MATSUKI Koji Graduate School of Eng., Tohoku Univ., Professor, 大学院・工学研究科, 教授 (10108475)
SAKAGUCHI Kiyotoshi Graduate School of Eng., Tohoku Univ., Assistant, 大学院・工学研究科, 助手 (50261590)
OKUMURA Kiyohiko Graduate School of Eng., Tohoku Univ., Assistant, 大学院・工学研究科, 助手 (40177184)
|Budget Amount *help
¥5,900,000 (Direct Cost : ¥5,900,000)
Fiscal Year 1999 : ¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 1998 : ¥2,800,000 (Direct Cost : ¥2,800,000)
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 study, a hot wire with diameter, d=80, 50 or 30μm and length=50mm was inlaid in the center of the surface of the substrate (elastic silicon gum plate of 40mm×90mm×10mm) used as a reference material. Three K-thermocouples, TィイD20ィエD2, TィイD21ィエD2 and TィイD22ィエD2 of diameter d[μm] were inlaid at xィイD20ィエD2, xィイD21ィエD2 and xィイD22ィエD2[mm] from center of the hot-wire, respectively, in the surface. Temperature rise ΔθィイD20ィエD2
at xィイD20ィエD2, and the temperature difference ΔθィイD212ィエD2=(θィイD21ィエD2)-θィイD22ィエD2) between θィイD21ィエD2 at xィイD21ィエD2 and θィイD22ィエD2 at xィイD22ィエD2 against logarithmic time ln(t) and 1/(t), respectively, were used in calculation of the thermal conductivity, λィイD2sィエD2, and the thermal diffusivity, αィイD2sィエD2, respectively. Originally this method is applied for flat boundary surface of half infinite body of the sample whose thermal conductivity is λィイD2FSィエD2 (=λィイD2sィエD2).
In the study, 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, λィイD2RィエD2, to the sample thermal conductivity of the rocks in situ, λィイD2sィエD2, on measurement values for curved boundary surface of the borehole, λィイD2csィエD2, was studied to evaluate the values of λィイD2sィエD2. Model boreholes from 66 to 120mm in diameter were drilled in each several blocks of rocks having different values of λィイD2sィエD2. Six types of sensors inlaying the hot-wire and the thermocouples having different diameters, d[μm] of 80, 50 and 30 were used. The inlaid positions of xィイD20ィエD2, xィイD21ィエD2 and xィイD22ィエD2 were fixed at 0.5, 2.0 and 4.0 mm, respectively.
As the results, suitable design parameters were obtained in order to evaluate the thermal conductivity, λィイD2FSィエD2. If the measured λ-values on the curved boundary surface in the borehole drilled into the subsurface material having λィイD2FSィエD2 were λィイD2CSィエD2, the ratio of (λィイD2CSィエD2/λィイD2FSィエD2) were less than +10% for the ratios larger than D/d=2400, and less than +5% for the ratios larger than D/d=3000, respectively, without dependency of the ratio of (λィイD2SィエD2/λィイD2RィエD2). Probes of prototype No.1 of which substrates were made by synthetic rubber for boreholes having diameter D=116 to 120mm were designed. The substrates are pressurized by compressed air or hydraulic oil, after the probes have been inserted into the borehole. Less