Natural gases represent the energy that can be stored in large quantities, in the same state as that in which it is used to the final consumer, without being subject to transformations and disruption. One of the fundamental problems of gas industry is taking over the peaks of hourly and seasonal consumption, caused by the random nature of the gas demand, depending on the nature of the industrial consumers (with a relative constant gas demand) and those non-industrial (mainly household consumers with large hourly and seasonal fluctuations) and the possibilities of import, with approximately uniform and limited capabilities, in the period of day or all of the cold season.
The underground storage of natural gas represents a solution for gas supply of consumers in the case of damages to the pipelines, and the coverage of the peaks of consumption in cold season. Compensations for the required gas flows for heating are doing by transferring from the fields with a high dynamic potential in underground storage near the big consumers.
The construction of the cavern in the saline deposits in view of the underground natural gas storage shall be made by the deep wells with direct or indirect circulation. By direct circulation, freshwater is injected through the working space with the smallest diameter, and the brine is evacuated in the annular space. The advantages of this method are: (1) eliminates the danger of dissolution of the salt from the surrounding area of the shaker of the last column cemented, due to the near-saturation concentration of ascended brine; (2) reducing the consumption of the insulating fluid given the lower cross-sectional diameter of the cavern ceiling; (3) performing a cavern of ovoid elongated shape with a maximum cross-sectional diameter at the base. By reverse circulation, freshwater is pumped in the annular space between the two casings, and the brine is evacuated in the casing with the smallest diameter. The advantage of this method is development of high ascending speeds in the inside of the casing with a small diameter, ensuring an efficient evacuation of insoluble material which will be deposited at the cavern bottom.
The underground gas storage in the saline deposits has the following advantages: (1) the large area of salt bodies spreading on the Earth; (2) the duration of the production process is few weeks, being possible to carry out several cycles per year; (3) the operating costs are lower than in the depleted reservoirs or aquifers.
In the paper, the authors review some aspects regarding the underground storage of natural gas in the saline deposits in terms of selection criteria of salt cavern, designing, drilling technology, factors of stability, salt cavern deformation, production behavior.