How, in fact, do they actually manage to change the direction that a drillhead is going? I sort of get how they tell where the drill head is located by remote telemetry, but…how do you make sure the drillhead is going to go where you want it to?
You put steel wedges around the casing before you insert the drill bit (following the addition of a new rod - the next 6-foot advance). This will deflect the drill bit off your present drilling line.
That’s for directional drilling. Left on its own, a drill almost always deflects, forming a spiral in the direction of the turn.
In the oilfield we called it whipstocking. - YouTube