ABSTRACT

Salt rock deposit is considered as a perfect medium for oil and gas underground storage and high level nuclear waste disposal. But the stratification, the distinct deformation between the interlayer and the host rock could be of critical importance for the deformation and stability behaviour of the caverns in the case of bedded rock mass. The creep deformation distinction of the interbed and salt rock surrounding gas storage cavern was represented utilizing numerical creep and interface models. The analysis results demonstrate the stratification effect on the creep deformation figures of the stratified salt rock proving to be strong. The shear deformation distinction between salt rock and the interlayer and, hence, the damage potential are notable when the distinction of the deformation and strength behaviour between salt rock and the interlayer is significant. But an instable and untight tendency of bedded salt rock surrounding gas storage cavern could not be concluded from the analyses since the affected areas are only limited in the vicinity of the cavern.

1 INTRODUCTION

Bedded salt formations are common in China, serving as one important medium for the underground gas and oil storage and disposal of high level nuclear waste (HLW). The projects of ‘West-east gas pipeline’ strongly require gas storage in the nearby regions along the pipelines. The salt formations in Jintan, province Jiangsu, and in Yunying, province Hubei, are selected as host rock for the gas and oil storage, where are different deposition and tectonic history of salt rock, resulting in some differences in depth, lithology and typical geologic structure for the dominant bedded salt intervals. The bedded salt formations are layered and interspersed with non-salt sedimentary materials such as anhydrite, shale, and clay stone. The salt layers themselves often contain significant impurities. The negative influence factors on the gas storage cavern by leaching and operating could be various, but we consider by operating 2 important ones: the layered, heterogeneous lithology and the deferential formation, creep, and probably bedding slip between individual layers.

Most studies on the gas storage have been limited within the pure, homogeneous salt of stocks or domes, and only few have been related to the critical, abovementioned influence aspects. Istvan J.A. et al (1997) have reported a case history of three natural gas storage caverns that were developed specifically for natural gas storage in bedded salt. Coring and rock mechanics studies indicated that the salt could be divided into two distinctive types, one of which could not support an underground excavation. Rock mechanics testing was limited to salt cores, but insoluble ledges and intercalated redbed clay played a great part in the ultimate cavern shapes and spans. On the basis of uniaxial strength testing, cavern instability was anticipated. Because triaxial compression occurs within unmined bedded salt and the strength of the material is very high, hence the cavern is stable. By time dependent tests the author have concluded that tests involving salt do not, generally, exhibit the tertiary creep phase.

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