Design of slurry forward/reverse circulation switching mechanism and optimization of its fluid channel in hydrodynamic-driven cordless coring system

Abstract:

In order to solve the problem of low efficiency of core drilling in ultra-long horizontal holes， a cordless core drilling process is proposed to complete the delivery and recovery of the inner tube assembly by mud hydraulic drive. To this end， this paper designs a positive/reverse circulation switching mechanism for the borehole mud that assists the delivery and recovery of the inner tube. This mechanism can realize the positive/reverse circulation switching by changing the mud flow direction through the mutual cooperation of two dual-channel ball valves. Through the ANSYS software， the L type double channel of the positive/reverse circulation switching mechanism is simulated， and the results show that after the fluid passes through the L type channel， the high-velocity fluid only accounts for 50% of the total amount of fluid， and the pressure drop of the fluid through the ball valve channel is 1008.1Pa， and the fluid near the inside of the channel will produce a lot of turbulence， resulting in different degrees of backflow. For this reason， the shape of the channel was optimized， the original L channel was changed to a circular channel， simulation results show that the fluid through the circular channel， high-speed fluid accounted for 90% of the total amount of fluid through the ball valve channel pressure drop is only 105.3Pa， and the fluid trace overall smooth， only a small amount of fluid reflux occurred. The optimized fluid channel is effective in reducing the pressure drop through the ball valve. The optimized fluid channel effectively reduces the head pressure loss and ensures the stable transportation of the fluid.

Key words:horizontal hole;cordless coring;switching between forward and reverse loops;hydraulic drive;fluid channel optimization;tunnel exploration