In December 2003 a new CG5 gravimeter was tested at Hirogawara, where a gassy cold geyser is activated primarily by the evolution of carbon dioxide. The CG5 gravimeter has a new capability of raw data acquisition, which enables us to store the unprocessed 6 Hz data (gravity, tilt-x, tilt-y, and internal temperature) in memory. We detected a particular signal not in gravity but in tilt. Continuous gravity record at the geyser constrains the volume and/or the depth of the void, where fluid flow in/out accompanying the geyser activity. This result is of particular interest in field surveys of temporal gravity changes related to some environmental or geodynamical processes, where gravity variations are expected to occur in hours or shorter period. A combination of raw data recording and post-processing is believed to be effective in realizing high precision microgravity monitoring using the CG5 gravimeter.

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In Japan, the annular space between heat exchange pipes and well walls are commonly grouted in ground heat exchangers (GHEs) to avoid the formation collapse and to secure the contact between the heat exchange pipes and the formation. As is frequently applied in northern European countries, however, GHEs can be completed without grouting in case the formation rock is rigid and groundwater level is located near the ground surface. To investigate the applicability of GHEs without grouting in Japan, the evaluation of heat exchange capacity of such GHEs is quite important for the design of optimum GHE length and hence to minimize the initial cost of geothermal heat pump systems.
In this research, an ungrouted GHE was drilled in a hard formation of granite in Fukuoka City, Japan and series of thermal response tests (TRTs) were carried out under various heat loads. On the basis of the chronological changes of heat medium temperatures and vertical temperature profiles measured using an optical fiber thermometer, the thermal resistivity of the GHE and the vertical distribution of thermal conductivity were estimated using graphical and analytical interpretation methods. The results of interpretation indicated the improved (reduced) thermal resistance of the ungrouted GHEs in comparison with grouted GHEs, due to the effect of natural convection of groundwater between the U-tube and the well wall. The interpreted vertical distribution of thermal conductivity showed a good agreement with the results of graphical interpretation, the local geological information and the laboratory measurements of core samples, indicating the reliability of the interpretation method of vertical temperature profiles measured by optical fiber thermometers in ungrouted GHEs.

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Recent studies suggest that a huge biosphere exists deep in the Earth, which people never used to think of for a long time. Study of microbes living in subsurface may help us to find the new chemical reaction caused in earth interior, and a new fact of the origin of life etc. On the other hand, rocks and rock-forming minerals usually contain many closed cracks and fluid inclusions, where ancient fluid may have been trapped and isolated. We then expect that organic matter or microbes may exist in the fluid. In this study, we artificially synthesized pieces of quartz with fluid containing either proteins or thermophiles in closed cracks and fluid inclusions under a relatively low temperature (<99°C). Under uncontaminated conditions, the quartz samples were crushed in distilled water and biological media to extract the fluid containing proteins and microbes, respectively. As a result, we succeeded in detecting the proteins and microbes in the fluid. We therefore conclude that our experimental procedures are valid to detect proteins and/or microbes in ancient fluid isolated in a rock in nature.

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