The only way to drill a high verticality borehole both in home and abroad is based on effective hole straightening, enhancing inclination surveying and on time straightening.

A new hinge type bottom hole assembly used in straight well for well inclining prevention and hole straightening was put forward account to the fact that the actual pendulum and packed drill assemblies were not satisfactory for inclining prevention and hole straightening in formations with strong natural deflecting build up capacity.

Based on the experience of freezing hole construction in Xuehu Coal Mine, this paper discussed the causes of hole slanting, anti-slanting measures and hole straightening methods.

This paper makes a calculation of bit side force to the flexible pendulum stem and pendulum stem on the basis of vertial and horizontal bending theory, which, theoretically, shows that flexible pendulum stem has a better inclination correction effect than pendulum stem.

To an inchined building with sand ushion beneath its foundation, the most economical and convinent way of inclination correction is usually scooping sand method.

A new well straightening control method for improving vertical precision of vertical drilling trajectory;