Airlifting & reverse-circulation spoil removal

Removing cuttings from a deep or large-diameter hole is often the real limit on rate of progress, more so than cutterhead power. Airlift and reverse-circulation systems are the standard answer, and they look deceptively simple: blow air into a riser and spoil comes out of the top. In practice they are governed by multiphase flow, downstream resistance and installation geometry and a nominally viable system can stall in service if any of those is wrong. We design and assess airlift spoil-removal systems by modelling that physics, not by rule of thumb.

How an airlift works

An airlift runs on an imbalance of hydrostatic pressure. Picture a U-bend full of water: with no air, the head is equal on both legs and nothing flows. Inject compressed air into the long leg and it lowers the density of the mixture above the injection point, reducing the hydrostatic pressure on that side. The system is now unbalanced, and water rises up the long leg as an aerated mixture, carrying cuttings with it, for as long as the inlet head exceeds the riser head. In a reverse-circulation drill, the water depth provides the driving head, cuttings are drawn into the bit nozzle and the aerated slurry climbs the riser to a separation arrangement on deck.

Airlift performance is governed by a handful of well-defined levers, and we model them explicitly when sizing a system. That modelling, refined against real jobs, is how we size a spread that meets the required rate of progress. Talk to us about your duty.