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ANGDA issues gas storage report Study identifies six potential sites that could support the base gas load and four sites that could support peak loads Alan Bailey Petroleum News
To those with a half-empty view of the world, the steadily depleting gas fields of Cook Inlet present an obvious problem in a region where gas demand and supply are coming into balance. But for people looking to make opportunity out of predicament, some of those legacy fields could perhaps larder excess summer gas for use when demand soars during the winter.
A team from Science Applications International Corp. has completed a study for the Alaska Natural Gas Development Authority into potential gas storage locations around the Cook Inlet region. With winter gas demand running at about 1.75 times the annual average demand, gas storage is already coming into play to bolster winter gas delivery, the report says.
Spur line The report assumes that a spur pipeline to deliver gas into Southcentral Alaska from a future North Slope gas pipeline will be operational in 2020. And if no new gas sources come online meantime in the Cook Inlet region, estimates of future gas demand point to the need for an initial spur line capacity of 300 million cubic feet per day, expandable in stages to 450 million cubic feet per day by 2040.
But gas storage will be needed to smooth out the rate of gas supply across the seasonal peaks and troughs in gas demand, balancing a constant spur line capacity with the seasonal demand.
“The minimum gas storage based on future estimated demand ranges from 11.1 billion cubic feet in 2020 to 15.7 billion cubic feet in 2040,” the study report says. And, because relying on storage capacity at the bottom end of that range poses too much supply disruption risk, the analysts used a safety factor of 1.5 times the minimum demand figures.
“Use of the 1.5 safety factor results in estimated gas storage requirements of 16.7 billion cubic feet in 2020 increasing to 23.5 billion cubic feet in 2040,” the report says.
Delivery rates Some combination of gas reservoir facilities must be able to deliver gas from these stored volumes at rates appropriate to base winter loads and to meet peak demand on the coldest winter days. The analysts estimated the need for base load withdrawal rates ranging from 120 million cubic feet per day in 2020 to 169 million cubic feet per day in 2040. The peak deliverability rate would increase to a minimum of about 80 million cubic feet per day above the base rate.
A number of Cook Inlet gas fields might become available for gas storage at the time when a gas spur line comes on line. But the analysts eliminated from consideration offshore gas fields, because of the likely impracticality of using these fields for storage. Fields south of the Kenai gas field were also eliminated, because of the distances of these fields from market.
And some fields or gas pools appeared too small to provide adequate storage capacity.
That left six gas fields with 16 gas pools as potential gas storage candidates.
The analysts ranked these candidate fields and pools using a number of criteria, such as the reservoir volume, the reservoir quality and the likely depletion date of existing gas in the pool. In doing this evaluation, it turned out that some pools were actually too large for conversion into storage facilities —to maintain adequate reservoir pressure for delivery into a pipeline these would require excessively large permanent volumes of stored gas.
Six for base load That left six pools as possibilities for storing base load gas. In order of suitability, these are:
1. Swanson River — Sterling pool;
2. Beaver Creek — Beluga pool;
3. Ivan River field;
4. Kenai — Sterling No. 5.2 pool;
5. Swanson River — Tyonek pool; and
6. Beaver Creek — Sterling pool.
And, although each of these candidate pools appears to have adequate storage capacity for the base load, none individually would be able to deliver gas at the required rate. However, some combination of the candidate pools should be capable of meeting both the storage and deliverability requirements, the report says.
Four pools candidates for peak storage Four smaller gas pools appeared to be viable candidates for peak load storage:
1. Lewis River undefined pool;
2. Sterling Beluga undefined pool;
3. Lone Creek undefined pool; and
4. Beaver Creek Tyonek undefined pool.
The report also says that using a combination of several pools for base storage “may negate the need for separate peak load storage, at least for the initial years of the pipeline’s existence.”
The analysts estimated a cost of $8.1 million per billion cubic feet of available stored gas for a Cook Inlet region storage facility. That compares with Federal Energy Regulatory Commission figures of $5 million to $6 million per billion cubic feet for a similar type of storage facility in the Lower 48.
“The economic evaluation of Cook Inlet gas storage is expected to be different, most likely higher cost, than Lower 48 gas storage because of the inability to purchase gas at low prices in the summer for storage and sell it at higher prices in the winter season, and (because of) the more remote and higher cost environment in the Cook Inlet” the report says.
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