For the past 20 years almost all new storage plants in Finland, Norway and Sweden installed for crude oil and refined products have been constructed in mined, unlined caverns. This has proved to be the cheapest and safest way. However, the promotion of this technology in other countries has been more complicated than expected. Many obstacles have appeared e.g. less favorable geophysical conditions, fears about environmental damage, laws etc. not related to underground storage. Another major obstacle is the present uncertain state of the petroleum world market. The various obstacles we have encountered are discussed in this paper.
The method of storing crude oil and refined products in mined, unlined caverns is, in Finland, Norway and Sweden, the cheapest and safest way provided that the quantities are not too small. This is confirmed by the fact that during the two last decades nearly all new storage facilities - both commercial and strategic - have been constructed underground. More than 100 plants with a total storage capacity of more than 25 million cubic meters (160 million barrels) have been completed. With this experience and knowledge of all the advantages, considerable efforts have been made to introduce this technology in several other countries. But what was simple and easy in the three countries mentioned above has proved to be more complicated and has taken much longer than expected. We are surprised and somewhat disappointed that this technique has not been generally accepted in other countries and we have difficulties in understanding the reasons for this. Based on the experience of several pre-investigations and feasibility studies executed in South and Central Europe, North America, Africa and Asia the different causes of the obstacles met with are discussed here.
The geophysical conditions in our countries are in general favorable for subsurface constructions. Most of the bedrock consists of very competent granite or gneiss. Decomposed and weathered rock was removed during the last big ice age which means that it is easy to reach the bedrock without any major excavation of overburden. However, it should not be assumed that all rock in these countries is of good quality; now and then we also encounter bad rock conditions. Special methods and equipment have been developed to be used in such cases and the projects can still be completed on a sound economic basis for the owner. The ground water situation is also favorable and it is usually easy to find a stable groundwater table, the level of which is secured and proved by proximity to the sea or lakes. The lack of active seismic zones is also important. It is quite obvious that it is not possible to find places all over the world with this favorable combination of conditions. However, there are several places with similar, good conditions in many areas of the world. Simple estimates also show that there are considerable economic advantages to be gained in constructing storage facilities even in less favorable rock masses; such plants are still able to compete on an economic basis with steel tank storage systems.