Abstract

During the operation of gas storage caverns in rock salt mass the internal pressure changes during filling and withdrawal phases. Additionally temperature variations occur versus operation time. During withdrawal phases the temperature decreases which can lead to stress states in tensile regions at the cavern wall. Because the tensile strength of rock salt is relatively low compared to its compressive strength it is likely that tensile stresses lead to discrete fractures orthogonal to the direction of the tensile stresses.

If fractures of this kind are created - whether vertical or horizontal - the gas will penetrate into the fracture at the relevant pressure and further extend the length of the fractures under certain circumstances. There are currently no theoretical approaches describing the manner in which the fractures might propagate into the not by temperature changes influenced rock salt mass during repeated cyclic pressure changes. This aspect is topic of prospective research.

Salt caverns cannot be entered but only explored by sonar measurements, with which it is not possible to detect tensile fractures at the cavern wall. Within this paper examples from mining configurations will be shown where temperature changes lead to tensile fractures in the surrounding rock salt. These fractures have been well mapped while the temperature development is well documented.

The paper deals with recalculations under consideration of different salt properties of the temperature distributions and the resulting stress state in the surrounding rock salt mass. The stress calculation results and the consequences for the dimensioning of natural gas caverns are going to be discussed and assessed.

1. Introduction

The demands on the dimensioning of gas storage caverns in rock salt have changed considerably in recent years. The operating procedure of injection and withdrawal was influenced mostly seasonal. This meant a high gas inventory in the summer and therefore a high maximum internal cavern pressure, the gas withdrawal in autumn and winter and refilling the gas in the spring and summer, when gas was less needed [1, 2]. Within this phase relatively low operation rates were observed.

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