Environmental Engineering Reference
In-Depth Information
substantial well maintenance and monitoring to prevent working gas from
being lost via wellbore leaks into other permeable reservoirs.
Aquifer Storage
Aquifer storage involves injecting natural gas into underground formations
that are initially filled with water (aquifers). The gas is injected at the top of
the water formation and displaces the water down-structure. These types of
reservoirs account for only 10 to 15% of total U.S. storage deliverability and
exist mainly in the Midwest due to the lack of depleted oil and gas reser-
voirs. Advantages of aquifer reservoirs include:
• Proximity to end users
• High deliverability from a combination of high quality reservoirs
plus water drive during the withdrawal cycle; high deliverability
increases the ability to cycle the working gas volumes more than
once per season.
One disadvantage is a high level of geological risk. These reservoirs have not
previously trapped hydrocarbons and, as a result, a degree of uncertainty
surrounds their ability to contain injected base and working gases. The risk
for substantial reservoir leaks is also present. Because these reservoirs pro-
duce via water drive, water production is often experienced during the with-
drawal cycle, increasing operating costs. Due to the water drive mechanism
during the withdrawal cycle, the base gas requirements are high (80%). A
large percentage of base gas is not recoverable after site abandonment. The
high base gas requirement likely limits the number of new aquifer storage
projects by increasing the initial capital cost (Katz, 1977).
Salt Cavern Storage
Salt cavern storage sites are solution-mined cavities in existing salt domes
and structures (Figure  8.4). These shallow cavities are filled with injected
natural gas and act as high pressure storage vessels—in essence they are
large underground storage tanks for natural gas. Advantages include:
• Low base gas requirement of 25% that can approach 0% in
emergencies.
• Ultra-high deliverability (much higher than depleted reservoir and
aquifer storage).
• Operational flexibility: these reservoirs can cycle working gas four
to five times a year. Their Gulf Coast location allows daily produc-
tion and nightly injection to help meet peaking demands during the
summer air conditioning season.
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