Distribution of Hyperthermophiles in Kubiki Oil Reservoir in Japan
Yoh TAKAHATA*a, Miyuki NISHIJIMAb, Toshihiro HOAKIc, and Tadashi MARUYAMAa
a Kamaishi laboratories, Marine Biotechnology Institute, 3-75-1 Heita Kamaishi 026, Japan
b Shimizu laboratories, Marine Biotechnology Institute, 1900 Sodeshi Shimizu 424, Japan
c Applied Microbiology section, Biotechnology Reserch depertment of Taisei Co.,Ltd, 3-6-2 Akanehama, Narashino, 275, Japan
Hyperthermophiles have been reported not only from hydrothermal vents and hot springs but also from oil reservoirs. However, their distribution in the oil reservoir is not clear yet. We studied distribution of hyperthermophiles in Kubiki oil reservoir in Niigata prefecture, Japan. The oil layers are divided by many faults and their depths are between 1000 and 1200 m in the ground. Their in situ temperatures were 50- 57℃. Sea water was injected to some wells to enhance oil recovery from 1977 to 1994. This oil reservoir is roughly divided by faults into 3 blocks, KP, OZ and CC blocks. Wells in KP block and in CC block have not been injected with sea water. Wells in OZ block has been injected with sea water.
More than 20 strains were isolated at 85℃ from the formation water in a storage oil tank in December 1995. Characterization and 16S rDNA sequence analysis of the strains showed that the major hyperthermophiles belonged to Thermococcus and Thermotoga. Total cell densities were determined by direct microscopic observation and culturable cell densities of anaerobic heterotrophs were determined by most probable number method at 85, 50 and 20℃. These densities were almost constant from June 1996 to September 1997. Culturable cell densities of Thermococcs spp. and Thermotoga Spp. were 104-105 and 10-1-101 cells/ml, respectively.
To investigate the distribution of these hyperthermophiles and their movement in the oil reservoir, formation waters from oil wellheads and separation tanks were examined. Concentrations of Na+, CI-, Mg2+ and SO42- in OZ block were higher than those in other blocks. This seemed to be caused by sea water injection. Thermotoga spp. were detected only in KP block but their culturable cell densities were very low. On the other hand, Thermococcus spp. were found in all blocks and their culturable cell densities were10°-105 cells/mi. Culturable cell densities of thermophiles growing at 50℃ were 104-105 cells/ml. Cell densities of Thermococcus spp. were about the same to or higher than that of thermophiles. This indicates that thermophiles and hyperthermophiles lived in the same environment at relatively low temperature for hyperthermophiles.
It is considered that formation waters of oil layers do not move from one place to another and the injected sea water did not contaminate the oil layers in other blocks separated by faults. Hyperthermophiles do not seem to spread in the oil layers easily.
We thank Teikoku Oil Co., Ltd. for collection of the formation waters in Kubiki Oil reservoirs. This work was perfomed as a part of the Industrial Science and Technology Frontier Program supported by New Energy and Industrial Technology Development Organization.
