Abstract
This study focuses on a safety evaluation method for underground gas storage. Gas storage is usually constructed underground in complex environments, and the service life of such facilities is limited. To ensure the secure and long-term operation of gas storage facilities, safety evaluation has become the focus of management. The present paper provides an effective method for safety evaluation. An index system was established as the foundation of the analysis for this evaluation, and the matter-element extension method was applied to obtain a quantitative evaluation result. For the weight values of each index in the matter-element extension method, this paper presents a comprehensive weight computation method based on vague sets and entropy. By application of this method, the safety level of a gas storage facility in the Jintan salt mines (in Jiangsu, China) was calculated, and the evaluation result was 4.6433, which meant the safety level was V and the underground gas storage was slightly at risk. It indicated that the influence on the overall safety and tightness of this gas storage could be ignored in the operation process, but the frequency of regular monitoring should be increased. The defective indexes were also obtained, such as salt rock cohesion, the roof thickness, the volume contraction ratio, the interlayer content, the height of the casing shoe and the adjacent cavity pressure difference, which need to be monitored and modified. This paper evaluated the safety of the underground gas storage from a unique perspective. It is expected that the results of this research will contribute to the maintenance and operational decisions, and provide a reference for management in the energy industry.
Highlights
The consumption of natural gas may not be constant but fluctuate seasonally, which is not compatible with the extraction process
The objective weight is determined by the entropy method, and the objective weight values are calculated by equations. (2.9) to (3.1).After obtaining the subjective and objective weights, we obtain the comprehensive weights of each index shown in table 6
The subjective weights were obtained by vague set theory, which considered the difference in experts’ preferences and played a guiding role in the weights of the indexes, and the objective weights obtained by the entropy method judged the influence according to the values of the indexes, forming the mathematical basis
Summary
The consumption of natural gas may not be constant but fluctuate seasonally, which is not compatible with the extraction process. The studies on safety are mainly focused on the mechanical properties of the geological storage medium and the establishment of constitutive models; these studies provide a scientific basis for safety evaluation. Based on the elastic–plastic constitutive model, creep damage models have been formed and used to study permeability, damage and self-healing of salt rock that can be used for underground storage [8,9,10,11,12]. The existing studies have mostly focused on the impacts of a single index; until now, there was no unified global standard for safety evaluation of underground gas storage. Combined with the matter-element extension method, the safety level of the underground gas storage was obtained.
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