| Abstract |
Thermophysical properties of deep reservoir rocks should be directly obtained by a measurement technique in situ, because their values by laboratory measurements using samples might be influenced due to the intracrystalline microcracks originating from a stress released from the core during the drilling. The authors have developed a new method and system for simultaneous measurements of the thermal conductivity, the thermal diffusivity, and the specific heat of rocks in situ at temperatures from 273 to 473K, by applying the transient, hot-wire comparative method. In this paper, a hot wire with diameter, d=80, 50 or 30É m and length=50mm was inlaid in the center of the surface of the substrate(elastic silicon gum plate of 40mmÅ~90mmÅ~10mm) used as a reference material. Three K-thermocouples, T0, T1 and T2 of diameter d[É m] were inlaid at x0, x1 and x2[mm] from center of the hot-wire, respectively, in the surface. Temperature rise Å¢É?0 at x0, and the temperature difference Å¢É?12=(É?1-É?2) between É?1 at x1 and É?2 at x2 against logarithmic time ln(t) and 1/(t), respectively, were used in calculation of the thermal conductivity, É…s, and the thermal diffusivity, ÉøS ,respectively. Originally this method is applied for flat boundary surface of half infinite body of the sample whose thermal conductivity is É…FS(=É…S). In this paper, the effect of a ratio of the curvature radius of a borehole, R[mm]=D/2 (D:diameter) to the radius of the hot wire, r=d/2, and the ratio to the reference thermal conductivity of the substrate, É…R, to the sample thermal conductivity of the rocks in situ, É…S, on measurement values for curved boundary surface of the borehole, É… CS, was studied to evaluate the values of É…S. Model boreholes from 66 to 120mm in diameter were drilled in each several blocks of rocks having different values of É…S. Six types of sensors inlaying the hot-wire and the thermocouples having different diameters, d[É m] of 80, 50 and 30 were used. The inlaid positions of x0, x1 and x2 were fixed at 0.5, 2.0 and 4.0mm, respectively. As the results, suitable design parameters were obtained in order to evaluate the thermal conductivity, É…FS. If the measured É…-values on the curved boundary surface in the borehole drilled into the subsurface material having É…FS were É…CS, the ratio of (É…CS/É…FS) were less than +10Åì for the ratios larger than D/d=2400, and less than +5Åì for the ratios larger than D/d= 3000, respectively, without dependency of the ratio of (É… S /É… R). |