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/D
0=4541(T
s-T
w/T
w)
-0.3914(√P
t2+P
w2/σ)
-0.9750(a
w/a
s)
4.414
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