Problem of predicting the convergence of salt cavern working as natural gas storage is discussed from the theoretical point of view. Two methods of predicting the average annual convergence are compared on a real example of storage cavern. The first is approximate method consisting in extrapolation of stationary convergences calculated for few selected values of natural gas pressure inside the cavern. The second method consists in direct simulation of loading scenario. Calculations were performed for three simple scenarios. Predictions of approximate method are obtained and compared with direct scenario simulations for few-years periods of cavern exploitation. It was possible due to updating of the programs modelling rock massif behaviour by adding the procedures for simulation of multiple-stage loading scenario. Difference between discussed two methods are not big. Differences between average annual convergences for three discussed scenarios are not big also, while local rates of relative convergence significantly vary each other. The results are obtained basing on stationary creeping law with real coefficients. Primary creeping should be included into consideration in the future.