过去的循环工艺是由冲洗液把岩屑带走,冲洗液直接通过钻头中的水口,不是流向钻杆而是流向钻孔的环状间隙。要改变循环方式时,一般是略微提升钻头,以便让冲洗液越过钻头并通过中央通道回流,把岩心带到地面。这种钻进方法要求很大的泵压,只要流体 In the past, the recycling process was carried away by rinsing fluid, which was passed directly through the nozzle in the drill bit, but not to the drill pipe but to the annular gap of the borehole. To change the circulation method, it is common to slightly raise the drill bit so that the flushing fluid will pass over the drill bit and back through the central channel to bring the core to the surface. This drilling method requires a lot of pumping pressure, as long as the fluid