The paper is concerned with a recent discovery of oil degrading bacteria reducing the effect of a water curtain between two oil storage rock caverns. Attention is drawn to the problem of bacterial growth at the oil/water interface. The importance of establishing water curtains before filling up caverns with oil products is emphasized. Finally, some means of preventing bacterial growth is discussed.
The application of water curtains in order to maintain or obtain a ground water gradient preventing leakage from rock caverns for oil storage, is well known (fig. 1). Furthermore, the occurrence at the oil/water interface of a slimy product - resulting from microbiological activity - has been observed in connection with various storage facilities for oil products. The present paper is concerned with a recent discovery of oil degrading bacteria reducing the effect of a water curtain between two oil storage rock caverns in central Norway. To the author's knowledge, this particular effect of an otherwise well known phenomenon has not previously been published. Attention should however be brought to bear on the phenomenon in view of the economic consequences involved.
The plant in question was constructed during the middle seventies. The local bedrock consists of a fairly massive, plutonic granite intruded into a greenstone complex. A fresh-water curtain was established in 1978, in order to stop a considerable leakage of oil product from one cavern (fixed oil level) into the neighboring one (fluctuating oil level) (fig. 1). These two caverns are used for the storage of two different refined oil products. The water curtain reduced the oil leakage to a minimum. This effect, however, proved to be temporary (fig. 2). After a few months only, an increase in loss of oil product from cavern A was again registered. Besides, the water infiltration was strongly reduced, only one out of six drill holes consuming water. At the end of 1979 it was decided to start cleaning the drill holes of the curtain. This was achieved by means of drilling equipment and high pressure water. The holes proved to be completely filled up with a slimy product, a sample of which was taken to the laboratory for investigation. Samples were also taken of the water in the drill holes and of some mineral material (mud and rock particles). The samples of mineral material and slime were taken as filtrates during the washing out of the holes. On the removal of the slime, the water curtain once more proved to be efficient (fig. 2).
Attention is drawn to fig. 3. In addition to the analysis reported in this figure, examination of mud samples was carried out by means of X-ray diffraction. The mineral composition was found to comply with that of the local bedrock. No trace of swelling clay minerals was found, thus excluding any possibility of such minerals contributing to the sealing of the drill holes. Samples of crushed rock (sand/gravel size) from the drill holes nos. 5 and 6 contained some fragments of calcite, probably originating from joint and fissure fillings.