Going Down-The-Hole

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Phil Norris

I said that I would get back to you on what has caught my eye on the process industry equipment front, so this time, I am having a look down-the-hole (or downhole as some know it).   This is an environment that has been described as the most violent and extreme on the Planet and this is an area that attracts a lot of media and governmental attention when things go wrong.

In my last editorial, I talked about one such instance of media attention, extracting petroleum gas from shale rock and the now infamous ‘fracking’ process.  What caught my eye was how extensively this process is used in exploration and exploitation of the Earth’s natural resources.

As a non-petrochem industry person, I know very little about the processes but after a little investigation, I now know that ‘fracking’ is used not only for gas extraction, but also for both creating underground reservoirs for water storage far underground  and, conversely, extracting fossil water.  If you search on Wikipedia for fracking, you can see what I mean.

As a serious Engineer, I have been amazed at some of the equipment that has been developed for use 3 miles down- the- hole where pressures can reach 1,700 bar (25,000psi) and 240°C.  Like Maxon Motor’s new EC 22 HD brushless DC motor that is used to control the drilling head.  Bathed in hot oil, having to withstand vibration of up to 25 grms and impact forces of up to 100G, these little motors, developing 240 watts, have to keep going for thousands of hours without attention – extreme or what!

Some of the downhole submersible pumps as found in deep water extraction applications,  have to be almost as tough.   Water utility companies use 4″ to 12″ diameter multi-stage centrifugal submersible pumps that have to be at once, constructed out of hygienic materials, have the highest electrical enclosure standards (IP67), operate in high pressure environments (up to 1,000 metre hydraulic pressure) and, of course, be robust and well designed to operate for years with little attention.

I marvel at the diagrams in the media and in technical papers that show how far from the vertical boreholes go thousands of feet down and miles away from the well head.  I got to wondering how they manage to get the drill head to precisely where the oil-bearing stratum is.    The easy to understand bit (sic) is establishing where the target area in Cartesian coordinates is; via seismic survey methods of course.

The more difficult part is to navigate the drilling head to that target area.  This has to be done by ‘dead’ reckoning day-to-day with perhaps an occasional seismic survey (carried out at great expense) to check where the drill is in relation to the target area.

The down-the-hole guidance controls at the drilling head include highly sophisticated accelerometers and tilt sensors (inclinometers) as part of the guidance equipment and these have to be tough to resist the extreme environment at the drill head.  Modern electronics make red reckoning an exact science.

Dead reckoning come a long way from when mariners of old used to measure the ship’s speed by throwing a log tied to a rope overboard and measured the number of knots on the rope that went through the matelot’s hands in a minute, the navigator calculated the course with the compass heading and average speed in knots and everybody hoped they all got within 26 miles of the target port.

Visit us again – Hasta la vista