Numerical study on the flow field of self-propelled multiorifices nozzle jetting bit

Abstract

Ultra-short radius radial jet drilling (USRRJD) is a beneficial method to develop the coal bed methane and conventional oil and gas resources. Jetting bit is a self-propelled nozzle and key tool for USRJD, which could rapidly jet and erode the formation, and then form to regular hole to evaluate oil and gas. Multi-orifice nozzle jetting bit is a special self-propelled bit. This paper introduced flow field characteristics studied by numerical method for multi-orifice nozzle jetting. Combined with the mathematical and RNG k-εturbulent model, physical model is established according the bit shapes and working condition. The simulated self-propelled force coincides well with the reported experimental data. The simulated results show that the flow field includes four regions, such as forward flow, cross flow, backward flow and low velocity. Forward orificesenlarges bottom hole impact zone which is beneficial to enlarge hole diameter, the maximum axial velocity of forward orifices is distanced due to absorb of central orifice.Backward orifices can further enlarge hole diameter and generate self-propelled force. Wall attachment in backward orifices results in low velocity of backward jetting, which would decrease the propelled force. This study provided the reference foroptimizing multi-orifice nozzle and operation parameters.