Experimental Study On Mending Of Instable Borehole Through Melting Glass-ceramic Casing In Geological Drilling

Based on rock melting technology, a novel method for mending Instable borehole wallis developed. It works through a manufactured wall that is built by meltingglass-ceramic casing under700℃. We have breakthroughs in developing an electricheat element and low melting point material. The results of laboratory experiments aresatisfying. It indicates that this technology has great market potential.First, we make a physical model to describe the law of heat transfer on twohypotheses: the heat transfer media are isotropic and the parameters ofthermo-physical properties are constant. On the basis of the law of conservation ofenergy and Fourier’s law of heat conduction, we deduce the differential equation ofheat conduction. The law of temperature drop outside the external surface of heathead agrees with Logarithm. In addition, the actual temperature field accords withEuler’s Number (T=T0eξ). The heat mainly concentrates near the head, which enablesthe mending material to reach its melting point more easily.Furthermore, the heat head consists of heat element of high strength graphite andexternal shell of GH742alloy. The high strength graphite can work under1200℃.Although carbon-carbon composite (C/C) is characterized by high strength and largethermal conductivity, it performs badly in resisting high temperature oxidation. Withhigh strength, large thermal conductivity and strong high temperature oxidation,GH742can basically meet the working requirements.The low melting point material mainly consists of glass. We research the influence ofquartz sand and aluminum (Al) on physical and mechanical properties. We selectglass-ceramic adding20%-30%quartz sand and Al as the final component.Finally, we develop a lab facility consisting of three-phase electric power regulator,frequency converter, split tubular simulator, infrared thermometer, and thermocouple.Using this facility, we conduct a series of experiments and validate the heat head, lowmelting point material, and device for simulation. Additionally, the result pertaining tothe radial temperature distribution basically agrees with the numerical simulation.