[Geezer (OP)]

It's hard enough to drill a straight hole in a piece of wood two inches thick, but how do these amazing drill rig operators (like the fantastic guys in Chile) manage to make a rock drill follow a curved path and hit a really small target thousands of feet underground?

[Bass]

They do it with mirrors []

[maffsolo]

Directional drilling Definition

"1. intentional deviation of a wellbore from the vertical. although wellbores are normally drilled vertically, it is sometimes necessary or advantageous to drill at an angle from the vertical. controlled directional drilling makes is possible to reach subsurface areas laterally remote from the point where the bit enters the earth. it often involves the use of turbodrills, dyna-drills, whipstocks, or other deflecting rods.

2. the intentional deviation of a wellbore from the path it would naturally take. this is accomplished through the use of whipstocks, bottomhole assembly (bha) configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors and special bha components and drill bits. the directional driller also exploits drilling parameters such as weight on bit and rotary speed to deflect the bit away from the axis of the existing wellbore. in some cases, such as drilling steeply dipping formations or unpredictable deviation in conventional drilling operations, directional-drilling techniques may be employed to ensure that the hole is drilled vertically. while many techniques can accomplish this, the general concept is simple: point the bit in the direction that one wants to drill. the most common way is through the use of a bend near the bit in a downhole steerable mud motor. the bend points the bit in a direction different from the axis of the wellbore when the entire drillstring is not rotating. by pumping mud through the mud motor, the bit turns while the drillstring does not rotate, allowing the bit to drill in the direction it points. when a particular wellbore direction is achieved, that direction may be maintained by rotating the entire drillstring (including the bent section) so that the bit does not drill in a single direction off the wellbore axis, but instead sweeps around and its net direction coincides with the existing wellbore. rotary steerable tools allow steering while rotating, usually with higher rates of penetration and ultimately smoother boreholes."

[chris]

What an excellent answer. Thank you. I learned a lot from that.

Chris

[JimBob]

Before the invention of all the complicated devices used in the two methids above, a good driller could do it by altering the combination of several variables he controlled from the surface.

These are:

weight of pressure put on the drill bit
speed of rotation of the drilling pipe
mud volume pumped through the drilling pipe
specific types of combinations for type of rock being drilled through
the way he held his cigar and the angle at which he spat 'baccy juice off the drill floor

There are certain to be things I have missed as the drillers always were rather tight lipped abut this. It was sort of a "Masonic Lodge" of drillers where the real keys to doing the job were kept from we mortal "company men."

[maffsolo]

Before the invention of all the complicated devices used in the two methids above, a good driller could do it by altering the combination of several variables he controlled from the surface.

These are:

weight of pressure put on the drill bit
speed of rotation of the drilling pipe
mud volume pumped through the drilling pipe
specific types of combinations for type of rock being drilled through
the way he held his cigar and the angle at which he spat 'baccy juice off the drill floor

There are certain to be things I have missed as the drillers always were rather tight lipped abut this. It was sort of a "Masonic Lodge" of drillers where the real keys to doing the job were kept from we mortal "company men."

Tough old birds, having years of experience!

I guess technology took the fun out of dentistry, doing miles long root canals in the blind.

How did they ever get by without GPS, wetting their thumb and hold it in the air?

[geo driver]

Feel, its a wonderful thing, somthing to admire, technology does take the charm out of thing. However, doing thing by feel leads to overconfidance, and catastrophic repercussions. I still like the thumb in the air though.