Stability Evaluation of the Constructed Salt Cavities of Jintan Gas Storage in China

ABSTRACT Learning from the operation experience of built salt cavern gas storages is necessary for new cavity construction. Jintan Gas Storage is the first salt cavern underground gas storage in China and Asia. Since the pilot experiment in 2003, it has been put into operation for about 20 years, with over 29 caverns built and a working gas volume of 800 million cubic meters formed. Due to the complexity of geological conditions and lack of building experience, the shape of some constructed salt cavities is irregular or even deformed, facing stability risks. Based on the geological information and sonar data, the geomechanical model of every constructed cavity is established to evaluate its stability and the possibility of expanding the operating pressure. According to the cavern shape from sonar measurement, all built cavities are divided into three types of trapezoidal roof, large flat roof and abnormal roof. The simulation results and sonar measuring data of different time show that the cavity with a large flat top is the most unstable, and this kind of cavity has a roof collapse with a displacement of 2-8m. The trapezoidal roof cavity is the most stable and has the largest volume, while the abnormal roof cavity has a larger range of plastic damage around the cavity, and the most serious waste in the use of salt rock resources. In addition, based on the stability assessment, the operating pressure of trapezoidal cavity can be appropriately expanded by 1-2MPa, while the minimum pressure of large flat roof cavity should be appropriately enhanced, and the gas production rate should be reduced to maintain the stability of the gas storage. This study can provide guidance for the construction of other salt cavern gas storages. INTRODUCTION With the rapid development of economy and the fast growth of natural gas demand, underground gas storage (UGS), as one of the five links including production, transportation, storage, sale and use in the natural gas chain, is becoming increasingly important (Ding, 2015; Zhang, 2017). As a cost-effective, safe and stable gas storage model at present, salt cavern storage is not only an important facility for natural gas supply, but also a significant guarantee for national energy security (Gabrielli, 2020; Yang, 2022). Most of North America's strategic oil reserves are stored in salt caverns. In recent years, natural gas demand in China has rapidly developed, and salt cavern UGS have entered a golden period of development (Ding, 2023; Gao, 2022).