Given the growing demand for gas and oil, natural gas distribution companies have had to generate alternative plans to make natural gas available to meet peak consumption, peak demand, and eventual interruptions during the year. One of these plans consists of using aboveground or subway gas storage units of large capacity and high enough injection and production rates to meet market demands. In addition, subway or above ground gas storage units are a backup option to guarantee continuous flow in unexpected failures or interruptions in the national pipeline system.
Historically, three types of subway natural gas storage units have been used by distribution and production companies primarily in the United States and Europe:
Depleted hydrocarbon reservoirs which are suitable taking advantage that their geological characteristics and fluid properties are already known, in a second level are the adaptations of subway salt formations that, due to their structure, allow confining gas volumes efficiently without appreciable losses, also allow high injection and production rates to be used in short times and at any time; finally, some water reservoirs (aquifers) are also used as natural gas storage units because they have similar geologies to depleted hydrocarbon reservoirs.
Various experts support the reuse of salt caves to store vast quantities of oil. In the United States, new holes are even being constructed in salt mines to build huge renewable energy storage facilities. Facilities with an astronomical capacity of up to 150,000 MWh, i.e., about 150 times more than the total energy storage capacity in Li-Ion batteries used on US soil today.
Salt caverns can store less oil than depleted reservoirs but offer higher injection and gas production rates and thus a higher number of cycles. This type of storage unit is primarily used to supply peak demand. Salt cavern oil storage to be suitable must have sufficient consistency and depth to withstand the required pressures. The gas of base needed is between 20 and 30%. The injection period is between 20 and 40 days, while the production period is 10 to 20 days. The average storage volume used in this type of storage is around 500,000 cubic meters.
Caverns can be created in salt domes by drilling into them and injecting water into the rock, which dissolves the salt. The resulting brine is extracted, leaving a large cavity. The next step is to store oil in the cavern.
The salt cavern oil storage type is made based on design parameters, capacity, and maximum and minimum storage pressure. Therefore, the first operation to be performed to evaluate the mechanical properties of the salt formation is to drill an exploratory well.
The exploratory well is generally used for leaching work. During leaching, the salt cavern oil storage development will be controlled by mathematical models based on seismic testing and exploration.
Once the salt formation is identified, boreholes are drilled, and water is circulated over a salt interval to dissolve it as brine and then inject the gas to be stored.
Flow rates and operating pressures can be designed according to needs, well productivity can be 3 to 4 times the productivity of wells in conventional reservoirs, the possibility of expanding storage capacity by leaching other caverns, low base gas volume for high extraction rates, high level of safety, full recovery of base gas, need for a suitable salt formation, brine disposal problems under certain circumstances.
Taking advantage of these caves to store oil or other is not new, but there was no great need to opt for it. Salt caves cost ten times less than surface storage tanks and 20 times less than traditional rock mines.
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