reversecirculationborrning

Reverse circulation drilling, or reverse circulation boring, is a drilling method used mainly in mineral exploration to obtain continuous rock samples quickly and with minimal downhole contamination. In this system, compressed air is pumped down the center of the drill string to the bit. The cuttings produced at the bit are carried up the outside of the drill string through the annulus between the drill pipe and the borehole wall and are directed to a surface sampling system, such as a cyclone or sample barrel. The sample is therefore collected in a line separate from the air path, enabling relatively continuous, representative recovery of material.

The technique typically uses a hollow drill pipe with an air line inside the string. The returned cuttings pass through the surface cyclone and are captured for analysis. This configuration is contrasted with conventional mud or water-based drilling, where fluid returns are used to lift material. Reverse circulation drilling is commonly implemented with portable or semi-mobile rigs and is favored for rapid sampling, reduced dust, and cleaner samples suitable for geochemical assays.

Advantages include faster sample turnover, cleaner and more representative cuttings, and reduced reliance on drilling fluids, which lowers contamination risk and water use. It is well suited for near-surface to medium-depth exploration in hard rock environments and for delineating mineral resources.

Limitations include less suitable sampling for fine-grained or clay-rich intervals, potential sample contamination at the surface handling system, and the absence of intact core for structural analysis. Proper equipment setup and sample handling are essential to maintain sample quality.