaps zero to 10 degrees F that might cause a total gas Southcentral gas demand of about 350 million cubic feet per day. At that demand level, all of the Cook Inlet gas fields would be in full production, delivering in total some 300 million cubic feet per day of gas, with CINGSA plugging a deliverability shortfall of perhaps a little less than 50 million cubic feet per day, Lau said.
A string of gas fields on the east side of the Cook Inlet, including the large North Cook Inlet, Kenai and Ninilchik fields, would contribute about 180 million cubic feet per day of the gas. On the west side of the Cook Inlet, some 30 million cubic feet per day would come from the offshore Steelhead platform, while 74 million cubic feet per day would flow from the Beluga River field. Some small fields and a producer-operated gas storage facility on the west side of the inlet would contribute about 12 million cubic feet per day, while west-side gas fields operated by Aurora Gas would likely contribute about 5 million cubic feet per day.
Gas required for heating buildings in Anchorage, at 165 million cubic feet per day, would dominate the demand side of the gas delivery equation. Space heating in Wasilla and Palmer would add another 40 million cubic feet per day of demand. The other big demand factor would be gas used in gas-fired power stations, with Chugach Electric Association needing 80 million cubic feet per day and Municipal Light and Power needing 30 million cubic feet per day. On the Kenai Peninsula, gas for a Tesoro oil refinery, for power generation and for space heating and fuel would together create a demand for about 30 million cubic feet per day. Aurora Gas’s 5 million cubic feet per day of production would entirely be used to manufacture liquefied natural gas for shipment to Fairbanks, Lau said.
Gas from east and west Under this scenario, some gas from the east side of the inlet and from CINGSA would meet the Kenai Peninsula gas demand, with the preponderance of gas from these sources flowing north to Anchorage at the rate of 194 million cubic feet per day through twin gas transmission pipelines operated by Enstar. These lines pass up through the northern part of the Kenai Peninsula and under Turnagain Arm into Anchorage. The remaining 46 million cubic feet per day that Anchorage would need for heating and power generation, plus the 40 million cubic feet per day needed to heat buildings in Wasilla and Palmer, would flow from the west side of Cook Inlet through an Enstar 20-inch gas transmission line that runs from near the Beluga River gas field north into the Matanuska-Susitna Valley, Lau said.
There is another major gas transmission pipeline system, the Cook Inlet Gas Gathering System, known as CIGGS, that runs under Cook Inlet, connecting the gas pipeline infrastructure on both sides of the inlet. Consisting of a pair of high-pressure lines, CIGGS was originally designed to carry gas from the west side of the inlet to industrial facilities on the east side. The installation in 2011 of a new gas compressor at a major pipeline junction at the eastern end of CIGGS now allows gas to flow east to west through CIGGS, thus providing an alternative route for gas from the east side of the inlet to reach the Matanuska-Susitna Valley and Anchorage.
Severe cold Under the moderately cold winter day scenario it would not be necessary to flow any gas through CIGGS, other than to perhaps meet the specific needs of individual gas supply contracts, Lau explained. But assume an air temperature down to perhaps minus 20 degrees F, a temperature that can occur in a severe Southcentral cold snap, and the delivery situation changes significantly.
Under this “severely cold” scenario, with all of the gas fields already producing at full capacity, output from the CINGSA storage facility would have to ramp up to some 124 million cubic feet per day to keep up with a total daily demand that could reach 425 million cubic feet. That would push the gas flow through the Enstar lines to Anchorage across the Kenai Peninsula to their current maximum capacity of about 230 million cubic feet per day. But, with that maximum flow rate into Anchorage unable to meet the city’s increase in demand, it would be necessary to flow about 24 million cubic feet east to west through CIGGS, with that gas flowing to the Matanuska-Susitna Valley and Anchorage through Enstar’s transmission line on the west side of the inlet.
Lau cautioned that, with the gas pressure in the CINGSA storage facility dropping during the winter as gas is drawn from the facility, the level of output from CINGSA assumed in this scenario would likely only be realistic in the relatively early part of the winter season.
Lack of redundancy And, with the Enstar pipeline through the Kenai Peninsula running close to full capacity, the utilities are concerned about the possible ramifications of some kind of failure in the pipeline system. The new compressor that can push gas east to west through CIGGS is modest in size, only enabling a maximum east to west throughput of 50 million to 60 million cubic feet per day, a factor that results in a throughput bottleneck when moving gas north via the west side of the inlet from the Kenai Peninsula. This constraint, creating a lack of redundancy in the gas delivery arrangements, could be alleviated by the installation of a larger CIGGS compressor, an upgrade that might cost $10 million to $15 million but that would allow gas to flow east to west at up to perhaps 200 million cubic feet per day, Lau said.
The gas transmission lines on the west side of the inlet have plenty of spare capacity to handle that extra CIGGS throughput because gas field production on the west side of the inlet has declined significantly since the transmission lines were built, he said
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