Study on Mechanism of Rock Core Plugging at Bottom of PDC Reverse Circulation Coring Bit for Nearly Horizontal Hole

To reveal the mechanism of rock core plugging in drill bit during hydraulic reverse circulation coring drilling under nearly horizontal condition, the numerical simulation software is used to carry out the numerical simulation for the local flow field of PDC reverse coring bit, then the different number of bottom orifice for PDC coring bit and the effects of internal orifice combination on flow distribution are analyzed, which is verified by the field tests. The results show that when the number of bottom orifices of the bit body is constant, the return flow of the center channel of the bit body increases with the increase of the number of internal orifices; when the number of holes in the bit body is constant, the return flow of the center channel of the bit body increases with the decrease of the number of bottom orifices. Through the comparison of the numerical simulation results for different models, it is determined that when the number of bottom orifices is two and the number of internal orifices is six, the center channel has the reasonable return flow and flow velocity, which can guarantee the smooth migration of rock core to the greatest extent theoretically.