Directional Drilling Open Pit Dewatering Wells – Great Idea

I read an interesting article in the Mining Magazine May 2015 edition called “Top 10 Technologies”.  One of the new technologies that jumped out at me is the capability to directionally drill open pit dewatering wells.   This is an oil field technology from Schlumberger Water Services that was now going to be applied to mining.

One of my past roles was as a mine engineer on the Diavik diamond mine team. Pit geotechnical and hydrogeology were under my domain during project design and permitting from 1997 to 2000.

The granitic rock mass was geotechnically very competent with a limited amount of jointing and fracturing.  The pits were going to be located within a lake bed.

It was anticipated that groundwater seepage coming from a partly permafrost pit wall could create a host of operational problems in winter. Most of the groundwater flows were predicted to be along a few major structures or along single open joints.

Generally these major structures were near vertical, which created a problem when trying to intercept them with vertically drilled depressurization wells.  Either you hit one or you didn’t.

The use of directional drilling of pumping wells is a great innovation

Directional drilling of dewatering wells gives the opportunity to angle a pumping well to an orientation that allows the well bore to cut across vertical structures rather than paralleling them.   In addition, one could drill pumping wells near the pit crest targeting towards the ultimate pit bottom.  This may help improve drainage near the operating benches as the pit deepens and could eliminate the need to install inpit pumping wells if water becomes a problem.

Some open pits have constructed underground drainage galleries around the pit circumference to help intercept deep groundwater seepage.  Possibly directionally drilling aligned parallel to the pit wall can replace such high cost drainage galleries.

The bottom line is that the directional drilling innovation makes a lot of sense and mine operators should take a look at it.  It might help improve their pit dewatering systems.

If anyone has experience with directionally drilled dewatering wells, please let us know.

The hydrogeology at Diavik was unique in that the ground consisted of both permafrost and unfrozen ground.  It was likely that unfrozen ground would eventually form permafrost over time once exposed to the cold winter climate.  To read more about the hydrogeology at Diavik, check out this link “Hydrogeology At Diavik – Its Complicated“.

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