Four dimensionless parameters, l/D0, (Ts-Tw)/Tw, (Pt2+Pw2)0.5/σ and aw/as which are related to drilling depth, rock and mud jet temperatures, forces loaded to the rock and the rock strengths, and the rock and the mud thermal properties, respectively, are adopted in this study. The parameters were obtained from dimensional analysis. Also, a few model experiment were carried out using a relatively low velocity pure water jet and imitation hot dry rock specimens made of castable fireresistant material. The jet velocity used was 98m/s at nozzle exit and the nozzle diameter, D0, equals 1.4mm. Temperature of the specimens tested were about 15, 200, 400, 600, 800, 1, 000 and 1, 140°. Dimensionless standoff distance was kept constant at 28.6. Jet operation time was fixed at 10s. A correlation equation between l/D0 and the other parameters described above was developed from the multivariate analysis and the experimental data: l/D0=4541(Ts-Tw/Tw)-0.3914(√Pt2+Pw2/σ)-0.9750(aw/as)4.414
Oil and geothermal fluids development technologies require detailed information on the dependence of the thermal properties of formations on temperature, pressure, moisture and mineralogy up to the depth of the order of several kilometers. Temperature dependence of the thermal conductivity of 18 dried core samples from U-1 Well having 1100m in depth at the typical hydrothermal reservoir site in Onikobe geothermal area in Miyagi prefecture were studied in the temperature range from 20 to 500°C. The thermal conductivity was measured by the needle prove method at atmospheric pressure under the controlled temperature conditions. The thermal conductivity of the dry core samples, λea, exhibited aθ+b, b and ce-dθ dependence on temperature, θ, macroscopically (where, a, b, c and d>0 are constants). In situ conduction heat flows at the depths from 150 to 1100m were estimated by the above thermal conductivity data and the temperature logging data. The estimated results offered useful information on the geothermal fluid reservoirs through the U-1 Well.