Technical and Risk Evaluation of Underground Gas Storage Construction in Salt Caverns and Its Feasibility in South America
Authors: Jin F. , Xi W. , Chen C. , Shunyuan Z. , Bingshan L. 
Published: May 2017

Abstract
It is economically feasible for none gas producing countries and those that hardly make profits from gas development in the present oil price to import and store natural gas resources. In South America where salt caverns are widely distributed, construction of underground gas storages in depleted salt caverns contributes to both energy strategic reserve security and environment protection with low costs and less land consumed.
The fuzzy mathematics theory and matrix are used to analyze the construction risk and feasibility of underground gas storages. Relevant accidents in China and abroad are classified and studied. The first-order second moment shown performance function that is used to determine the volume convergence failure probability of salt underground storages is established to reveal the relationship between volume convergence failure probability and internal pressure of gas and time. Data of salt mine development in South America are collected to analyze the feasibility of underground gas storage construction in salt caverns.
Several fuzzy sets and fuzzy relational matrixes were established according to the fuzzy mathematics theory, in order to quantitatively compare the feasibility of constructing gas storages in depleted salt caverns and the feasibility of storing gas in removable tanks or underground aquifers. Factors such as overall investment, operation cost, required area, construction period, labor involved, safety, environmental concerns and storage expandibility were all considered. Some underground gas storages in USA or Europe collapsed or were ever faced by gas seepage, cavern shrinkage, surface subsidence or ecological disasters because of abnormal cavern shapes, interlayer collapse, bottom uplift even pillar destruction, etc. Natural gas is injected with high pressure into the cavern and then stored with constant pressure in it. Gas pressure is released when it is collected from underground but the salt cavern keeps running in low pressure eventually. In long-term constant internal pressure and short-term low pressure operation period, the salt cavern's volume convergence failure probability decreases with an increasing internal pressure. Besides, the surrounding rock is more capable of resisting to deformation and rock displacement if the internal gas pressure is improved. Natural gas development costs are relatively high in Bolivia where salt mines are widely found, hence depleted salt caverns shall be utilized to construct underground gas storages.
Underground gas storage construction technologies have not been popular and mature in South America. At present countries such as Bolivia and Columbia are faced with high operation costs of natural gas development. Therefore, it is not suitable to develop natural gas there by large scale now. This article has proposed a feasible plan technically and economically to improve the national strategic energy reserve, reduce natural gas storage costs and realize ecologically sustainable development.