ABSTRACT

A new concept of storing LNG underground in lined rock cavern, has been developed and tested for several years. In order to prove technical feasibility of the developed concept, a pilot plant has been constructed and tested since 2003 by storing LN2 (Liquefied Nitrogen). This paper presents monitored responses of in-situ rock mass under very low temperatures from the pilot cavern including heat transfer, deformation and thermal stress evolution of rock and rock joints. It is found from the experience of pilot cavern that thermal response of rock in full-scale storage can be predicted accurately. Thermomechanical responses of rock mass also show favorable direction of deformation by cooling in terms of cavern stability.

INTRODUCTION

Many attempts have been made to store LNG (Boiling Temperature: - 162°C) in unlined rock caverns but were not successful. The failures were due to thermal stresses generating cracks in the host rock and the thermal cracks contributed to deteriorating the operational efficiency of the cavern because of induced gas leakage and increased heat flux between ground and storage (Dalstrorn 1992, Glarnheden & Lindblom 2002).

To provide a safe and cost-effective solution, a new Concept of storing LNG in a lined hard rock cavern (LRC) has been developed and tested for several years (Amantini et al. 2004). The concept consists of protecting the host rock against the extremely low temperature by using a containment system with gas-tight steel liner and insulation panels as illustrated in Figure 1.

Groundwater in rock mass around the cavern has to be fully drained during the early stage of the storage operation, before the surrounding rock is frozen, to avoid possible adverse effects of hydrostatic pres- Sure acting against the containment system, and then the rock mass should be resaturated to form an impervious ring of ice, which acts as a secondary barrier against any possible leakage (Fig. 1). In order to verify the technical feasibility of such storage concept, a pilot plant was constructed in 2003 and has been under operation by storing LN2 (Boiling Temperature: -196°C) since January 2004.

This paper presents rock mass responses under very low temperatures from the operation of the pilot cavern including heat transfer, deformation

(Figure in full paper)

OVERVIEW OF THE PILOT CAVERN
Daejeon pilot cavern/or LNG storage

The pilot cavern is located in Daejeon, about 200km south from Seoul, in an existing research cavern implemented within the KIGAM (Korea Institute for Geology And Mineral resources) research facilities. Rock type around the cavern mainly consists of fresh granite with RQD of 80–86 and with the most frequent Q value of 12.5.

Access to the pilot cavern is provided through an existing horizontal tunnel and the cavern roof lies at a depth of about 20m below the ground. Thickness of PU insulation panel is 10cm, and reinforced concrete barriers of 20cm thickness were formed between the rock and the containment system. South concrete wall is exposed to the entrance tunnel, which is not a typical case for full-scale facilities.

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