ABSTRACT:

The equation of Mohr-Coulomb salt dilation criterion has been developed obtained from the triaxial compression and extension laboratory tests of bedded salt. Numerical stimulations of the natural gas storage caverns in bedded salt formation are carried out by FLAC3D to evaluate the effect of cavern design parameters on the minimum permitted operating gas pressure necessary to maintain cavern stability. The influences of cavern depth, cavern roof span, roof salt thickness, overlying shale thickness and overlying shale stiffness on the minimum permitted operating pressure are studied. In order to compare the calculating results conveniently, the minimum permitted operating pressure is expressed in terms of a pressure gradient at the casing shoes. The comprehensive study results indicate that the minimum permitted operating pressure gradient has a proportion with cavern roof span, and an inverse proportion with overlying shale stiffness. The roof salt thickness and overlying shale thickness have little or no influence on the minimum permitted operating pressure gradient.

1 INTRODUCTION

In order to overcome the natural gas use-peak and emergency reserves of China eastern provinces, the state decided to construct underground salt caverns, located at eastern of China, to storage natural gas on August 2006. The whole constructions are made up by a total of 16 separate caverns, with a total construction scale of 3.2×108 m3/a working gas. The newly built salt cavern depth, height and diameter are about 1900 m, 90m and 60 m, respectively. The effective space of single gas storage cavern is about 1.5×107 m3, operating pressure about 7∼17MPa. Comparing to the other salt caverns(CHENWeizhong et al, 2009; P. Bérest et al, 2003;Yin Xueyuan, 2006), the newly built salt caverns are much deeper in buried depth, higher operating pressure and more multilaminated non-salt, which make the constructions become more challengeable.

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