ABSTRACT
When considering deviation in a drill hole it is probably more appropriate to accept the generality that there is no such thing as a straight drill hole. This chapter sets out with an element of mathematical precision the effects of bit weights, formation characteristics, drillcollar to hole clearance and stabiliser placement on deviation. The anisotropic formation theory was developed by researchers in the oil and gas industry wherein, given the extremes in hole depth, doglegs and deviation present a major problem. Arthur Lubinsky advanced the theory that deviation was the result of the drill pipe loaded in compression deflecting off the low side of the hole. Much of the basic theory established by oilfield researchers has a general area of application in other drilling activities but the size of the holes and rigs involved impose severe limitations on how far the practices can be followed.
