Abstract

The idea of storing hydrocarbon products underground for protection was practised already during the first world war. However, only after the development of techniques to achieve full containment in caverns without any wall protection, the underground storage of crude oil, oil products and LPG became commercially attractive in the 1950's. Hundreds of such storage caverns have been constructed in hard rock since that time, predominantly in Scandinavia and in the USA. In later years, several caverns have been constructed in third world countries as well. The basic working principle for unlined rock caverns is the action of groundwater in rock fractures. By maintaining a cavern pressure which is below the groundwater pressure at all points on the cavern periphery, there will be no possibility for the hydrocarbon to migrate into the rock mass. Storing natural gas in rock caverns is a new challenge for rock engineers. Economy here requires that the caverns are designed to accept high gas pressure or low condensate temperature (LNG). Substantial research is underway to clarify rock mechanical, hydrogeological and thermodynamic problems associated with such storage.

Introduction

The subject of hydrocarbon storage is a very appropriate theme for a joint conference with petroleum and rock engineers. A close look at the containment criteria for an excavated rock cavern, storing a hydrocarbon liquid or gas, reveals that these are basically the same as for a natural reservoir.

Like in underground oil and gas reservoirs, containment is achieved in unlined caverns through good host rocks and due to the saturation of these rocks with groundwater at sufficient pressure. Whenever these conditions do not occur, or are inadequate at the site selected, engineered systems must be added such as wall liners, water curtains, freezing and the like.

There has been a strong development of under- ground storage from the days when the rock was solely used for impact protection and steel tanks were used for containment - to today's rock caverns which arc designed to take advantage of the inherent capacity of rock masses to safely contain oil products and gases.

The history of hydrocarbon storage in rock caverns is quite short, less than 50 years, and successful. Very few serious accidents or malfunctions of such caverns are known although several hundreds of them are in operation today.

This paper will review the history and present status of design principles for rock caverns, intended for hydrocarbon storage.

1 THE DEVELOPMENT OF STORAGE CAVERNS FOR OIL AND OIL PRODUCTS

The predominant method of creating bomb-proof storage tanks during the 1940's was steel-concrete lined cylindrical tanks, known as SENTAB tanks. Many of these tanks, constructed with 4-8 mm steel plates on 0,2 - 0,5 m concrete are still in use today. The similarity with modern steel membrane concepts proposed for compressed gas is obvious.

The Swedish inventor H. Jansson proposed already in a 1939 patent that the liner could be omitted, provided the oil is stored below the groundwater.

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