Creep Modeling and Influencing Factor Analysis of Ultradeep Salt Cavern Gas Storage

Underground salt caverns represent optimal sites for the storage of fossil fuels and high-level radioactive nuclear waste. Nevertheless, during the construction and operational phases of salt cavern gas storage, the pressure differential between the cavity's interior and exterior induces continuous creep deformation and contraction of the surrounding salt rock, which may compromise structural stability and lead to collapse. Consequently, the development of a constitutive creep model for salt rock cavities and the investigation of their creep mechanical behavior are essential to ensure the safe operation of subterranean gas storage systems. This study examines a superdeep salt cavern gas storage facility situated in Ningjin, Hebei Province, China, at an approximate depth of 2900 m. Employing complex function theory in combination with viscoelastic principles, a Burgers creep model tailored to the salt rock cavity is formulated. Model parameters are subsequently calibrated and validated through inversion using field data, including pressure monitoring records after wellhead closure and brine overflow rates upon wellhead reopening. The findings reveal strong concordance between theoretical predictions and empirical observations, thereby confirming the model's reliability. The validated creep model is then utilized to qualitatively assess the characteristics of cavity creep and contraction under various influencing factors. Moreover, by integrating prior high-temperature creep test results obtained from laboratory experiments, the study offers a comprehensive analysis of the creep mechanisms governing the surrounding rock in salt cavern gas storage facilities under the combined effects of elevated temperature and pressure in deep strata. This research delivers critical empirical data and theoretical insights that underpin the design, construction, and operational management of superdeep salt cavern gas storage infrastructures.