Abstract: Radial Jet Drilling (RJD),which can drill one or more radial laterals in a vertical wellbore using hydraulic jet to enhance the contact area with reservoirs and create high-conductivity flow channels,is an efficient way of increasing the production,injection and ultimate recovery of an oil field.Its key techniques include the jet drilling ability,computation of hydraulic parameters,self-propelling of the jet bit and borehole extension,measurement and control of well trajectory,etc.A series of in-depth and thorough studies was carried out targeting the above key techniques.Then the fundamental principles of the various jet bits applied in radial horizontal drilling were analyzed,and then the model for jet flow rock-breaking specific energy was set up,while the analysis showed that the rotary porous jet bits had the best rock-breaking effects.With that information,a model for computing the pressure loss of the radial jet drilling system was built,with which,the circulating pressure loss of the coiled tubing with various diameters was analyzed together with impacts of the relevant parameters on the system pressure loss with the goal of identifying the ideal supports for the design of hydraulic parameters.The models for computing the self-propelling force of the rotary porous jet bits and the maximum extension of the radial horizontal wells were established,with which,the maximum extension of the radial boreholes under various operation conditions were analyzed to facilitate the optimization of the equipment and design of the radial boreholes.Finally,a mechanism and method of radial borehole trajectory measurement with Micro-Electro-Mechanical Systems Inertial Measurement Unit (MEMS-IMU) were surveyed to provide a feasible approach for measuring radial borehole trajectories.The research in the paper can lay the foundation for promoting and applying the radial jet drilling technologies.