Directional drilling - a simplified explanation.
Kerm,
Directional drillers have very sophisticated software that interprets the surveys given to it, and spits back very accurate numbers telling them where the bit is in 3-space.
Before I begin, my appologies to any directional drillers reading this (are you there Marc L. at Sperry-Sun?). This is not my area of expertise, but I've seen it done a thousand times - actually, more!!!)
It's done like this.
Surveys are generally taken at fairly short intervals, (every 10 feet, or every 10 metres, as the drilling program calls for.
The survey instrument is usually several metres back from the bit, and gives information about it's "true vertical depth" (distance from instrument to a point at the surface directly above it), it's "measured depth" (distance along the borehole's path), the angle it is resting at in the borehole (measured against a horizontal line), and it's "azimuth" (imagine it as the needle on a compass dial).
From this information, the software will tell the directional driller EXACTLY where the instrument is relative to the centre of the borehole at the surface, accurate to millimetres (sixteenth's of an inch, for you southerners!!!). It also gives an extrapolation for the position of the drill bit - don't forget it is several metres further along.
They always take surveys whilst drilling wells, directional or not, so an accurate trajectory in 3-space for the existing blown-out well should be easy to plot.
It is quite amazing really. It is very accurate and the principle is relatively simple.
Hope this helps, Kerm and everyone.
Rick. |
