| Conventional drilling method has long drilling cycle in deep formation;however,hydrothermal drilling can effectively increase ROP.Its reactor is the key equipment to realize this method.By numerical simulation and laboratory experiments,hydrothermal reactor structure design,thermal characteristics and thermal cracking of hydrothermal jet are discussed.Results show as follows:The mathematical model of hydrothermal reaction is established,simulation is carried out by varying size of reaction chamber and nozzle,as well as cooling condition.Results show that decreasing the nozzle length can improve the outlet temperature.Temperature potential core becomes larger when increasing nozzle diameter.Structure tests are carried out after simulation.Design of downhole hydrothermal reactor includes multi-channel integration,ESA and reaction chamber.Additionally,bit structure of the reactor is designed to make the borehole regular.Experimental system for hydrothermal jet is developed and experiments are carried out under different reactant ratios,flow rates,jet distances and environment pressures.Results show that temperature potential core is within the 9cm.and increasing flow rate can enlarge the core.Temperature reaches highest within reactant ratio around 0.3.Environment pressure will significantly reduce temperature.Relation between temperature and pressure conforms to Logistic model.Experiment system of thermal cracking is developed and experiments of thermal cracking among six rock types are carried out.Results show that granite has the highest drilling efficiency and cuttings are flake-like.Atmospheric crack temperature of granite and sandstone is obtained.SEM shows micro-pores in shale and evident fractures in limestone.There is no significant difference in composition before and after cracking.Thermal cracking specific energy of granite is 6.1% of high-pressure water jet.Results in this paper could provide guidance for field applications of hydrothermal drilling. |
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