Natural gas is primarily stored underground under pressure, utilizing three main types of geological formations, but it can also be stored above ground in specialized tanks.
Here's a breakdown of the most common storage methods:
1. Underground Storage (Most Common):
This method involves injecting natural gas into suitable underground geological formations for later withdrawal. These formations act as large, natural reservoirs.
-
Depleted Oil and Gas Reservoirs: These are the most frequently used type of underground storage. They are already known to hold hydrocarbons and have the necessary geological structure to contain gas. They also offer an existing infrastructure of wells and pipelines, which reduces the cost of conversion for storage.
-
Aquifers: Aquifers are porous and permeable rock formations saturated with water. Natural gas can be injected into these formations, displacing the water and creating a "bubble" of gas. However, aquifer storage is more complex and expensive than using depleted reservoirs because it requires more monitoring and maintenance to ensure the integrity of the gas bubble and prevent contamination of the water supply.
-
Salt Caverns: Salt caverns are created by dissolving salt deposits deep underground. They offer high injection and withdrawal rates, making them suitable for meeting short-term peak demand. Salt is also impermeable to gas, providing a secure containment. They are particularly suitable for managing rapid fluctuations in demand.
2. Above-Ground Storage:
This method is less common for large-scale storage but serves specific purposes.
-
Liquefied Natural Gas (LNG) Tanks: Natural gas is cooled to approximately -260°F (-162°C), converting it into a liquid, which significantly reduces its volume (about 600 times). LNG is stored in specially designed, heavily insulated tanks. This method allows for large volumes of gas to be stored in a relatively small area, making it useful for import/export terminals and peak shaving.
-
Gaseous Storage in Tanks: Natural gas can also be stored in gaseous form in above-ground tanks, typically at high pressure. These tanks are generally smaller in capacity compared to underground storage and LNG tanks and are often used for localized storage or to meet specific operational needs.
Summary Table:
| Storage Method | Description | Advantages | Disadvantages | Common Use Cases |
|---|---|---|---|---|
| Depleted Oil/Gas Reservoirs | Re-purposed oil or gas fields used for storing gas. | Existing infrastructure, known geological properties, large storage capacity. | Can be slower injection/withdrawal rates, potential for residual oil/gas interference. | Seasonal storage, large-scale gas reserves. |
| Aquifers | Underground, water-bearing porous rock formations. | Large storage capacity. | Requires more monitoring, higher initial cost, risk of water contamination. | Seasonal storage, strategic reserves. |
| Salt Caverns | Underground cavities created in salt deposits. | High injection/withdrawal rates, impermeable to gas, rapid response to demand changes. | Smaller storage capacity compared to reservoirs and aquifers, higher initial cost. | Peak shaving, balancing daily demand fluctuations. |
| LNG Tanks | Super-cooled liquid natural gas stored in insulated tanks. | High density, efficient storage for large volumes in small areas, suitable for transportation. | High initial cost, requires specialized equipment, boil-off losses. | Import/export terminals, peak shaving, remote locations. |
| Gaseous Storage Tanks | Compressed natural gas stored in above-ground tanks. | Simple technology, localized storage, can be deployed quickly. | Smaller capacity, higher pressure requirements, potential safety concerns. | Localized storage, small-scale operations, emergency backup. |
In conclusion, natural gas storage is a crucial aspect of the natural gas industry, ensuring a reliable supply to meet fluctuating demand. The chosen storage method depends on various factors, including geological suitability, storage capacity requirements, and operational needs.
